Ruprecht-Karls-Universität Heidelberg

Königstuhl Kolloquium


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2020-10-23
15:00
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The cycle of matter in the magnetized interstellar medium as revealed by machine vision
Juan Soler (MPIA)
Königstuhl Kolloquium
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Machine vision is the general name given to the methods for automatic inspection and analysis of images, from pattern recognition to object classification. I will present the results of machine vision techniques applied to the study of the formation and evolution of star-forming clouds in the Milky Way, both in observations and numerical simulations. First, the characterization of filamentary structures in the observations of the atomic hydrogen (HI) emission at 21 cm in The HI/OH/Recombination-line (THOR) survey of the Galactic plane. Second, the evaluation of the correlation between the HI emission and the emission from molecular species in star-forming clouds. Finally, in the study of the anisotropy introduced by the interstellar magnetic fields in the velocity field in and around star-forming clouds.

2020-10-30
15:00
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Anders Jidesjö & Svein Sjøberg (TBA)
Königstuhl Kolloquium
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Blocked for talk related to ROSE/IAU OAE.

2020-11-06
15:00
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TBD
Maryam Modjaz (NYU)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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2020-11-06
15:00
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Maryam Modjaz (NYU)
Königstuhl Kolloquium
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2020-11-13
15:00
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ASPECS - The ALMA Spectroscopic Survey in the Hubble Ultra Deep Field (www.aspecs.info)
Fabian Walter (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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I will report on some of the results emerging from the ALMA large program ASPECS (aspecs.info). ASPECS obtained deep imaging in the 1mm and 3mm bands of the Hubble Ultra-Deep Field (H-UDF) through frequency scans. The observations provide a full census of dust and molecular gas in the H-UDF, down to masses that are typical of main-sequence galaxies at redshifts 1-4. The resulting data products enable a great range of studies, from the characterisation of individual galaxies, capitalizing on the unique multi-wavelength dataset of the H-UDF, to CO excitation studies to constrain the gas properties of the distant galaxies. A 3D stacking analysis using precise redshifts from major VLT/MUSE initiatives on the field helped in recovering additional emission of galaxy samples that are too faint to be detected individually. Stacking in both the continuum and line (capitalizing on 100s of spectroscopic redshifts from major VLT/MUSE initiatives on the H-UDF) pushed the detection limits further. The nature of the observations (full spectral scans) provides a census of dust and molecular gas in the cosmic volume defined by the H-UDF. The resulting cosmic molecular gas density as a function of redshift shows an order of magnitude decrease from z=2 to z=0. This is markably different from independent measurements of the atomic gas phase that shows a rather flat redshift dependence. These measurements can be used to put new constraints on the gas accretion process that is needed to explain the build-up of stellar mass in galaxies through cosmic history.

2020-11-13
15:00
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Maryam Modjaz (NYU)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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2020-11-20
15:00
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Jonathan Henshaw (MPIA)
Königstuhl Kolloquium
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2020-11-27
15:00
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Patzer Colloquium (MPIA/ZAH)
Königstuhl Kolloquium
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2020-12-04
15:00
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HH2020 speaker (CfA)
Königstuhl Kolloquium
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2020-12-11
15:00
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Diederik Kruijssen (ARI)
Königstuhl Kolloquium
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2020-12-18
15:00
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Laura Kreidberg (MPIA)
Königstuhl Kolloquium
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2021-01-08
15:00
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Connecting the dots: Numerical models of AGN and their particle acceleration
F. Spanier (ITA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Active Galactic Nuclei are an interesting source not only for photons in a very wide energy range, but also for cosmic rays and neutrinos. The emission of these different messengers is most likely connected to each other. To understand the physics behind AGN, emission models have to be constructed. Nowadays observational data is available from radio frequencies to TeV energies and neutrino observatories like IceCUBE may provide ultra-high energy neutrino counts. Unfortunately long-term simultaneous multi-wavelength observations are still scarce. I will present results from time-dependent and spatially resolved AGN emission models that allow for a self-consistent treatment of emission and particle acceleration within AGN. These models may help to distinguish different emission processes using the timing of lightcurves in separate energy bands. But they may also provide answers to questions like "What is the shape of an AGN jet?" or "Is there really one neutrino per one high-energy photon?"

2021-01-15
15:00
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Brauer Award talk
Sarah Leslie (Leiden)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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2021-01-22
15:00
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Trifon Trifonov (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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2021-01-29
15:00
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Sarah Bosman (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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2021-02-12
15:00
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Dominika Wylezalek (ZAH/ARI)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Past events


2020-10-16
15:00
Constraining the Reionization History with the Most Distant Quasars
Fred Davies (MPIA)
Königstuhl Kolloquium
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The epoch of reionization was a pivotal moment in the history of the Universe when the cumulative output of ionizing UV photons from the first stars, galaxies, and accreting black holes surpassed the total number of hydrogen atoms in the intergalactic medium. Key uncertainties remain in the nature of both the sources and sinks of ionizing photons, but the time evolution of the intergalactic neutral hydrogen fraction provides a joint constraint on the formation of these early cosmic structures. I will summarize the crucial role that observations of the most distant, luminous quasars have played in constraining the neutral fraction during the epoch of reionization, both from a (recent) historical perspective and via new measurements of hydrogen Lyman-alpha damping wing absorption in newly-discovered quasars at redshifts above 7. I will also highlight several other promising avenues for constraining the reionization history, which will become even more powerful in the era of Euclid and JWST.

2020-10-09
15:00
Sgr A* - measuring the super massive black hole in the center of the Milky Way
Wolfgang Brandner (MPIA)
Königstuhl Kolloquium
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Invisible in the optical, a super massive black hole rules the center of the Milky Way. For its proof-of-existence and its study, Andrea Ghez (UCLA) and Reinhard Genzel (MPE) were awarded the Nobel prize in Physics 2020. I will briefly summarise the science highlights. MPIA contributed significantly to these discoveries with the near infrared camera CONICA, which was part of the adaptive optics system NACO at the ESO VLT, and the Coudé Infrared Adaptive Optics (CIAO) systems, which are part of the GRAVITY VLTI instrument. The main focus of the observations were the measurements of stellar orbits and the investigation of brightness outbursts in the immediate vicinity of the black hole, and a comparison with the predictions of Einstein's special and general theory of relativity.

2020-10-02
15:00
Zooming in on star and disk formation
Asmita Bhandare (MPIA/CRAL)
Königstuhl Kolloquium
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Magnetized, cold, dense molecular cloud cores provide the birth environment for stars and disks. The multi-scale scenario of low-mass star formation occurs via the formation of two quasi-hydrostatic cores. In this talk I will discuss results from numerical simulations used to probe the gravitational collapse process that involves the transition of an isolated molecular cloud core to a hydrostatic core with a surrounding disk. We use the PLUTO code to perform radiation (magneto-)hydrodynamic simulations using one- and two-dimensional (2D) grids. Additionally, we use for the gas equation of state density- and temperature-dependent thermodynamic quantities to account for dissociation, ionization, and molecular vibrations and rotations. Using spherically symmetric simulations we survey a wide range of initial low- to high-mass (0.5 - 100 Msun) molecular cloud cores, yielding the largest parameter scan so far. The results highlight that in the high-mass regime first hydrostatic cores do not have time to evolve because of the large accretion rates. We perform 2D collapse simulations with an unprecedented resolution to model the evolution of the second hydrostatic core. For the first time, these studies demonstrate the onset of convection within the second core for the collapse cases of non-rotating molecular cloud cores in the low-mass regime. This supports the interesting possibility that dynamo-driven magnetic fields may be generated during the very early phases of low-mass star formation. Furthermore, I will discuss the impact of different cloud properties on the formation of protostellar disks and the launching of magnetically driven outflows during the early stages of star formation. These models will serve as the foundation for follow-up studies that link theoretical insights with observational signatures.

2020-09-25
15:00
Probing dark matter models with dynamical and assembly histories of galaxies
Ryan Leaman (MPIA)
Königstuhl Kolloquium
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Small scale cold dark matter (CDM) problems have been reconciled with observations by considering the effect of stellar feedback on low mass galaxies. However viable alternative particle physics models for dark matter also alleviate these cusp-core and missing satellite problems. The next challenge in near-field cosmology is to develop techniques which separate the degenerate classes of solutions
(CDM+feedback vs. non-standard DM models) to small-scale structure problems in the Universe. I will discuss two complementary methods to address this: 1) composite gas and stellar kinematic observations of nearby galaxies to provide constraints on DM particle properties, and 2) a new method to recover galaxy accretion histories as a way to probe abundances of low mass subhalos. Together with existing direct detection experiments, these astrophysical tests provide an important way forward in studying a fundamental question in cosmology - what is dark matter?

2020-09-11
15:00
TBD
Arianna Musso Barcucci (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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2020-09-04
15:00
TBD
Sascha Quanz (ETH)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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TBD

2020-08-28
15:00
TBD
Asmita Bhandare (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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2020-08-07
15:00
Near-field cosmology with the rapid neutron-capture process
Alexander Ji (Carnegie)
Königstuhl Kolloquium
via zoom,
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In the first billion years of the universe, stars and galaxies formed in the smallest dark matter halos, produced high-energy photons that reionized the intergalactic medium, and polluted the universe with the first heavy elements. Near-field cosmology probes this early era by observing nearby relic galaxies that have survived from ancient times. In particular, the elemental abundances of their old, metal-poor stars encode otherwise inaccessible information about the first stellar populations and first galaxy formation histories. Decoding these abundances requires connecting nuclear and stellar astrophysics to galaxy formation and hierarchical assembly. I will show how stellar abundances of metal-poor stars have shaped our current understanding of the rapid neutron-capture process (r-process), including how they inform future multi-messenger observations of kilonovae. The r-process can in turn be used to build our understanding of the high-redshift universe, including galaxy formation in the faintest dwarf galaxies and the hierarchical assembly of our Milky Way's stellar halo.

2020-07-24
15:00
Witnessing the Assembly of Planetary Systems with ALMA
Richard Teague (CfA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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ALMA has undoubtedly revolutionized our understanding of the planet formation environment, the protoplanetary disk. Images of the stunning gaps, rings and spirals traced by the dust in these disks point towards a population of young planetary systems caught in the very early stages of their formation. In parallel to these advances in imaging the dust component, a second revolution has been underway looking at the gas component of these disks. With ALMA we are able to obtain spatially and spectrally resolved spectra of simple molecular species, achieving signal-to-noise ratios in the hundreds. Such high quality spectra have enabled detailed explorations of the kinematics of these planetary nurseries, revealing extremely dynamic environments containing flow structures associated with on-going planet formation. I will present a series of results examining the dynamical structure of protoplanetary disks, demonstrating how we can measure rotation curves at a meters-per-second precision and how these can be used to infer the 6D structure of the disk. Combining these techniques, I will further show how we can now detect embedded planets within these disk, enabling a novel view of planet formation and trace the delivery of atmosphere-building material to these embedded planets. To conclude, I will discuss how we can expand these techniques to transform ALMA into a sub-mm planet hunting instrument, probing a truly unique region of parameter space previously inaccessible with current instrumentation and providing essential context for contemporary exoplanet demographics.

2020-07-17
15:00
Understanding nuclear star clusters in low-mass galaxies through M54
Mayte Alfaro (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Nuclear star clusters (NSCs) are the densest stellar system known in the universe. They are hosted by a high fraction of galaxies at different mass ranges. The characteristics exhibited by NSCs in low-mass galaxies are similar to high-mass and chemical complex globular clusters (GCs). This suggests that some NSCs can be found as Galactic GCs, as remnants of dwarf galaxies accreted by the Milky Way. M54, the NSC of the Sagittarius dwarf spheroidal galaxy is a remarkable example of this type of objects. As it still lies at the center of its host at a distance where resolved studies are possible (27 kpc), M54 provides the unique opportunity to understand low-mass galaxy nuclei in their original environments. In this talk, I will present an unprecedented detailed study of M54. Using a large MUSE data set covering out to ?2.5 effective radii of M54, we extracted ?6600 member stars recovering the star formation history of this NSC. We detected at least three stellar subpopulations whose origin can be explained as the result of the combination of different NSC formation mechanisms.

2020-07-10
15:00
TBA
Rebecca Bowler (Oxford)
Königstuhl Kolloquium
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KoCo Signature Speaker

2020-07-10
15:00
Exploring the sources of cosmic reionization
: Maxime Trebitsch (MPIA)
Königstuhl Kolloquium
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Cosmic reionization is one of the last major milestones in the evolution of the Universe. It has only taken one billion years for the bulk of the hydrogen in the Universe to be fully ionized by the radiation produced by early galaxies and quasars. While significant progress has been made in the recent years, completing the census of these ionizing sources is still a major challenge on both the observational and theoretical sides.
In this talk, I will discuss how radiation hydrodynamical simulations can be used to study the properties of the first galaxies and AGN with a particular focus on their relative role in reionizing the Universe.

2020-07-03
15:00
Multiplicity properties of pre-supernova massive stars in the Magellanic Clouds
Lee Patrick (U. de Alicante)
Königstuhl Kolloquium
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Most massive stars reside in multiple systems with ?70% expected to interact during their lifetimes. These interactions have profound effects on the evolution of the stars in such systems and the nature of their subsequent supernova explosions, as well as on the formation of stellar mass black hole?black hole binaries. Red supergiant stars represent the final evolutionary stage of the majority of massive stars before supernova and remain the only confirmed progenitors to Type IIp SN. What is known about the multiplicity properties of this phase of evolution is either theoretical, extrapolated from earlier evolutionary phases or based on a very small sample of stars. I review the various evolutionary paths towards a RSG multiple system and present the latest observational and theoretical results on the multiplicity of RSGs, concentrating on the Large and Small Magellanic Clouds. We find a significantly smaller multiplicity fraction for RSGs than their evolutionary descendants. I discuss the implications of this important result and the limitations of the current observations where I stress the need for future high-precision and -accuracy spectroscopic studies of the Magellanic Clouds.



See More \;from Eva Schinnerer

2020-06-26
15:00
Zooming into the blast furnace - A close look into the molecular gas in the NGC253 starburst
Nico Krieger (MPIA)
Königstuhl Kolloquium
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n this talk I will present the results of my work as a PhD student over the past four years
at MPIA. In starbursts, such as the nearby galaxy NGC253, intense star formation creates


conditions that are believed to resemble those in high-z galaxies, and the strong
stellar feedback drives galaxy-scale outflows. We observed the molecular gas in
this extreme starburst environment in NGC253 at the unprecedented spatial

resolution of 2.5 pc with ALMA. Using this data, we study the molecular outflow
in detail, zoom into NGC253's central super star clusters and compare its
starburst to the similar but more quiescent center of the Milky Way.

2020-06-19
15:00
TBA
Sera Markoff (UVA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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KoCo Signature Speaker

2020-06-19
15:00
Uncovering the Onset of Planet Formation in Young Protostellar Disks
Sarah Sadavoy (Queens University/Canada)
Königstuhl Kolloquium
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Planets form in disks of dust and gas around young stars, where the growth of the dust grains are the first steps in the planet formation process. Constraining the onset of grain growth and the conditions under which it is favourable has been challenging in part because there has been a lack of observational tests that can be used to measure grain sizes in disks. Dust polarization from self-scattering processes offers a new opportunity to constrain grain growth in young disks, and thanks to the development of high resolution polarization capabilities, such observations are now possible. In this presentation, I will present an overview of the polarized self-scattering process and how it can be used to infer dust grain properties in disks. I will also highlight recent observational studies that have detected polarized self-scattering in young disks from ALMA and the VLA and the implications of these signatures for dust grain growth at early times (< 0.5 Myr). I will also discuss the challenges with using this mechanism and offer steps for what still needs to be done to utilize dust self-scattering to identify the building blocks for planets.

2020-06-12
15:00
atomic diffusion and mixing at the origin of chemical abundance variations.
Ekaterina Semenova (MPIA):We still do not understand physics of stars
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
The past decade revolutionised studies of Galactic structure and evolution. Large spectroscopic surveys, such as GALAH, APOGEE, RAVE, and LAMOST delivered spectra and chemical abundances for millions of stars in the Galaxy. \;However, this development also brought to light interesting peculiarities, which may have profound consequences for stellar astrophysics. \;It is common to assume that the surface abundances, determined by means of stellar spectroscopy, represent the composition of the ISM from which the star was born.  \;However, this assumption is controversial. Recent observational and theoretical studies suggest that individual chemical elements <\;<\;migrate>\;>\; inside the stars. The rate and direction of this migration depend on the chemical mixture, on the mass of a star and on its age, and, foremost, on the mass and atomic properties of the chemical element itself. This implies that the surface composition of a star is not equal to its birth composition. \;Given the physical diversity of transport processes, the question is: how can we constrain this migration? In this talk, I will give an overview of the problem from the observer's and modeller's perspective. I will furthermore, touch upon our recent findings, based on high-quality analysis of the Gaia-ESO survey data with 3D Non-LTE models. I will outline the physics behind the transport of elements in star, discuss the constraints that can be obtained from observations, and highlight broader consequences for studies of chemical enrichment of stellar populations in the Milky Way and in other galaxies

2020-06-05
15:00
Light Element Inhomogeneities and Multiple Populations in Globular Clusters
Jeffrey Gerber (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract

Globular clusters (GCs) are massive star clusters orbiting in the halo of the Galaxy and are some of the first objects to form in the Milky Way. Due to their old ages and large numbers of stars they are perfect objects to learn about the formation history of our Galaxy and the evolution of low mass stars. However, studies have shown that GCs are not simple homogeneous populations, but rather are home to multiple populations of stars with differing abundances in light elements such as C, N, O, and Na. In this colloquium, I will present research from my dissertation, which used a large data set to study these populations and the abundances of C and N in the evolved stars of these objects. We focus on three globular clusters, M53, M10, and M71. Our sample includes low resolution spectra of 100-150 stars in each cluster that span a large range of magnitudes, which allows us to study the effects of evolutionary processes on the surface abundances of C and N. We classify stars based on their N abundances into a N-normal and a N-enhanced population. Our results show that two populations of stars are found in all three clusters with both populations appearing in a similar ratio in all stages of evolution. We also find that stars in both populations experience the same rate of surface C depletion and N enhancement as they evolve. Finally, we compare our method of classifying stars to other methods present in the literature, and find no anomalous abundance patterns, and determine that all methods used on the three clusters studied agree on the number of populations in each cluster.

2020-05-29
15:00
Combining astrophysics and geology to study the formation of Earth and Venus
Seth Jacobson (Michigan State Uni)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
The accretion of Earth is a mysterious era in geologic history without any surviving rock record. However, this is when Earth's bulk geochemistry and geophysical structure was established. Using sophisticated astrophysical-geological modeling, we can reconstruct this era, date important events such as the Moon-forming event, and determine basic characteristics of the nascent protoplanetary disk. By considering the consequences for Earth, we can better understand the stark contrast of Venus--a planet without a planetary magnetic field, without plate tectonics, and without a Moon. This earliest eon which lies at the intersection of astrophysics and geology had profound consequences for life on Earth that are just beginning to be understood.

2020-05-22
15:00
Tracing Historic Mass Loss from Evolved Stars with Thermal Emission from Cold Dust
Thavisha Dharmawardena (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
Evolved stars play a key role in the life cycle of dust in the universe. Through strong winds and supernovae they inject the material reprocessed in their cores to the interstellar medium, replenishing the interstellar medium with heavy elements. As evolved stars are so numerous they are extremely effective in this role. In this talk I will explore the role of historic mass loss. The typical treatment of evolved stars only accounts for present day mass loss or assumes they undergo constant mass loss throughout their lifetime. Historic mass loss can be effectively traced using thermal emission from the dust which cools down as it moves away from the central star. We exploit Herschel/PACS and JCMT/SCUBA-2 observations to study this historic mass loss. These two sets of observations are especially powerful, tracing the radial variation in the circumstellar envelopes of evolved stars. We establish the presence of variations in mass loss for a sample of Milky Way evolved stars which can not be ignored when applied to galactic models. In addition to this, we explore variability at sub-mm wavelengths for a small sample of evolved stars, including Betelgeuse during its recent minimum, to understand the relationship between the sub-mm variability and the circumstellar envelope. Finally I will introduce an overview of my current work at MPIA which focuses on modelling the 3D distribution of dust in the Milky Way by exploiting data from large surveys including Gaia and SDSS.

2020-05-15
15:00
Supermassive black holes in cosmological simulations
Melanie Habouzit (MPIA)
Königstuhl Kolloquium
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Supermassive black holes of million solar mass and above are commonly hosted by massive galaxies, but are also present in local dwarf galaxies. Black holes are a fundamental component of galaxies and galaxy evolution, but their origin is still far from being understood. Large-scale cosmological simulations of 100 cMpc box side length are crucial to understand BH growth and their interplay with their host galaxies. In a new study, we compare the black hole population of six of these large-scale cosmological simulations (Illustris, TNG100, TNG300, Horizon-AGN, EAGLE, and SIMBA). For the first time, our homogenous analysis of these simulations allows us to explore how the simulation sub-grid models affect the build-up of the BH population and their correlations with galaxies properties. The next two decades will be dedicated to the exploration of the high-redshift Universe with upcoming space missions such as LynX, Athena, JWST, WFIRST. I will also present how we can use cosmological simulations with physical models for BH formation to prepare these missions and maximize their scientific return.

2020-05-08
15:00
Dynamical fingerprints in the exoplanets sample
Gabriele Pichieri (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
25 years of observations have produced a large sample of exoplanets, many hosted by the same star in multiplanetary systems, and their orbital periods are one of the most intriguing distributions. An interesting and puzzling feature is the dearth of mean motion resonances, which are instead a predicted outcome of formation scenarios for the very common Super-Earth-type planets: although we do observe some resonant chains, most systems are not in resonance. In this presentation I will describe the main aspects of mean motion resonances, which also allows to understand why they are a preferred outcome for Super-Earths in the protoplanetary disc phase. Then, I will discuss how planetary instabilities in the Gyr evolution after the disc phase can reconcile this scenario with the observed exoplanetary architecture. Thus, I will present a novel dynamical mechanism which can be responsible for breaking the resonant chains. Finally, two other features of the period ratio distribution will be discussed: the population of multi-systems with period ratios wide of exact resonant commensurability, and the role of closely-packed systems.

2020-04-24
15:00
From exoplanet atmospheres to planet formation
Paul Moliere (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract


If one wants to know more about exoplanets than their most basic properties (such as mass and radius), turning to spectroscopy is essential. Spectra probe the planetary atmospheres and encode their composition, temperature structure and dynamics. Such observations are therefore crucial for understanding the atmospheric state of exoplanets. In addition, they may help us to unlock how planets form, namely by linking atmospheric composition to the planets' accretion of different building blocks from the circumstellar disk. In this talk I will give a summary on the techniques and challenges of atmospheric characterization. I will then present my own work towards the understanding of exoplanet atmospheres, and how this may be used for constraining planet formation in the future.


2020-04-17
15:00
From supernova rates and delays to progenitors and nucleosynthesis history
Dan Maoz (Tel-Aviv U.)
Königstuhl Kolloquium
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Abstract
Supernovae are Nature's almost-exclusive way of producing the elements from oxygen to iron. Roughly half of the world's iron was formed in so-called Type Ia supernovae (SNe Ia), the thermonuclear explosions of some white dwarf stars. SNe Ia have gained fame as distance indicators that first revealed the dark-energy-driven accelerating universal expansion. However, the precise identity of the exploding systems in SNe Ia, and their explosion mechanism, are major unsolved puzzles. Valuable clues are provided by the delay-time distribution (DTD): the spread of times between the formation of a stellar population and the explosion of some of its members as SNe Ia. I will show how recent attempts to measure the DTD, combined with other evidence, suggests that SNe Ia result from double white-dwarf systems that lose orbital energy to gravitational waves, merge, and explode. In parallel, I will show ongoing work to take the census of the Milky Way's double-white-dwarf systems, before they merge. The observed DTD permits attempting a reconstruction of the history of element creation in our Galaxy and in the Universe as a whole.

2020-04-03
15:00
The importance of environment for protoplanetary discs
Andrew Winter (ARI)
Königstuhl Kolloquium
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Abstract

Although most models aiming to synthesise the observed exoplanet architectures consider a protoplanetary disc evolving in isolation, this does not reflect the physical reality for many discs. Since stars form in regions of enhanced stellar density, feedback mechanisms play an important role. In particular, UV fields heat the disc and drive a photoevaporative wind, depleting the disc and decreasing the dispersal time-scale. I review the demographics of local star forming regions, and compare them to those regions that are the focus of observational studies of protoplanetary discs, demonstrating that well-studied discs are not typical. I present the evidence for the depletion of discs in various regions by external photoevaporation. Finally, I discuss how, as well as being an important consideration in understanding exoplanet populations, external photoevaporation can be used as a probe of both star formation and disc physics.

2020-03-27
15:00
TBD
Jonathan Henshaw (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
TBD

2020-03-27
15:00
We still do not understand physics of stars: atomic diffusion and mixing at the origin of chemical abundance variations
Ekaterina Semenova (MPIA)
Königstuhl Kolloquium
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Abstract

The past decade revolutionised studies of Galactic structure and evolution. Large spectroscopic surveys, such as GALAH, APOGEE, RAVE, and LAMOST delivered spectra and chemical abundances for millions of stars in the Galaxy. \;
However, this development also brought to light interesting peculiarities, which may have profound consequences for stellar astrophysics. \;

It is common to assume that the surface abundances, determined by means of stellar spectroscopy, represent the composition of the ISM from which the star was born.  \;However, this assumption is controversial. Recent observational and theoretical studies suggest that individual chemical elements <\;<\;migrate>\;>\; inside the stars. The rate and direction of this migration depend on the chemical mixture, on the mass of a star and on its age, and, foremost, on the mass and atomic properties of the chemical element itself. This implies that the surface composition of a star is not equal to its birth composition. \;
Given the physical diversity of transport processes, the question is: how can we constrain this migration?

In this talk, I will give an overview of the problem from the observer's and modeller's perspective. I will furthermore, touch upon our recent findings, based on high-quality analysis of the Gaia-ESO survey data with 3D Non-LTE models. I will outline the physics behind the transport of elements in star, discuss the constraints that can be obtained from observations, and highlight broader consequences for studies of chemical enrichment of stellar populations in the Milky Way and in other galaxies.

2020-03-27
15:00
Understanding the gas dynamics in the central 3 kpc of the Milky Way
Mattia Sormani (ZAH/ITA)
Königstuhl Kolloquium
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Abstract
I will give an introduction to the gas dynamics in the central region (R<3kpc) of the Milky Way, which is characterised by strong non-circular motions driven by the non-axisymmetric gravitational potential of the Galactic bar. After reviewing the basic theoretical tools, I will discuss how these can be used to interpret observations, and in particular the longitude-velocity maps of CO, HI and other tracers in the region | | | < 30 degrees. I will then discuss several applications, for example how this can be used to constrain the properties of the bar, and to estimate the accretion rate onto the Central Molecular Zone (the star-forming nuclear ring at R~150pc). Finally, I will highlight some open questions and directions of future research.

2020-03-27
15:00
Understanding the gas dynamics in the central 3 kpc of the Milky Way
Mattia Sormani (ZAH/ITA)
Königstuhl Kolloquium
Via zoom link. Please contact organisers if you need the zoom information.,
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Abstract
I will give an introduction to the gas dynamics in the central region (R<3kpc) of the Milky Way, which is characterised by strong non-circular motions driven by the non-axisymmetric gravitational potential of the Galactic bar. After reviewing the basic theoretical tools, I will discuss how these can be used to interpret observations, and in particular the longitude-velocity maps of CO, HI and other tracers in the region | | | < 30 degrees. I will then discuss several applications, for example how this can be used to constrain the properties of the bar, and to estimate the accretion rate onto the Central Molecular Zone (the star-forming nuclear ring at R~150pc). Finally, I will highlight some open questions and directions of future research.

2020-03-20
15:00
The mass budget of planet-forming disks
Anna Miotello (ESO)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract



Protoplanetary disks are thought to harbor the sites of on-going planet formation. Therefore, it is important to understand the spatial distribution, the physical and chemical properties of protoplanetary building blocks to understand planet formation mechanisms and their planetary system demographics. In this context, the total disk mass and the disk surface density distribution are probably the most fundamental properties. Determining the total disk mass \;? \;which is dominated by the gaseous component \;? \;has proven to be very challenging. On one hand dust-based disk masses depend on the assumptions on the dust properties, on the optical depth of the continuum emission and on the gas/dust ratio, and on the other hand molecular hydrogen is invisible at mm wavelengths. Large surveys of disks carried out with ALMA in different star forming regions have targeted CO isotopologues as gas mass tracers. A result that is common to these surveys is that CO emission from disks is fainter than expected. As a consequence, the overall CO-based gas-masses are very low, and global gas/dust mass ratios are much lower than the expected interstellar-medium value of 100. This may be interpreted as lack of gas due to fast disk dispersal, or as lack of volatile carbon that leads to faint CO lines. After summarizing the results from different ALMA disk surveys and their implications, I will present alternative observational strategies which may help us to disentangle between the gas dispersal scenario and the chemical evolution hypothesis, for example using HD and hydrocarbon observations. Finally, I will present how current and future observations could be used to constrain the disk surface density distribution.

2020-03-20
15:00
The colourful past and dark side of galaxies unveiled through population-dynamics of their stars
Glenn van de Ven (U. Vienna)
Königstuhl Kolloquium
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Abstract

Driven by gravity, galaxies continuously grow through accretion of smaller systems. Stellar streams are nice illustrations of this hierarchical build-up, but the accreted stars quickly disperse. I will present advanced dynamical models that can convert the observed positions and velocities of the accreted stars to phase-space quantities like energy and angular momentum which remain conserved. In addition, these models can include the observed chemical properties of stars which are also conserved. The resulting population-dynamical models allow us then to uncover even those accretion events which are now fully dispersed. At the same time, these models also accurately constrain the total mass distribution, including a central black hole and dark matter halo.



I will illustrate how these models make optimally use of observations to unveil the dark side and colour past of galaxies: from accurate measurements of their dark halo, to unveiling the formation history of their disk and spheroid components, to uncovering the satellite accretion history. By the end, I aim to have demonstrated that these models provide a unique bridge between the studies of resolved stars in the Milky Way and integrated-light of high-redshifts galaxies. Together with direct coupling to state-of-the-art galaxy formation simulations, these population-dynamical models enable us to uncover the hierarchical build-up of galaxies in a cosmological context.

2020-03-13
15:00
On the radial structure and gas release of exoKuiper belts
Sebastian Marino (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
Planetary systems are not only composed of planets but also of belts of minor bodies with sizes ranging from ?m to km, analogous to the asteroid and Kuiper belts. This non-planetary component provides unique information on the formation, architecture, dynamics and evolution of planetary systems, as well as playing an important role in the delivery of volatiles to Earth-like planets. Collisions within these belts grind down solids resulting in high dust levels that are readily detectable around 30% of stars. In this colloquium, I will summarise the state of the art in the study of "exoKuiper" belts and show how my research at MPIA fits in this subfield of planetary research. I will show how ALMA has revolutionised the field by providing images at an unprecedented resolution of this type of circumstellar dust which traces the distribution of their parent km-sized planetesimals. Using ALMA I have characterised the radial structure in these belts, finding annular gaps that hint at the presence of Neptune analogues clearing their orbits at tens of au. ALMA has been also the first instrument capable of detecting and imaging circumstellar gas in these mature systems. This gas is of secondary origin and released by volatile-rich planetesimals (exocomets) in the same collisions that produce the observed dust. At MPIA, I have developed the first population synthesis model to study the evolution of this gas to constrain the timescales at which it viscously evolves and how it could affect the atmospheres of planets on orbits closer to the star.

2020-03-06
15:00
Mapping Milky Way Dust in 3D using Stars
Greg Green (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
Many precision measurements in astronomy depend on a careful treatment of dust reddening. Historically, two-dimensional maps of dust based on far-infrared thermal emission, such as the SFD and Planck maps, have found extensive use. However, an alternative method for measuring dust extinction relies on stellar photometry. Unlike far-infrared dust emission, stars can be used to trace the distribution of dust along the distance axis, as well as variations in the wavelength-dependence of extinction. Dust maps based on stellar photometry have additional desirable properties, such as the fact that their errors should be uncorrelated with large-scale structure.
I will discuss a 3D map of dust in the Northern Hemisphere, based on photometry from Pan-STARRS 1 and 2MASS, as well as astrometry from Gaia. I will also discuss ongoing work to extend this map to the South using the recently completed DECaPS survey, which was conducted with the Dark Energy Camera on the 4m Blanco telescope at CTIO. This work relies on accurate models of stellar photometry. In closing, I will therefore discuss my work to improve these models and understand variation in the dust extinction spectrum by applying machine learning methods to a combination of stellar spectroscopy, photometry and astrometry.

2020-02-28
15:00
Orion and the solar neighbourhood
Eleonora Zari (MPIA):Surveying young stars with Gaia
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
OB associations are loose groups of young, massive stars. They constitute the last stage of the massive star
formation process, and the context in which new stars are formed. Although OB associations have long been studied, it is not clear how they form and disperse in the field and what are the characteristics of their stellar populations.
The data of the Gaia satellite are crucial to unravel the structure and star formation history of the young associations, as they allow to study their spatial structure, kinematics, and ages with unprecedented precision.
In this talk, I will discuss the properties of the stellar groups in the Orion OB association, and
I will describe the three dimensional arrangement of young stars in the solar neighbourhood,
providing a view of the spatial configuration of young star forming regions within 500 pc from the Sun.

2020-02-21
15:00
The Origin of Stellar Masses
Mark Krumholz (ANU)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
The mass distribution of newborn stars, known as the initial mass function (IMF), has a distinct peak at a mass slightly less than that of the Sun. This characteristic stellar mass appears to be nearly invariant across a huge range of star-forming environments within and beyond our Galaxy, and seems to have changed little over most of cosmic time. Explaining its origin and universality is one of the oldest problems in theoretical astrophysics, but a fully successful theory eludes us even today. In this talk, I review theoretical attempts to explain the characteristic mass of stars, and discuss recent progress suggesting that we may be within reach of a solution.

2020-02-14
15:00
Mapping the hot Universe: eROSITA on SRG and its followup programs with SDSS-V and 4MOST
Andrea Merloni (MPE)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
The emergence of the three-dimensional structure of the cosmic web over the history of the Universe displays very distinctive features when observed in X-rays, where both the most massive collapsed structure (clusters of galaxies) and the most energetic events in the life of galaxies (AGN and Quasars) reveal themselves unambiguously.

The next generation of wide-area, sensitive X-ray surveys designed to map the hot Universe will be heralded by eROSITA (extended ROentgen Survey with an Imaging Telescope Array), the core instrument on the Russian-German Spektrum-Roentgen-Gamma (SRG) mission, successfully launched in July 2019. On December 8, after completion of its Calibration and Performance Verification phase, SRG/eROSITA has begun its four-years program dedicated to surveying the entire sky eight times in the energy range ~0.2-7 keV.

The high sensitivity, large field of view, high spatial resolution and high survey efficiency of eROSI

2020-02-07
15:00
Stars, Gas, and Dust in the Triangulum Galaxy
Thomas Williams (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
The Triangulum Galaxy (M33), is the third nearest spiral galaxy to us (behind the Milky Way and Andromeda), but is an interesting contrast to those galaxies. With a half-solar metallicity, and a much higher star-formation efficiency, the properties of M33 seem to be significantly different to the other 2 massive spirals in our Local Group, and may offer us more of a look at a ?younger', or higher redshift galaxy. I'll be talking about the 3 projects that made up my thesis, studying the interplay between the dust, gas, and stars in M33.

Firstly, I will present a study of the resolved star-formation law (or Kennicutt-Schmidt law) ? how this varies with the resolution it is measured at, and the gas tracer that is used. Secondly, using new SCUBA-2 PI observations of M33, I have created a dust-selected GMC catalogue, studying the gas-to-dust ratios (GDRs) and CO conversion factors in these clouds, as well as hunting for molecular hydrogen that CO may miss. Finally, using the data I have brought together over the course of my PhD, I have built a radiative transfer model of M33. This has been to study the sources of dust heating, and the scale at which a local dust-energy balance (i.e. the area at which the emission from dust is from starlight in that same area) is an acceptable assumption.

2020-01-31
15:00
The Demographics of Protoplanetary Disks: from Lupus to Orion
Sierk van Terwisga (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
In recent years, ALMA has opened up unprecedentedly detailed views of
the properties of planetary disks, and on their links to planetary
systems: the deep, high-resolution images of TW Hya, HL Tau and the
DSHARP survey are famous examples. But what does a 'typical'
protoplanetary disk look like -- and how do its properties change over
time, and in different environments?
ALMA's unique combination of speed and sensitivity enables us to survey
large samples of disks relatively quickly, and describe some of the key
parameters of protoplanetary disks from a population-level view.
In this colloquium, I will discuss surveys of protoplanetary disks in
Lupus, Orion A, and Orion B, focusing on the radii and masses of disks.
By comparing these regions' disks to each other, and to other surveyed
populations, we can begin to disentangle the competing impacts of
environment and age on the evolution of circumstellar material.

2020-01-24
15:00
The outcome of massive star formation
Maria Ramirez-Tannus (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
Massive stars play a crucial role in the Universe. They shape their surroundings by injecting large amounts of energy and momentum and they produce new, heavy elements that are the building blocks of new stars, planets, and life. They are usually observed in close binaries. Due to the lack of observations covering the earliest stages of their lives, the formation process of massive (binary) stars is poorly understood. I will present observational studies of the outcome of massive star formation. I will show the first spectroscopically confirmed population of massive pre-main sequence stars in the giant HII region M17 where we measured their temperature, luminosity, radius, and projected radial velocity. I will discuss their multiplicity properties and show that the young stars in M17 have a very low radial velocity dispersion in comparison to somewhat older stellar clusters of similar mass. I will present evidence for the hypothesis that massive stars are formed in binaries with wide orbits that shrink in the first few million years of evolution. Finally, I will present ongoing projects to test the wide binary hypothesis.

2020-01-17
15:00
Merger-triggered Star Formation: Where and How?
Hsi-An Pan (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
Galaxy interactions are often accompanied by an enhanced global star formation rate (SFR). The enhanced global SFR has been attributed to the formation of non-axisymmetric structures that torque significant amounts of gas into the central regions, initiating an intense nuclear starburst. Yet there is mounting evidence for extended starburst in interacting galaxies.

The talk will show an empirical picture of the spatial extent of merger-triggered star formation as a function merger sequence using data from the integral field spectroscopy (IFS) survey MaNGA. In addition, we also investigate the molecular gas properties to better understand what causes the enhanced star formation in galaxy mergers. This is the first time that the spatial extent of merger-triggered star formation and the dependence of molecular gas properties on merger sequence/configurations are probed statistically with a relatively large sample and with a carefully-selected control sample for individual galaxies.

2019-12-06
15:00
Characterizing the formation mechanisms of protostellar disks: observations and models
Anaelle Maury (CEA/Saclay)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
Understanding the first steps in the formation of stars and protoplanetary disks is a great unsolved problem of modern astrophysics. Observationally, the key to constraining theoretical models lies in high-resolution studies of the youngest protostars. \;
I will present the state of the art regarding observations and modeling of the youngest protostellar disks, observed less than 0.1 Myrs after the onset of protostellar formation. \;
In a first part, I will show how our millimeter dust continuum interferometric data suggests that most (>\;75%) protostellar disks observed less than 0.1 Myrs after the onset of protostellar formation are only found at very small radii <\;60 au, which favors magnetized models for protostellar disk formation. I will also present our ALMA observations of a very young solar-type protostar suggesting a disk is currently forming in counter-rotation with respect to the protostellar core rotation, and discuss potential scenarii to understand this oddity. I will show our SMA and ALMA observations of the magnetic field topology in a sample of young protostars and compare all observed protostellar properties to the typical outcome of models for protostellar formation. I will argue that our observations of small disks, counter-rotating disks and organized magnetic fields in the youngest star-forming cores question the established paradigm of disk formation as a simple consequence of angular momentum conservation during the main accretion phase: they instead highlight the need to investigate magnetized models in order to unveil the mechanisms responsible for protostellar disk properties.
In a second part, I will show both our observations and models of the dust continuum emission call for significant grain growth (grains larger than 10 microns and up to submillimeter sizes) at radii 100-1000 au in the protostellar envelopes observed less than tenth of a million years after the onset of collapse. I will describe new avenues to explore dust pristine properties and describe better in the future, for example, the initial conditions for the formation of planetesimals.

2019-11-29
15:00
D. Liu, M. Rugel & I. Smirnova-Pinchukova
Patzer Colloquium (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
D. Liu, M. Rugel & I. Smirnova-Pinchukova will give each a 20min presentation of the Patzer-award paper. Afterwards, we will have a reception to celebrate the winners.

2019-11-22
15:00
Tracing early nucleosynthesis in-/directly in the Universe
Camilla Hansen (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
Understanding how the heavy elements are produced in the early Universe remains one of the open questions in astrophysics. We seek to trace the first chemical enrichment from the First Stars (Pop III stars), which are long gone, and which we due to observational limitations cannot observe directly. Hence, we are forced to explore the properties and physics of this first population of stars through indirect measurements of the second generation stars. Bona fide second generation stars preserve to a great extent the gases and thus the traces of the Pop III stars in their surfaces. As we observe the old metal-poor stars in greater numbers we see that these are typically C-rich and often contain varying amounts of heavy elements. The amount of heavy element content is a direct tell about the Carbon Enhanced Metal-Poor (CEMP) stars nature and origin. It therefore becomes of utmost importance to understand the source of the heavy element production. Until the recent years, the heavy element nucleosynthesis could only be explored indirectly, however, thanks to a-LIGO's gravitational wave detections and the following ground-based observations of the electromagnetic wave signal, we can for the first time directly study the formation of radioactive heavy element nucleosynthesis taking place in the rapid neutron-capture process hosted by a kilonova. I will describe the manifold nature of CEMP stars, their origin, and link this to the r-process.

2019-11-15
15:00
New Light on Standard Candles: Putting Hubble Constant Measurements to the Test using High-precision Observations of classical Cepheids
Richard Anderson (ESO Garching)
Königstuhl Kolloquium
MPIA lecture hall,
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Abstract
Recent research has established a remarkable discord among determinations of Hubble's constant, H0, that measures the local expansion rate of the Universe. The value of H0 measured using an empirical distance ladder is 9% larger than the value inferred from precise observations of the oldest observable radiation, the Cosmic Microwave Background, using a cosmological model. The 4.2 sigma significance of these discordant H0 values is at least remarkable\; at most, it could indicate a need to modify cosmology, placing us a the brink of a possible breakthrough in physics. However, systematic uncertainties involved in H0 measurements require more detailed inspection before new physics can be credibly invoked.

Here I present research aimed at improving the astrophysical basis of the empirical distance ladder and mitigating systematic uncertainties related to classical Cepheids. First, I present the Geneva Cepheid Radial Velocity Survey (GE-CeRVS), which is used to support accurate parallax measurements and has uncovered previously unknown spectral variability phenomena that lead to systematic errors of Baade-Wesselink type distances. Next, I briefly describe the effects of rotation on the evolution of Cepheids and why rotation is relevant for testing evolutionary models and inferring Galactic structure. In the final part, I discuss distance scale biases arising from differences between local and distant Cepheid populations that are becoming increasingly important as the distance ladder is being extended to include ever more distant supernova host galaxies.

2019-11-08
15:00
Dense gas and star formation in nearby starburst galaxies with ALMA
Christine Wilson (McMasters)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
With its high sensitivity, excellent angular resolution, and wide spectral coverage, ALMA is revolutionizing our view of galaxies in the nearby universe. ALMA is particularly important for studying the dense molecular gas that is the fuel for star formation. Radio continuum emission from ALMA is also an important measure of the star formation rate, particularly in galaxies with high visual extinction such as starburst galaxies and luminous infrared galaxies. Finally, the ALMA archive contains an ever-growing collection of data that can be mined and combined to produce large samples of targets that can match or exceed the amount of observing invested in a single ALMA large program. I will describe our work on the link between dense gas and star formation for a sample of 9 nearby galaxies from the ALMA archive, which includes measuring the resolved Kennicutt-Schmidt star formation law at extreme star formation rate surface densities and identifying a new molecular line that appears to be an excellent tracer of the densest star forming gas.

2019-10-25
15:00
Revealing the mysteries of gas giant planets
Ravit Helled (Zurich)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
Planets are common and mysterious astrophysical objects. Giant planets are key planets to investigate because they have a critical role in shaping the architecture of young planetary systems and their composition provides information on the physical and chemical properties of proto-planetary disks, the birth places of planets.
Gas giants are thought to have heavy-element cores in their deep interiors, and the division into a core and hydrogen-helium envelope is applied in both formation and internal structure models.
However, recent giant planet formation and evolution simulations show that this is an over-simplification. First, I will present updated formation and evolution models that follow the heavy-element distribution imply that giant planets are inhomogeneous and are expected to have dilute/fuzzy cores. I will then present updated structure models of Jupiter that fit the recent measurements of the Juno mission and discuss the importance of these results for our understanding of Jupiter's origin, and for the characterization of giant exoplanets.

Signature Speaker

2019-10-18
15:00
Accretion and Feedback in High-Mass Star Formation
Rolf Kuiper (Uni Tuebingen/MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
In the course of their accretion phase, massive (proto)stars impact their natal environment in a variety of feedback effects such as thermal heating, MHD-driven protostellar jets and outflows, radiation forces, and photoionization / HII regions. Here, I present our most recent simulation results in terms of the relative strength of the feedback components and the size of the reservoir from which the forming stars gain their masses. For the first time, these simulations include all of the feedback effects mentioned above which allows us to shed light on the physical reason for the upper mass limit of present-day stars. Furthermore, we predict the fragmentation of massive circumstellar accretion disks as a viable road to the formation of spectroscopic massive binaries and the recently observed strong accretion bursts in high-mass star forming regions.

To advertise our latest code development, I will also overview the most recent results obtained in a variety of other astrophysical research fields from the formation of embedded Super-Earth planets' first atmospheres (Cimerman et al. 2017, MNRAS) to the formation of the progenitors of the first supermassive black holes in the early universe (Hirano et al. 2017, Science).

2019-10-11
15:00
Towards more robust and explainable neural nets: Beyond the black box
D. Finkbeiner (CfA)
Königstuhl Kolloquium
MPIA lecture hall,
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Abstract
Deep neural nets have achieved ever greater successes in recent years, but there is still a pervasive sentiment in our field that "they are black boxes" and "we will never understand them." A thorough understanding remains elusive, but we can conceptualize what a neural net is doing using familiar tools and concepts, such as probability distribution functions, fitting functions, and Bayesian statistics. We can leverage results from the field of "Adversarial AI" to study important failure modes, and learn how to mitigate them by addressing the underlying cause of failure. By training neural networks better, using them better, and evaluating their performance better, we may be able to apply these powerful tools to astronomical problems with sufficient rigor to make them broadly palatable.

2019-09-27
15:00
First Steps of Planet Formation: Models & Observations
Paola Pinilla (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
In this new era of powerful telescopes such as ALMA, we are now able to study the birth of planets in disks around young stars, in more detail than ever before. New observations are revealing fascinating structures in protoplanetary disks that are transforming our understanding of the formation and evolution of planetary systems. In this colloquium, I will explain theoretical models of dust evolution in protoplanetary disks and I will compare these theoretical predictions with current multi-wavelength disk observations. This link is providing significant insights about how different physical conditions play a crucial role in the formation of the first planetesimals, and is extending our understanding of how initial conditions of protoplanetary disks are reflected in the large diversity of extrasolar systems observed up today.

2019-09-13
15:00
The rise and fall of cosmic star formation
Sarah Leslie (MPIA)
Königstuhl Kolloquium
MPIA lecture hall,
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Abstract
Galaxies grow on timescales of millions of years, so it is not an easy task to observe their changes directly. Instead, we collect observations for thousands of galaxies of different ages to infer how galaxy populations evolve over time. Dust is a small but important component of galaxies, obscuring on average 1/3 of the stellar light in local galaxies. I will discuss how this obscuration changes as a function of redshift using samples from the Sloan Digital Sky Survey (SDSS) and the Cosmic Evolution (COSMOS) survey. I will then present a promising way to circumvent uncertainties from dust attenuation by using observations at radio wavelengths. With dust-unbiased 3GHz observations of the COSMOS field, I have derived average star formation rates of galaxies from redshift 0.2 to 5, following the rise and fall of star formation activity in the Universe. I show the fraction of star formation activity occurring in galaxies of different stellar masses, morphological types, and environment. I find evidence that more massive galaxies live fast and die young, with the growth of bulges being an important aspect of this evolution.

2019-09-06
15:00
Modeling embedded star formation
Michael Kueffmeier (ITA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
Stars are embedded in di?erent environments of Giant Molecular Clouds during their formation phase. Despite this fact, it is common practice to assume an isolated spherical core as the initial condition for models of individual star formation. To avoid the uncertainties of initial and boundary conditions, we use an alternative approach of zoom-in simulations to account for the environment in which protostars form. Our magnetohydrodynamical simulations show that the diversity in protostellar environments is reflected in the accretion process of protostars, as well as in the disk formation process. Regarding protostellar multiples our analysis suggests that companions initially form with wider separations of ~1000 au and afterwards migrate to smaller separations of ~100 au from the primary star. Against the background of observations of bridge-like structures such as seen for e.g. IRAS 16293-2422, we find that similar structures emerge as transient phenomena during protostellar multiple formation. To account for infall events of single stars at later times, we study how encounter events with gas condensations affects the properties of the star and the properties of its disk.

2019-08-30
15:00
Double stars are trouble stars: Close pairs in Gaia DR2, DR3, DR4
Uli Bastian (ZAH/ARI)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
On the one hand, double stars are a nuisance for data reductions. On the other hand, they are scientifically interesting and important. After all, binaries probably constitute the majority of the overall stellar population. Thus they are crucial e.g. for our understanding of the formation of stars and planets in general. The Gaia mission sees, discovers, measures and parameterizes double stars - both optical pairs and physical binaries - in a surprising multitude of ways. Each of these ways poses an operational challenge as well as a scientific chance. Once fully exploited they will give a strongly revised picture of stellar binarity statistics. And they will remove all the disturbances caused by duplicity in the astrometric and photometric data of Gaia DR2. Gaia DR1 achieved an effective angular resolution (i.e.pair separations) of 2 arcsec, DR2 of 0.4 arcsec. But the actual optical resolution of the Gaia instrument is about 0.15 arcsec, and there are ways to detect and measure pairs down to the milli-arcsec level. All this can be done for hundreds of millions of stars, but it means a few more years of hard work by the Gaia data reduction consortium.

2019-08-02
15:00
The Industrial Revolution of Galactic archaeology
Sven Buder (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
How did the Milky Way form and evolve? Which processes shaped its structure at which times?
Stars as Galactic time capsules are our best tracers to answer these questions and in the recent years we have made revolutionary progress in observing their properties in large samples.
We have come to realise that our traditional picture of the Milky Way as a composite of three main stellar components (halo, disk, and bulge) is too simplistic - the stellar properties overlap and reveal great complexity. In order to confirm or reject formation scenarios of the Milky Way, we have to understand how the stellar properties come about and are interlinked.
I will outline the challenges that come with the collection of big data from stellar spectroscopic surveys, such as the 'Galactic Archaeology with HERMES' (GALAH) survey, and show which efficient and automated techniques we have developed to manage the very large data flow of stellar surveys.
In the course of my PhD, I have used the chemical information from GALAH together with dynamical information and stellar ages to analyse the Galactic disk in the solar neighborhood in order to disentangle the complex nature of the two populations of the disk. One of the big open questions is which role did accretion play in the formation of the disk populations? Could the recently (re-)discovered accreted halo stars of Gaia-Sausage/Gaia-Enceladus have caused the drastic change in the evolution of the disk?
During the KoCo I will guide you through the last 4 years of my journey in exploring the Milky Way and its chemodynamic information with the aim to shed light on the above mentioned questions.

2019-07-26
15:00
How (not) to select targets for a spectroscopic survey
David Hogg (NYU, MPIA)
Königstuhl Kolloquium
HdA auditorium,
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Abstract
The scientific capabilities of a spectroscopic survey depend on the spectroscopic data quality, on how the targets were selected, and on how well that selection can be quantitatively characterized. For many projects, the target selection and its characterization are the biggest sources of uncertainty for important results. There are many large spectroscopic programs in operation and starting in astrophysics. These range from cosmological large-scale structure mapping experiments, to large Galactic archaeology and stellar physics projects, to extreme-precision radial-velocity surveys for exoplanets, to follow-up of real-time events in streams from time-domain imaging surveys. In all of these cases, there will be important long-term scientific goals for these spectroscopic programs that depend on being able to make statistical inferences. For example, what is the distribution in phase space of stars with particular element abundances and ages? Or what is the occurrence rate of exoplanets of certain types at certain periods? In order for these questions to be answerable in the end, projects must be able to produce (at least approximate) selection functions. That requirement, in turn, puts constraints on the possible rules by which targets can be chosen for spectroscopic observation. I will discuss some parts of this, including some simple results?rules to live by?and some open questions.

2019-07-19
15:00
Stellar Radial Velocity Jitter: A model free analysis and an introduction to the RV SPY survey
Stefan Brems (LSW)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)

2019-07-19
15:00
The Formation and Growth of Supermassive Black Holes at Early Cosmic Epochs
Anna-Christina Eilers (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
Quasars are the most luminous objects in the universe and can be observed at the earliest cosmic epochs, providing unique insights into the early phases of black hole, structure, and galaxy formation. Observations of these quasars demonstrate that they host supermassive black holes (SMBHs) at their center, already less than ~1 Gyr after the Big Bang. The formation and growth of these SMBHs in such short amounts of cosmic time is a crucial yet unanswered question in studies of quasar and galaxy evolution. An important piece of the puzzle is the lifetime of quasars ? the time that galaxies shine as active quasars ? but to date its value remains uncertain by several orders of magnitude. I will present a new method to obtain independent constraints on the lifetime of high redshift quasars, based on measurements of the sizes of the ionized regions around quasars, known as proximity zones. The sizes of these proximity zones are sensitive to the lifetime of the quasars, because the intergalactic gas has a finite response time to the quasars' radiation. Applying this method to a data set of high redshift quasar spectra at z>6, we discovered an unexpected population of very young quasars, indicating lifetimes of only ~10,000 years, which significantly challenges all current black hole formation theories. I will highlight the implications and tensions of such short quasar lifetimes on the SMBH formation paradigm, and discuss several potential modifications that could explain our results, for instance super-critical mass accretion rates, obscured quasar growth phases, or flickering quasar light curves. I will show potential ways to disentangle the various scenarios with future observations with the James Webb Space Telescope.

2019-07-12
15:00
Stellar Radial Velocity Jitter: A model free analysis and an introduction to the RV SPY survey
Stefan Brems (LSW)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
Stars show various amount of radial velocity (RV) jitter due to varying
stellar activity levels. I will show that by systematically analyzing
archival RV data with the pooled variance technique, one can quantify
this jitter as a function of age and observational timescale (lag). The
results yield a very strong dependence on the stellar age, ranging from
over 800 m/s for 3 Myr old stars down to the instrumental precision of
about 1.5 m/s for several Gyr old stars. Furthermore, the lag influences
the intrinsic stellar RV variation by about a factor of two when
probing a few days instead of weeks or years.
These results can for example be used to plan surveys where the age is a
major selection criterion. Being such a survey targeting young stars, I
will present the observational strategy as well as first results from
ongoing Radial Velocity Survey for Planets around Young stars (RV SPY)
using the FEROS spectrograph at the MPG/ESO 2.2m telescope.

2019-07-05
15:00
The Milky Way Laboratory
Cara Battersby (Uni of Conneticut)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
Our own Milky Way Galaxy is a powerful and relatively nearby laboratory in which to study the physical processes that occur throughout the Universe, from the organization of gas on galactic scales to the life cycle of gas and stars under varied environmental conditions. I will present a brief tour of our Milky Way Laboratory, including 1) the connection between long, filamentary molecular clouds and spiral structure, 2) statistical studies of high-mass star formation using surveys of our Galaxy's disk, and 3) how observing our extreme, turbulent Galactic Center (the Central Molecular Zone) can help us learn more about how gas is converted into stars during the peak epoch of cosmic star formation.

2019-06-28
15:00
MPIA space involvement
Oliver Krause & Knud Jahnke (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
Space-based observatories have brought a tremendous progress to astronomy over the past decades. From inaccessible wavelength bands in the X-ray, UV or infrared, to much improved sensitivities from lower backgrounds, to diffraction limited imaging above the atmosphere - there are a number of key differences to ground-based observing facilities.

MPIA has been a long-standing contributor to space-based telescopes and their instrumentation, as well as scientific user of space-generated data. We will give an overview of five new upcoming space observatories with MPIA hardware contributions: JWST, Euclid, WFIRST, SPICA, and HabEx. We will present their construction status and timelines, as well as the opportunities for MPIA science exploitation.

2019-06-21
15:00
Characterization of Planetary Atmospheres
Karan Molaverdikhani (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
Characterization of planetary atmospheres has always been a challenge. While the next generation of facilities, such as ELT, JWST, and ARIEL, will improve our understanding of planetary atmospheres, the number of well-characterized exoplanet atmospheres is expected to remain limited. Large-scale simulations assist us with this shortcoming by predicting the diversity of the planetary atmospheres, connecting the spare observational measurements, and by pointing toward the regions on the parameter space where a higher chance of the detection of planets with desired properties is expected. I will overview our current understanding of planetary atmospheres and will highlight the results of our hierarchical modelling of planetary atmospheres\; including our newly proposed classification scheme for irradiated gaseous planets and the Methane Valley.

2019-06-14
15:00
Gravitational instabilities: The fastest way to form planets
Hans Baehr (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
The early stages of circumstellar disk evolution are likely influenced by the relatively large gas mass, driving gravitational perturbations that result in turbulence and disk fragmentation. Fragmentation of the disk produces dense gaseous objects with masses on the order of a few Jupiter masses an up, and preferentially occurs in the cool distant regions of the disk. This provides a possible formation channel for directly imaged planets which are difficult to account for otherwise. Unfortunately, despite filling in this niche of planet formation, several factors make gravitational instabilites a minor factor in the overall planet formation paradigm. I will discuss the viability of gravitational instabilities as a planet formation theory, including recent developments in both observation and theory. These developments perhaps point away from the formation of massive gaseous planets and towards the early concentration of solid material in the vein of traditional core accretion models, but within the first million years of the lifetime of the disk.

2019-06-07
15:00
New approaches to stellar ages: Chronostar for kinematic ages, and Gaia+interferometric orbits for evolutionary ages
: Michael Ireland (ANU)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
One of the core goals of astrophysics is to determine the evolutionary history of stars, galaxies and the Universe. Unfortunately, there are few accurate determinations of ages of the Universe's constituents. I will describe new takes on two promising techniques for accurate stellar ages into the next decade. Firstly, I will describe the concept of ?traceback ages?, where stars from a common origin can have their ages determined by combining velocities with their distance from a common origin. This technique as largely failed so far, due to a myriad of reasons, including the rarity of unbound, compact clusters, and data where at least one kinematic axis has a large observational uncertainty. We have recently overcome these difficulties by combining the precision of Gaia data with Bayesian techniques and trace-forward of models in the Galactic potential, encompassed by the Chronostar code. We determine an age of beta Pic of 18.3+/-1.3 Myr, with an systematic uncertainty for individual members which is order the birth cluster crossing time of 12 Myr. I will describe the next steps for Chronostar, and where its limits are expected to lie. I will also briefly describe the problem of evolutionary ages for >1Gyr giant stars not part of a cluster. This is intimately connected to the controversy over the reported frequency of planets around ?retired A stars?. The combination of Gaia, long baseline interferometry and asteroseismology promises to significantly enhance our knowledge of these ages in the coming few years.

2019-05-24
15:00
Numerical experiments on star formation: mass functions and angular momenta
Lee Hartmann (UMich)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
The initial mass function of stars - the number of stars N formed per interval of mass M - has long been known to be a power law, with d log N/d log M = ? = -1.3. Many explanations of this distribution have been advanced over the years, including fractal dimensions of star-forming molecular clouds and/or self-similar grouping of clouds. I will discuss simplified numerical simulations of star formation which show that gravitational accretion onto initial seed masses generates a power law mass distribution approaching ? ? -1 asymptotically, irrespective of complications of cloud structure. This mechanism can also explain the mass function of young star clusters, which also has a power law distribution with ? = -1. Finally, I will describe preliminary results concerning the origin of protostellar cloud angular momenta, including magnetic fields, with implications for the properties of protoplanetary disks that result from cloud collapse.

2019-05-17
15:00
Early-type galaxies: climbing to the top of the mass ladder
Eric Emsellem (ESO)
Königstuhl Kolloquium
MPIA lecture hall,
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Abstract
Nearby galaxies display a range of morphologies, sizes, masses, which are the results of a complex set of formation and evolution processes. In this talk, I will focus on early-type galaxies which contain about half of all the stars in our local Universe.
I will review our current knowledge of how they form, what are the most important mechanisms which shaped them, and illustrate how our understanding of these objects changed over the last decade via the use of simulations and integral-field spectroscopy. I will then focus on the most massive galaxies, and report on results from numerical simulations and an observational campaign conducted with the MUSE spectrograph, which led to some interesting surprises.

2019-05-10
15:00
What Processes Shape our Milky Way's Disk?
Hans-Walter Rix (MPIA)
Königstuhl Kolloquium
MPIA lecture hall,
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Abstract
It is often said that the Milky Way can serve as a 'model organism' to explore and understand the physical mechanism that shape galaxies from random initial fluctuations into the beautiful island universes we see today. This statement is true, but easily said and much harder to make a reality. Over the last years I have collaborated with a number of students, post-docs and visitors at MPIA combining spectral surveys and now Gaia to turn this Galactic Archeology mantra into astrophysical insights. In this talk I will synthesize some of this effort, focussing on two aspects of our Galaxy's main component, its disk:
what sets the overall radial profile of the disk, and what sets its vertical structure? The answers to both questions are linked to the question of how much dynamical memory loss our Galaxy has incurred -- despite its exceptionally quiescent history. I believe we are now considerably closer to understanding why disk galaxies look the way they do.

2019-05-03
15:00
Exocometary Science
Luca Matrà (CfA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
Evidence for exocomets, icy bodies in extrasolar planetary systems, has rapidly increased over the past decade, giving rise to the budding field of exocometary science. Exocomets are detected through the gas and dust they release as they collide and grind down within their natal belts, or as they sublimate once scattered inwards to the regions closest to their host star. Most detections are in young, 10 to a few 100 Myr-old systems that are undergoing the final stages of terrestrial planet formation. This opens the exciting possibility to study exocomets at the epoch of volatile delivery to the inner regions of planetary systems.

In this talk, I will present the different lines of evidence for exocomets from UV to mm wavelengths. In particular, I will show how detection of molecular and atomic gas allows us to estimate molecular ice abundances and elemental abundances in young exocomets, enabling comparison with the Solar Nebula and Solar System comets. Finally, I will link the composition of exocometary belts to their origins in protoplanetary disks, discussing evidence for a preferential belt formation location which is dependent on the host star's luminosity.

2019-04-26
15:00
From dense cores to disk: Following the gas
Jaime Pineda (MPE)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
A detailed understanding of star-formation is important to establish the "micro-physics" involved in the galactic star-formation relations, and also to determine the initial condition for proto-planetary disks. One of the important steps in the star-formation process is the accumulation of material from the molecular cloud with supersonic turbulence into the dense cores, which have subsonic turbulence. The first direct observation of the transition between supersonic and subsonic turbulence in a nearby cloud provided the first direct constraints on this dissipation process. On the other hand, recent observations have shown that large protoplanetary disks in the early stages are relatively rare, and for those that are large, there is compelling evidence for asymmetries related to gravitational instabilities. However, little is known of the connection between the disks and the parental dense core.

In this talk, I will present some of our latest efforts on studying the dense core and molecular cloud connection, thanks to a large program at the Green Bank Telescope (~250hrs, PIs: Jaime Pineda and Rachel Friesen). This survey allows us to more accurately determine the dense core properties in a systematic fashion and across several clouds. Also, I will present interferometric observations of dense cores that will provide new insight into the core formation and the material transport down to the scales relevant for disk formation.

2019-04-12
15:00
The Brightest Stars in the Universe as Extragalactic Probes of Cosmic Abundances and Distances
Rolf-Peter Kudritzki (IFA,USM)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
The determination of chemical composition and distance is crucial for investigating the formation and evolution of star-forming galaxies. Stellar absorption line studies based on quantitative spectroscopy provide an attractive alternative to the standard techniques using the strong emission lines of HII regions for chemical composition or stellar photometric methods for distances. I will introduce a number of newly developed methods
- multi-object spectroscopy of individual blue and red supergiant stars, the brightest
stars in the universe at visual and NIR wavelengths,
- NIR spectroscopy of super star clusters,
- optical spectroscopy of the integrated light of stellar populations in the disks of star
forming galaxies,
- the flux-weighted gravity luminosity relationship for distance determinations
and present results accumulated in the last two years. I will then discuss the scientific perspectives and potential of these methods for the use of future Extremely Large Telescopes (ELTs).

2019-04-05
15:00
The multi-phase ISM of radio galaxies: a spectroscopic study of ionised and warm gas
Francesco Santoro (MPIA)
Königstuhl Kolloquium
MPIA lecture hall,
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Abstract
Active galactic nuclei (AGN) are among the most powerful sources of energy in the universe. They usually resides at the centre of massive galaxies and their energy is originated by the accretion of material onto a supermassive black hole. AGN can inject a significant amount of energy in the interstellar medium (ISM) of their host galaxies in the form of radiation and/or jets of relativistic particles. The interaction between the energy emitted by an AGN and the material in the host galaxy is called 'AGN feedback' and, nowadays, is routinely included in cosmological simulations aimed at reproduction the observed properties of the current population of galaxies (e.g. the quenching of the star formation in massive galaxies).

In this talk I will address some of the open questions related to AGN feedback and to the mechanisms involved in the accretion of gas onto a supermassive black hole. This is has been done by studying the ISM of radio galaxies (i.e. AGN showing relativistic jets) spanning different evolutionary stages and by using different observational techniques, mainly in the optical and in the infrared band, to probe the warm ionised and warm molecular gas. In particular, I will focus on the effect that radio jets can have on the gas of the host galaxy and how this allows us to take a look at the many facets of the AGN feedback phenomenon.

2019-03-29
15:00
TBA
Paola Di Matteo (GEPI/Obs. de Paris)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
Signature Speaker

2019-03-22
15:00
Paola Di Matteo (GEPI/Obs. de Paris)
: Signature Speaker
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)

2019-03-22
15:00
Paola Di Matteo (GEPI/Obs. de Paris)
: Signature Speaker
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)

2019-03-22
15:00
Probing the cold phase of the interstellar medium and star formation in nearby galaxies
Neven Tomicic (MPIA)
Königstuhl Kolloquium
MPIA lecture hall,
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Abstract
Properly measuring the spatial distribution of the star formation rate (SFR) in nearby galaxies helps us to understand the driving forces for the star formation in galaxies, and their effects on the interstellar medium (ISM). Additionally, it can lead to better understanding the physical factors that set the efficiency with which galaxies convert gas into stars (star formation efficiency\; SFE), and their role in galactic evolution. However, this is hindered by the uncertainties in estimating SFRs and calibrating the SFR prescriptions. Furthermore, variations in the star formation efficiency between and within galaxies are difficult to disentangle from uncertainties of their estimated SFRs. The uncertainties in estimating SFRs are caused by not properly measuring the attenuation of light, probing large spatial scales across nearby galaxies, or averaging over a large sample of galaxies.
To bypass these uncertainties, common SFR prescriptions are used, which also have large uncertainties and variations.

In this talk, I will show how we utilize optical integral field unit (IFU) observations of the nearby Andromeda galaxy, in order to properly measure the attenuation of light at high spatial resolution (100 pc), and thus properly estimate the SFRs and the SFR prescriptions. Moreover, by using the results of our optical IFU and sub-mm observations of the interacting galaxy NGC 2276, I will show how the early phase of galactic interaction affects the star formation efficiency of molecular gas across the interacting galaxy.

2019-03-22
09:45
The Milky Way as a dark matter lab
Jorge Penarrubia (ROE)
Königstuhl Kolloquium
MPIA lecture hall,

2019-03-21
09:45
A modern theoretical framework for the cosmic evolution of galactic emission lines
Michaela Hirschmann (U. Vienna, Dark Center)
Königstuhl Kolloquium
MPIA lecture hall,

2019-03-20
10:30
Numerical Structure and Galaxy Formation for Cosmological Insight
Annalisa Pillepich (MPIA)
Königstuhl Kolloquium
MPIA lecture hall (TBC),

2019-03-19
09:45
Intergalactic Signatures of Reionization and the Growth of the First Supermassive Black Holes
Frederick Davies (UC Santa Barbara)
Königstuhl Kolloquium
MPIA lecture hall,

2019-03-18
09:45
The Milky Way as a laboratory on galaxy formation and dark matter
Chervin Laporte (U. Victoria)
Königstuhl Kolloquium
MPIA lecture hall,

2019-03-15
15:00
"Milky Way dust in 3D: from local molecular clouds to the spiral arms"
Sara Rezaei Kh. (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract

Milky Way dust in 3D: from local molecular clouds to the spiral arms

Only a tiny fraction of the mass of the Galaxy is in dust, yet it plays important roles in different processes\; from the formation of stars and planets to the luminosity of the Galaxy. Attempts to map our Milky Way date back to the 18th century, but we are still struggling to find an accurate picture of our Galaxy as a result of our obscured view within the dusty disk. In this talk, I will give you a general introduction to dust and extinction, followed by a summary of the improvements in 3D dust extinction mapping. I will then introduce our new technique in mapping the 3D distribution of dust in the Milky Way using the Gaussian process that allows capturing arbitrary structures and results in smooth maps without artefacts typically seen in most other methods. I will show our results based mainly on data from Gaia and APOGEE for the local molecular clouds as well as the Galactic disk, where we unveil the distribution of the spiral arms of the Milky Way in dust.

2019-03-08
15:00
Science with VLTI+GRAVITY
Woflfgang Brandner (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
GRAVITY is a 4-telescope beam combiner for ESO's Very Large Telescope Interferometer (VLTI), working in the K-band. While the instrument design has been optimized for high-precision observations of the Milky Way's central supermassive black hole Sgr A* and its immediate environment, the unique sensitivity of VLTI+GRAVITY enable a large range of science applications.

In this talk, I will briefly describe the main capabilities and technological innovations of GRAVITY, which includes the four CIAO (one for each of the 8m-Unit Telescopes) infrared adaptive optics systems provided by MPIA, followed by a concise overview of science results obtained during GRAVITY commissioning and the first 1.5 years of regular science operations at the VLTI. The science topics range from the atmosphere of the exoplanet HR 8799e over properties of disks and outflows in the central AU of Young Stellar Objects, multiplicity of stars in the center of the Orion Nebula Cluster, resolution of microlensed images, spectral-imaging of the close environment of Eta Carinae, and observations of Galactic X-ray binaries, to the study of relativistic effects in the Galactic Center, and a direct measurement of the mass of the supermassive blackhole in the center of the quasar 3C 273.

2019-03-01
15:00
TBA
: Sara Rezaei Kh. (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)

2019-03-01
15:00
TBA
Marcel Neeleman (MPIA)
Königstuhl Kolloquium
MPIA lecture hall,

2019-02-22
15:00
Stellar populations in the densest stellar systems in the Universe
Nikolay Kacharov (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
In this talk I will introduce some of the open questions in the field of globular clusters and nuclear star clusters. As one part of the colloquium, I will talk about the multiple populations phenomenon in globular clusters and focus on our recent discoveries in intermediate age clusters in the Magellanic Clouds. The second part will be dedicated to the much more extended star formation histories in nuclear star clusters. I will discuss our discrete IFU spectroscopic observations of the nucleus of the tidally disrupted Sgr dSph galaxy - the massive globular cluster M54, and also integrated light spectroscopy in the nuclei of yet undisturbed nearby galaxies. I will explore and discuss possible theories for the formation of these very dense objects based on our observations.

2019-02-15
15:00
The Cosmic Evolution of Cold Molecular Gas since Redshift 6 from A3COSMOS
Daizhong Liu (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
Determining the cosmic evolution of cold molecular gas in galaxies is fundamental for our understanding of galaxy evolution. However, obtaining such measurements for large samples of galaxies at z~1--6 remains challenging even in the era of ALMA. Recent studies of the cosmic gas evolution focus on redshifts below z=3 reporting conflicting results, and cosmological simulations still struggle to fit the observations. As (sub-)millimeter dust continuum has now been established as a reliable tracer of the cold gas, and it can be much more efficiently observed than line tracers (e.g. CO), we have started a concerted effort to automatically mine the public ALMA archive for the COSMOS field (A3COSMOS). A3COSMOS provides (sub-)millimeter detections and subsequent galaxy properties in a coherent, systematic way that allows us to quantify systematic biases in using dust continuum. Our database currently includes about 2000 ALMA images covering 280 sq. arcmin with over 1500 ALMA detections based on well-characterized statistics. Using rich ancillary data available we identify ~1000 galaxies with bona-fide properties lying at z~1--6. We combine this unique catalog of cold gas measurements with more than 500 local (z~0) and high-redshift (z<3) galaxies with CO and/or dust continuum detections in the literature to explore the correlations between gas mass fraction, molecular gas depletion time, redshift, stellar mass and star formation rate. Our analysis reveals a linear evolution of the gas fraction with cosmic time, in line with the evolution of the ?galaxy main sequence?. This evolution further implies a cosmic molecular gas density evolution consistent with previous works at z<1-3, but higher by a moderate factor at z>5--6 as predicted by cosmological simulations. As ALMA accumulates more observations in the future, the cold molecular gas evolution at z>5--6 will eventually be constrained by A3COSMOS.

2019-02-08
15:00
Dust Spreading in Debris Discs: Do Small Grains Cling on to Their Birth Environment?
Nicole Pawellek (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
Debris discs are dusty belts of planetesimals around main-sequence stars, similar to comets and asteroids in the solar system. The planetesimals themselves cannot be observed directly, yet they produce detectable dust in mutual collisions. Observing this debris dust, we can try to infer properties of invisible planetesimals. Here we address the question of what is the best way to measure the location and extent of outer planetesimal belts, i.e., ''Kuiper belts'' that encompass extrasolar planetary systems. A standard method is using resolved images at millimetre wavelengths, which reveal dust grains of comparable sizes. This is because smaller dust particles seen in the infrared or optical are subject to a large array of non-gravitational forces that drag them away from their birth places, and so may not closely trace the parent bodies. In this study, we examine whether imaging of debris discs at shorter, far- or even mid-infrared, wavelengths might enable determining the spatial location of the exo-Kuiper belts with sufficient accuracy. We find that around M-type stars the dust best visible in the mid-infrared is efficiently displaced inward from their birth location by stellar winds, causing the discs to look more compact in the mid-infrared images than they actually are. However, around A-type stars, where the majority of debris discs is found, and even around G-type stars, discs are still the brightest at the location of the birth ring at mid-infrared wavelengths. Thus, sensitive infrared facilities with good angular resolution, such as MIRI on the James Webb Space Telescope, will enable tracing exo-Kuiper belts in nearby debris disc systems.

2019-02-01
15:00
Stellar Interiors as seen from Asteroseismology
Conny Aerts (U. Leuven)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
The space age of asteroseismology brought tremendous progress in the
observational probing of stellar interiors. In this seminar, we first explain
for the non expert how asteroseismology allows to deduce the interior physics of
stars at a level that is impossible to reach in any other way. We summarise the
great asset of asteroseismic sizing, weighing, and ageing of low-mass stars,
with applications to exoplanetary science and galactic archeology. Further, we
focus on the capability to derive the interior rotation properties of various
types of stars and discuss the implications for the theory of angular momentum
transport. We also touch upon recent findings on chemical mixing in the deep
interior of single and binary stars with a convective core. We end the talk by
highlighting the major opportunities from combining space asteroseismology and
astrometry with ground-based spectroscopy of large ensembles of stars in the
Milky Way and in the Magellanic Clouds.

2019-01-25
15:00
Giant Molecular Filaments studied in different gas tracers
Yuan Wang (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
Observations show that large (~100~pc) and massive (~10^5 Msun) filaments, known as giant molecular filaments (GMFs), may be linked to galactic dynamics and trace the gravitational mid-plane in the Milky Way (MW). They are the largest coherent gas structures and a central building block of the Milky Way. Yet our understanding of GMFs is still poor, limited to estimates of their occurrence, gas masses and lengths. In this talk, I will present our studies of two GMFs (GMF38a and GMF54), which are observed with different gas tracers (atomic and molecular). We studied the cold neutral media of atomic hydrogen via HI self-absorption towards the ~200pc long filament GMF38a, and compared the kinematics and column density distribution of the atomic hydrogen to the molecular gas (CO). The column density probability density functions (N-PDFs) show that the atomic gas is dominated by turbulent motions, whereas the N-PDF of the molecular gas shows a power-law tail that indicates gravitational collapse. We further mapped the dense gas of GMF54 (~45pc) with the IRAM 30m telescope, covering the common dense gas tracers HCN, HNC, HCO+ and their 13C isotopologues, as well as the cold dense gas tracer N2H+. Combining the complementary 13CO data, we studied and compared the kinematics and the density distribution of GMFs over an order of magnitude in density.

2019-01-18
15:00
Star Formation and Galactic Environment
Eva Schinnerer (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
High angular resolution observations of nearby galaxies allow us to sample the star formation process in different galactic environments.This provides insights on the importance and role of galactic components such as bulges, stellar bars, spiral arms and active galactic nuclei (AGN) in the conversion of cold (molecular) gas into stars. New instruments can now regularly image with high quality and sensitivity large field-of-views
at the scale of individual star-forming units, namely Giant Molecular Clouds (GMCs) and HII region (complexes): ALMA is fundamental for imaging of the molecular gas properties in the star-forming disks, while the optical Integral Field Unit MUSE on the VLT is providing detailed information on the ionised gas and stellar population. I will highlight recent progress in the field and present new results from the Physics at High Angular resolution in Nearby GalaxieS (PHANGS) survey that studies a representative sample of nearby massive, normal star-forming galaxies.

2019-01-11
15:00
The Disk Substructures at High Angular Resolution Project (DSHARP)
Kees Dullemond (ITA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
Abstract: DSHARP is an ALMA Large Programme aimed at obtaining high-resolution (beam ~ 30 milliarcsec) maps of 20 protoplanetary disks in band 6 (1.3 mm) in the continuum. The data were released about a month ago, along with a first set of papers. I will give an overview of the data and some of the gems hidden in them. I will then focus on the theoretical interpretation that the DSHARP team has done, and many of the still open questions that need to be addressed in the coming months.

2018-12-14
15:00
TBA
Karin Lind (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
TBA

2018-12-14
15:00
Lithium in the Galaxy: To Be or not to Be
Karin Lind (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
The astronomical community's interest in Li continues to be vastly disproportional to its small abundance. The Li content of stars in the Galaxy links together several different research fields\; from cosmology and Big Bang nucleosynthesis, to cosmic ray spallation in the interstellar medium, to mixing processes in stellar interiors, and even the presence of exoplanets. I will describe the intricate abundance patterns found for stars in different evolutionary phases and how the fragile nature of this light element makes it an excellent diagnostic tool for late-type stellar evolution all they way from the pre-main sequence to the tip of the asymptotic giant branch. I will further discuss some famous problems related to Li production and depletion and potential solutions in the light of improved models of stars and their spectra.

2018-12-07
15:00
TBD
HHSF18
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
TBD

2018-12-07
15:00
The Square Kilometer Array
Tyler Bourke (SKAO)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
The Square Kilometre Array (SKA) is a global effort to build the World's largest radio telescopes, which will transform our understanding in many areas of astrophysics, including the history of our Universe and the emergence of the first stars and galaxies\; the merger of super-massive black-holes and their release of gravitational waves, as tests of General Relativity\; the enigmatic powerful bursts of radio emission (Fast Radio Bursts) whose origin and nature remain controversial\; the formation of planets and search for extraterrestrial life\; and many other areas of great interest to astronomers worldwide.

The past few years have seen great progress toward the realization of the SKA, with construction of Phase 1 (SKA1) to start in 2020 and science operations anticipated to begin in 2026. In this presentation I will provide a status update on SKA activities, with a focus on the science it will enable and the progress toward construction.

2018-11-30
15:00
Patzer Colloquium
TBA (TBA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)

2018-11-30
15:00
Three award winners
Patzer Colloquium (MPIA+ZAH)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)

2018-11-23
15:00
TBD
Bertram Bitsch (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
TBD

2018-11-23
15:00
Planet formation in evolving protoplanetary discs
Bertram Bitsch (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
Observations of exoplanets have revealed a complex diversity in planetary systems regarding their masses, orbital configurations and number of planets. For example it has been shown that super-Earth planets are the most common planets in our galaxy even though we have no super-Earth in our own solar systems and that these planets are mostly in multiple systems. Hot Jupiters, on the other hand, are easy to detect, but are actually very rare objects. In addition new observations give indications about the chemical compositions of these planets. All these constraints have to be matched by theories of planet formation.

The formation of planetary cores of several Earth masses can be greatly accelerated by accreting objects of mm-cm size, so called pebbles. When the planetary cores have reached masses around 10 Earth masses, they can start to accrete gas from the protoplanetary disc and eventually form gas giants, like Jupiter and Saturn in our own solar system. During their formation, the planetary cores interact gravitationally with the disc and migrate through it. At the same time the protoplanetary disc evolves so that its temperature decreases, resulting in an inward movement of the water ice line. Previous simulations have also mostly followed the evolution of single planets, where multi-body dynamics have been ignored.

I will present here our new framework of planet formation that features a complex interplay between N-body dynamics, pebble accretion, planet migration, disc evolution and planetary instabilities after the gas disc phase. I will highlight the results of our new simulations and point to open questions that need to be answered in order to constrain planet formation theories even further.

2018-11-16
15:00
TBD
Rowan Smith (University of Manchester)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
TBD

2018-11-16
15:00
Filaments all the way down: Simulating molecular gas in the Milky Way
Rowan Smith (University of Manchester)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
The process of star formation and galaxy evolution are inseparably linked. Stars feed back energy and momentum into the ISM, but galactic scale forces will help determine where dense star-forming molecular clouds can form. Previously star formation was simulated only in isolation, and galaxy scale models did not resolve star forming clouds, however recent simulation efforts have begun to unite these important physical processes. Observations have also shown us that molecular clouds are far from the abstracted collapsing spherical clouds or periodic turbulent boxes used to model them previously. Instead many clouds take the form of long filaments with extremely coherent velocities.

In this talk I present simulations exploring the morphology and star formation in filamentary molecular clouds from spiral galaxy simulations with AREPO. The clouds are resolved down to sub-parsec scales in the original simulation meaning, uniquely, that both galactic-scale forces and internal cloud substructure can be studied at the same time. The simulations include supernovae feedback, self-gravity, time-dependent chemistry and sinks particles to represent sites of star formation. This allows us to study the evolution of the CNM, where gas will be bright in CII or CO emission, and where there will be CO dark gas.

Using this dataset we can extract filamentary clouds and compare their lengths and widths against observations of arm and inter-arm filaments observed in our Galaxy. Within our simulated clouds we identify networks of dense filaments connecting star forming gas cores. Previous analysis of such networks of filaments in isolated turbulent molecular cloud cores. has shown that the mass flows along filaments play a key role in building up a stellar initial mass function, and in growing massive stars.

2018-11-09
15:00
The base material of terrestrial planets - investigating the dust in the inner region of protoplanetary disks
Lucia Klarmann (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
The inner regions of protoplanetary disks are where terrestrial planets and super-Earths form and/or migrate to. The small spatial extend of this region makes direct observations difficult. But interferometric observations and dust modeling can put constraints on the base material of terrestrial planet formation.

We self-consisently calculate the expected rim structure for a wide range of possible dust compositions. Synthetic observations of these radiative transfer models show that the rim position can be well constrained using NIR interferometry. Comparing our rim positions with observations from Lazareff+17, we find that the observed positions can be explained by a power law grain size distribution, but also the presence of highly refractory grains.

Motivated by the low carbon fraction in the Earth, we investigate how to sustain a low fraction of refractory carbon in the inner disk. We find that radial dust transport in the disk must be significantly reduced during parent body formation, possibly by a quickly formed giant planet core. Otherwise grains from the outer disk region will replenish refractory carbon very efficiently within the grain drift timescale.

2018-10-26
15:00
TBD
Mario Flock (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
TBD

2018-10-26
15:00
The Inner Regions of Protoplanetary Disks: 3D Radiation Magneto-Hydrodynamical Models
Mario Flock (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
Many planets orbit within an AU of their stars, raising questions about their origins. Particularly puzzling are the planets found near the silicate sublimation front. We investigate conditions near the front in the protostellar disk around a young intermediate-mass star, using the first global 3D radiation non-ideal MHD simulations in this context.

The results show magnetorotational turbulence around the sublimation front at 0.5 AU. Beyond 0.8 AU is the dead zone, cooler than 1000 K and with turbulence orders of magnitude weaker. A local pressure maximum just inside the dead zone concentrates solid particles, allowing for efficient growth. Over many orbits, a vortex develops at the dead zone's inner edge, increasing the disk's thickness locally by around 10%.

We synthetically observe the results using Monte Carlo transfer calculations, finding the sublimation front is bright in the near-infrared. The models with vertical magnetic flux develop extended, magnetically-supported atmospheres that reprocess extra starlight, raising the near infrared flux 20%. The vortex throws a non-axisymmetric shadow on the outer disk.

Radiation-MHD models of the kind we demonstrate open a new window for investigating protoplanetary disks' central regions. They are ideally suited for exploring young planets' formation environment, interactions with the disk, and orbital migration, in order to understand the origins of the close-in exoplanets.

2018-10-19
15:00
TBD
Michael Rugel (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
TBD

2018-10-19
15:00
OH abundance and feedback from star clusters with the THOR survey
Michael Rugel (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
In this colloquium, I present characterizations of molecular cloud properties with the THOR survey (The HI, OH and Radio Recombination Line (RRL) survey of the Milky Way). We analyze OH absorption at 18 cm within THOR and follow-up observations. We derive the abundance with respect to molecular hydrogen and the total number of hydrogen nuclei: 1) We find a decreasing OH abundance with increasing column density of molecular hydrogen. 2) Due to significant column densities of atomic hydrogen at low OH column density, the OH abundance with respect to the column density of hydrogen nuclei is approximately constant. 3) We detect OH components which are associated with gas that is not predominantly molecular or even CO-dark. We conclude that OH is a potential tracer for diffuse gas.
Regarding the impact of star clusters on molecular clouds, we detect signatures of feedback in RRL emission in the star forming region W49A. A comparison to the WARPFIELD models (one-dimensional models of feedback-driven shells) indicates that feedback is not yet strong enough to disperse its molecular cloud and that the shell is either in process of re-collapsing to initiate a new event of star formation or has already re-collapsed. This suggests that at least parts of the star formation in W49A is regulated by feedback.

2018-10-12
15:00
TBD
Fei Yan (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)

2018-10-12
15:00
Transit spectroscopy of exoplanet atmospheres
Fei Yan (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
With almost 4000 exoplanets been discovered, characterizing their atmospheres becomes a rapidly expanding branch in exoplanet research. In this talk, I will focus on transit spectroscopy ? the most commonly used method for atmosphere observations. This method has been successfully applied to discover various chemical species (e.g. water, carbon monoxide, sodium) as well as to characterize psychical conditions like temperature profile and wind. I will present results of our transit observations with CARMENES and MODS/LBT spectrographs, including probing the atmosphere of the hottest exoplanet - KELT-9b. In addition, I will also talk about how the variation of stellar line profiles during transit will affect exoplanet atmosphere observations.

2018-10-05
15:00
TBA
PSF signature speaker Sarah Hörst (JHU)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)

2018-10-05
15:00
Exploring Planetary Atmospheres in a Lab
PSF signature speaker Sarah Hörst (JHU) : Planets in a Bottle
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
From exoplanets, with their surprising lack of spectral features, to Titan and its characteristic haze layer, numerous planetary atmospheres may possess photochemically produced particles of "haze". With few exceptions, we lack strong observational constraints (in situ or remote sensing) on the size, shape, density, and composition of these particles. Photochemical models, which can generally explain the observed abundances of smaller, gas phase molecules, are not well suited for investigations of much larger, solid phase particles. Laboratory investigations of haze formation in planetary atmospheres therefore play a key role in improving our understanding of the formation and composition of haze particles. I will discuss a series of experiments aimed at improving our understanding of the physical and chemical properties of planetary atmospheric hazes on Titan, Pluto, super-Earths, and mini-Neptunes.

2018-09-28
15:00
The Intricate Role of Cold Gas and Dust in Galaxy Evolution at Early Cosmic Epochs
Dominik Riechers (Cornell, MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
Great progress has been made over the past two decades in constraining
the star formation history of the universe, but our understanding of
how cosmic star formation is fuelled by cold gas at high redshift is
currently informed primarily by specific, and potentially biased
samples of galaxies. To overcome these limitations, we have carried
out the CO Luminosity Density at High Redshift (COLDz) survey, a large
blind volume search for cold molecular gas in galaxies at redshifts
2-3 and 5-7 with the Karl G. Jansky Very Large Array (VLA). The
resulting measurement of the "cold gas history of the universe" near
the peak epoch of cosmic star formation and in the first billion years
of cosmic time provides important information on the fuelling
mechanisms that drive cosmic star formation. Surveys like COLDz set
the necessary broader context for targeted in-depth studies of the
physical properties of star formation in different galaxy populations
back to the earliest epochs with the Atacama Large sub/Millimeter
Array (ALMA). Such studies fundamentally enhance our picture of early
galaxy evolution by providing a better understanding of the stellar
mass buildup, and they are a critical pathfinder toward galaxy surveys
in the early universe with upcoming large facilities, in particular
the next generation Very Large Array (ngVLA).

2018-09-28
15:00
Evolution of Gas Content Through Cosmic History
Fabian Walter (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
The temporal evolution of the cosmic star formation rate density is now well established out to high redshift. This star formation rate density shows a clear peak at z~1-2 that is about one order of magnitude higher than today. The cause for this behavior must be driven by the properties of the underlying reservoir of molecular gas, the fuel for star formation galaxies. The last decade has seen dramatic progress in quantifying the molecular gas content in galaxies through cosmic times, through various observational camapigns. I will summarize our current view of the molecular gas content in distant galaxies. This will include some of the recent results emerging from ASPECS: The ALMA SPECtroscopic Survey in the Hubble Ultra-Deep Field (UDF). This ALMA large program provides a census of molecular gas in high-redshift galaxies through full frequency scans at approximately uniform line sensitivity. The resulting cosmic molecular gas density as a function of redshift shows a factor 3-10 decrease from z=2 to z=0. The cosmic star formation history therefore appears to be at least partly driven by the increased availability of molecular gas reservoirs at the peak of cosmic star formation (z~2).

2018-09-21
15:00
The World Beyond the Snow Line: Microlensing Comes of Age
Andy Gould (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
Microlensing is orthogonal to all other planet-search techniques. First, its sensitivity to planets peaks just beyond the snowline, where planets are thought to be most common. Second, it is roughly equally sensitive to planets around all stars, independent of their luminosity, and even to planets that have no host. Third, it is roughly equally sensitive to planets at a range of distances from 1 to 8 kpc. These features potentially enable microlensing to cast a radically different light on planetary demographics. I discuss how the 10-fold increase in microlensing data provided by the Korea Microlensing Telescope Network (KMTNet) and "microlens parallax" observations with the Spitzer Space Telescope are rapidly unleashing this potential.

2018-09-21
15:00
The World Beyond the Snow Line: Microlensing Comes of Age
Andy Gould (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
Microlensing is orthogonal to all other planet-search techniques. First, its sensitivity to planets peaks just beyond the snowline, where planets are thought to be most common. Second, it is roughly equally sensitive to planets around all stars, independent of their luminosity, and even to planets that have no host. Third, it is roughly equally sensitive to planets at a range of distances from 1 to 8 kpc. These features potentially enable microlensing to cast a radically different light on planetary demographics. I discuss how the 10-fold increase in microlensing data provided by the Korea Microlensing Telescope Network (KMTNet) and "microlens parallax" observations with the Spitzer Space Telescope are rapidly unleashing this potential.

2018-09-14
15:00
Quantifying and understanding variations in star formation
Sami Dib (NBI)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
Star formation is a multi-physics, multi-scale process. The multiplicity of physical processes and scales can generate a significant amount of scatter in the outcome of star formation, in particular in terms of key quantities such as the stellar initial mass function (IMF), the star formation rate (SFR), and the star formation efficiency (SFE). By analyzing large data sets that are becoming increasingly available, one can now assess whether variations do actually exist, quantify them, and attempt to explain them via a comparison with (a range of) theoretical models. I will illustrate this by presenting examples related to the IMF in young Galactic stellar clusters and to the star formation scaling relations in nearby galaxies. I will show that current data argues against a universal IMF in Galactic stellar clusters. I will also argue that the star formation scaling relations on galactic scales should include a description of the role of several other physical quantities, instead of being understood in terms of a mere dependence of the SFR on the density of the star forming gas.

2018-09-14
15:00
Quantifying and understanding variations in star formation
Sami Dib (NBI)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
Show/hide abstract

Abstract
Star formation is a multi-physics, multi-scale process. The multiplicity of physical processes and scales can generate a significant amount of scatter in the outcome of star formation, in particular in terms of key quantities such as the stellar initial mass function (IMF), the star formation rate (SFR), and the star formation efficiency (SFE). By analyzing large data sets that are becoming increasingly available, one can now assess whether variations do actually exist, quantify them, and attempt to explain them via a comparison with (a range of) theoretical models. I will illustrate this by presenting examples related to the IMF in young Galactic stellar clusters and to the star formation scaling relations in nearby galaxies. I will show that current data argues against a universal IMF in Galactic stellar clusters. I will also argue that the star formation scaling relations on galactic scales should include a description of the role of several other physical quantities, instead of being understood in terms of a mere dependence of the SFR on the density of the star forming gas.

2018-09-07
15:00
Magnetic Fields ? Polarization ? Disks
Gesa Bertrang (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
Magnetic fields are predicted to be an important factor for a wide range of physical processes in protoplanetary disks. In the classical picture, (sub-)mm continuum polarization is the tracer for magnetic fields in disks. Aspherical dust grains, whose thermal emission is intrinsically polarized, get aligned by the magnetic field due to radiative torques. In recent years, however, this picture has been challenged. New theoretical studies show that (sub-)mm continuum polarization can also be created by scattering of the thermal dust emission or arise from aspherical grains which are aligned by the radiation field rather than the magnetic field. These three mechanisms trace fundamentally different physics in protoplanetary disks, yet, their polarization predictions are not clearly distinguishable. In this talk, I will highlight the role of magnetic fields in protoplanetary disks, present already achieved (indirect) observational constraints, and give an outlook on how to disentangle the sources of continuum polarimetry with ALMA by applying spectro-polarimetry.

2018-09-07
15:00
Magnetic Fields ? Polarization ? Disks
Gesa Bertrang (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
Magnetic fields are predicted to be an important factor for a wide range of physical processes in protoplanetary disks. In the classical picture, (sub-)mm continuum polarization is the tracer for magnetic fields in disks. Aspherical dust grains, whose thermal emission is intrinsically polarized, get aligned by the magnetic field due to radiative torques. In recent years, however, this picture has been challenged. New theoretical studies show that (sub-)mm continuum polarization can also be created by scattering of the thermal dust emission or arise from aspherical grains which are aligned by the radiation field rather than the magnetic field. These three mechanisms trace fundamentally different physics in protoplanetary disks, yet, their polarization predictions are not clearly distinguishable. In this talk, I will highlight the role of magnetic fields in protoplanetary disks, present already achieved (indirect) observational constraints, and give an outlook on how to disentangle the sources of continuum polarimetry with ALMA by applying spectro-polarimetry.

2018-08-10
15:00
Fitting a model to data, 2018 edition
David Hogg (NYU, MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
I use examples from the Gaia Mission to illustrate ideas behind the theory and best practices for fitting a model to data. I will address (a) accounting for noisy data and selection effects, (b) dealing with outliers, and (c) model selection and deciding among models. I use very simple models (like straight lines!) and Gaia data for my examples, but the rules I give ? which are designed to minimize the loss of information ? are applicable at all model complexities and in all domains.

2018-08-10
15:00
Fitting a model to data, 2018 edition
David Hogg (NYU, MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
I use examples from the Gaia Mission to illustrate ideas behind the theory and best practices for fitting a model to data. I will address (a) accounting for noisy data and selection effects, (b) dealing with outliers, and (c) model selection and deciding among models. I use very simple models (like straight lines!) and Gaia data for my examples, but the rules I give ? which are designed to minimize the loss of information ? are applicable at all model complexities and in all domains.

2018-08-03
15:00
Mind the gap: swimming the channels between islands of popular star formation research
Joe Mottram (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
Like most sub-fields, star formation research has it's popular topics for research. Current examples include searching for structure in disks around low or high-mass protostars, and studying filaments in molecular clouds. I will present research from three projects, each of which aimed to make progress on our broader understanding of the star formation process and ISM lifecycle by exploring the space between these popular islands of research. First, I will present studies of thermal H2O and CO transitions observed towards a sample of low, intermediate and high-mass young stellar objects in order to explore the differences and similarities between low and high-mass protostars. This project ultimately led to a surprising alternative explanation for the emission in such transitions from external galaxies. Second, I will show observational studies of ionised pillars with CARMA, ALMA and MUSE, and how these are helping to constrain models of how these iconic structures are formed. Finally, I will discuss part of my work here at the MPIA combining single-dish and interferometric data to link sites of high-mass star formation with their surroundings. Taken together, these projects reveal the value of striking our into new territory by exploring the space between our islands of knowledge.

2018-08-03
15:00
Mind the gap: swimming the channels between islands of popular star formation research
Joe Mottram (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
Show/hide abstract

Abstract
Like most sub-fields, star formation research has it's popular topics for research. Current examples include searching for structure in disks around low or high-mass protostars, and studying filaments in molecular clouds. I will present research from three projects, each of which aimed to make progress on our broader understanding of the star formation process and ISM lifecycle by exploring the space between these popular islands of research. First, I will present studies of thermal H2O and CO transitions observed towards a sample of low, intermediate and high-mass young stellar objects in order to explore the differences and similarities between low and high-mass protostars. This project ultimately led to a surprising alternative explanation for the emission in such transitions from external galaxies. Second, I will show observational studies of ionised pillars with CARMA, ALMA and MUSE, and how these are helping to constrain models of how these iconic structures are formed. Finally, I will discuss part of my work here at the MPIA combining single-dish and interferometric data to link sites of high-mass star formation with their surroundings. Taken together, these projects reveal the value of striking our into new territory by exploring the space between our islands of knowledge.

2018-07-27
15:00
Reconstruction of the Milky Way with tidal streams
Ana Bonaca (CfA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
The arduous quest of reconstructing the distribution of matter in the Galaxy has been reinvigorated in the months following the second data release from the Gaia mission. Studies of cold stellar streams -- remnants of tidally disrupted globular clusters which trace the underlying gravitational potential -- received a particular boost thanks to the Gaia proper motions. Employing the Fisher information approach, we show that the mean track of a stream's 6D positions and velocities intrinsically constrains the total enclosed mass at the stream's current position. Furthermore, Gaia's view of the longest cold stream, GD-1, uncovered significant density variations along the stream and stars offset from the main track -- likely signatures of a perturbed past. Using multiple streams to measure the enclosed mass in different regions of the Milky Way, and GD-1 to test for the presence of low-mass dark matter subhalos, we should produce a 3D map of the Milky Way halo that can distinguish between competing cosmological models.

2018-07-27
15:00
Reconstruction of the Milky Way with tidal streams
Ana Bonaca (CfA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
The arduous quest of reconstructing the distribution of matter in the Galaxy has been reinvigorated in the months following the second data release from the Gaia mission. Studies of cold stellar streams -- remnants of tidally disrupted globular clusters which trace the underlying gravitational potential -- received a particular boost thanks to the Gaia proper motions. Employing the Fisher information approach, we show that the mean track of a stream's 6D positions and velocities intrinsically constrains the total enclosed mass at the stream's current position. Furthermore, Gaia's view of the longest cold stream, GD-1, uncovered significant density variations along the stream and stars offset from the main track -- likely signatures of a perturbed past. Using multiple streams to measure the enclosed mass in different regions of the Milky Way, and GD-1 to test for the presence of low-mass dark matter subhalos, we should produce a 3D map of the Milky Way halo that can distinguish between competing cosmological models.

2018-07-20
15:00
Science with the Stratospheric Observatory for Infrared Astronomy (Sofia)
Maja Kazmierczak-Barthel (DSI)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
The infrared is a key part of the electromagnetic spectrum for studying star formation and evolution, galaxies, planets, and the interstellar medium. As most infrared wavelengths are absorbed by the water vapor of our planet's atmosphere, except for a few narrow spectral windows, astronomical infrared observations have been limited to space-, balloon-, or aircraft-observatories. SOFIA is the last remaining observatory from a truly "Golden Age" for Mid- and Far-Infrared Astronomy, that included space missions like IRAS, ISO, Spitzer, and Herschel. At least for another decade or two SOFIA will be the only observatory that can regularly access the Mid-and Far-Infrared sky.

SOFIA consists of a 2.7m telescope (effective 2.5m), that is lifted by a heavily modified Boeing 747-SP into the stratosphere above more than 99% of the atmosphere's water vapor. A full complement of instruments provides imaging, spectroscopic, and polarimetric capabilities, to follow up and extend many discoveries of past infrared space missions that ended due to a limited supply of cryogen. In addition, it provides for more progress, as very new state of the art instrumentation can be used, returned to the lab, and further improved. The mobility of the facility gives rise to even more observational opportunities like stellar occultations and other targets of opportunity.

The presentation will give an overview over the capabilities of the observatory, including a few illustrative scientific applications. We will discuss the wavelength coverage, sensitivities, and observing modes, as well as limitations that arise from the specifics of an observational platform on-board of an aircraft. Particular emphasis will be given to the recently released "Cycle 7 Call for Proposals", the specific tools necessary for proposal generation, and how to successfully compete for observing time on SOFIA.

2018-07-20
15:00
Science with the Stratospheric Observatory for Infrared Astronomy (Sofia)
Maja Kazmierczak-Barthel (DSI)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
Show/hide abstract

Abstract
The infrared is a key part of the electromagnetic spectrum for studying star formation and evolution, galaxies, planets, and the interstellar medium. As most infrared wavelengths are absorbed by the water vapor of our planet's atmosphere, except for a few narrow spectral windows, astronomical infrared observations have been limited to space-, balloon-, or aircraft-observatories. SOFIA is the last remaining observatory from a truly "Golden Age" for Mid- and Far-Infrared Astronomy, that included space missions like IRAS, ISO, Spitzer, and Herschel. At least for another decade or two SOFIA will be the only observatory that can regularly access the Mid-and Far-Infrared sky.

SOFIA consists of a 2.7m telescope (effective 2.5m), that is lifted by a heavily modified Boeing 747-SP into the stratosphere above more than 99% of the atmosphere's water vapor. A full complement of instruments provides imaging, spectroscopic, and polarimetric capabilities, to follow up and extend many discoveries of past infrared space missions that ended due to a limited supply of cryogen. In addition, it provides for more progress, as very new state of the art instrumentation can be used, returned to the lab, and further improved. The mobility of the facility gives rise to even more observational opportunities like stellar occultations and other targets of opportunity.

The presentation will give an overview over the capabilities of the observatory, including a few illustrative scientific applications. We will discuss the wavelength coverage, sensitivities, and observing modes, as well as limitations that arise from the specifics of an observational platform on-board of an aircraft. Particular emphasis will be given to the recently released "Cycle 7 Call for Proposals", the specific tools necessary for proposal generation, and how to successfully compete for observing time on SOFIA.

2018-07-13
15:00
From VLT to ELT
Signature Speaker Michele Cirasuolo (ESO)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
In this presentation I will discuss three topics: some recent results obtained with KMOS on the physics and dynamics of high galaxies\; the current status of the MOONS instrument and the unprecedented capabilities of the new Extremely Large Telescope (ELT).

First I will discuss the latest results we have obtained from a Large Programme with KMOS called KLEVER. The programme is designed to observe and spatially resolve a sample of ~100 galaxies at 1<\;z<\;2.5 with full near-IR wavelength coverage (YJ,H,K) delivering the (nearly) full set of rest-frame optical nebular lines and therefore an extraordinary diagnostic power.

I will then present a scientific and technical overview of the MOONS instrument, a new multi-object spectrograph for the Very Large Telescope. The combination of high multiplex (1000 targets) and wide simultaneous wavelength coverage (0.64 - 1.8 microns) of MOONS will provide the astronomical community with a powerful, world-leading instrument able to serve a wide range of Galactic and Extragalactic studies.

Finally I will highlight the key science drivers of the new ESO's flagship facility: the Extremely Large Telescope.
The E-ELT is now under construction and with its 39-metre primary mirror it will be the largest optical/near-IR telescope in the world. I will present an overview of the E-ELT Programme, focusing on the latest status of the telescope, its instrumentation and the scientific synergies.

2018-07-13
15:00
From VLT to ELT
Signature Speaker Michele Cirasuolo (ESO)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
Show/hide abstract

Abstract
In this presentation I will discuss three topics: some recent results obtained with KMOS on the physics and dynamics of high galaxies\; the current status of the MOONS instrument and the unprecedented capabilities of the new Extremely Large Telescope (ELT).

First I will discuss the latest results we have obtained from a Large Programme with KMOS called KLEVER. The programme is designed to observe and spatially resolve a sample of ~100 galaxies at 1<\;z<\;2.5 with full near-IR wavelength coverage (YJ,H,K) delivering the (nearly) full set of rest-frame optical nebular lines and therefore an extraordinary diagnostic power.

I will then present a scientific and technical overview of the MOONS instrument, a new multi-object spectrograph for the Very Large Telescope. The combination of high multiplex (1000 targets) and wide simultaneous wavelength coverage (0.64 - 1.8 microns) of MOONS will provide the astronomical community with a powerful, world-leading instrument able to serve a wide range of Galactic and Extragalactic studies.

Finally I will highlight the key science drivers of the new ESO's flagship facility: the Extremely Large Telescope.
The E-ELT is now under construction and with its 39-metre primary mirror it will be the largest optical/near-IR telescope in the world. I will present an overview of the E-ELT Programme, focusing on the latest status of the telescope, its instrumentation and the scientific synergies.

2018-07-06
15:00
Gamma Rays from The Galactic Centre - an indirect sign for dark matter?
Johannes King (LSW)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
Gamma-ray astronomy is an established tool for studying the most energetic, non-thermal processes in the Universe. These processes are typically linked to the acceleration of cosmic rays, which in turn emit gamma-rays for example via inverse compton scattering or the decay of neutral pions. Another process that potentially yields a detecable gamma-ray signal is the annihilation or decay of dark matter particles. Since such a signal is proportional to the dark matter densitiy the Galactic Centre is the ideal place for indirect dark matter searches.

I will present recent studies of the gamma radiation from the Galactic Centre based on observations with H.E.S.S., an array of five imaging atmospheric Cherenkov telescopes located in Namibia. H.E.S.S. plays a major role in the indirect search for dark matter and will continue to do so in the coming years.

2018-07-06
15:00
Gamma Rays from The Galactic Centre - an indirect sign for dark matter?
Johannes King (LSW)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
Show/hide abstract

Abstract
Gamma-ray astronomy is an established tool for studying the most energetic, non-thermal processes in the Universe. These processes are typically linked to the acceleration of cosmic rays, which in turn emit gamma-rays for example via inverse compton scattering or the decay of neutral pions. Another process that potentially yields a detecable gamma-ray signal is the annihilation or decay of dark matter particles. Since such a signal is proportional to the dark matter densitiy the Galactic Centre is the ideal place for indirect dark matter searches.

I will present recent studies of the gamma radiation from the Galactic Centre based on observations with H.E.S.S., an array of five imaging atmospheric Cherenkov telescopes located in Namibia. H.E.S.S. plays a major role in the indirect search for dark matter and will continue to do so in the coming years.

2018-06-29
15:00
Stellar Forensics with the Most Powerful Explosions in the Universe
Maryam Modjaz (NYU)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
Supernovae (SNe) and Gamma-ray Bursts (GRBs) are exploding stars and constitute the most powerful explosions in the universe. Since they are visible over large cosmological distances, release almost all elements heavier than Helium, and leave behind extreme remnants such as black holes, they are fascinating objects, as well as crucial tools for many areas of astrophysics, including cosmology. However, for many years the fundamental question of which stellar systems give rise to which kinds of explosions has remained outstanding, for both Type Ia SNe used for cosmology as well as for Superluminous SNe and long-duration GRBs that must originate from special kinds of massive stars. I will discuss the exciting recent progress that we have made on this question in key areas by publishing and thoroughly analyzing the largest data sets in the world. I will conclude with an outlook on how the most promising venues of research - using the existing and upcoming innovative large time-domain surveys such as ZTF and LSST - will shed new light on the diverse deaths of stars.

2018-06-29
15:00
Stellar Forensics with the Most Powerful Explosions in the Universe
Maryam Modjaz (NYU)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
Show/hide abstract

Abstract
Supernovae (SNe) and Gamma-ray Bursts (GRBs) are exploding stars and constitute the most powerful explosions in the universe. Since they are visible over large cosmological distances, release almost all elements heavier than Helium, and leave behind extreme remnants such as black holes, they are fascinating objects, as well as crucial tools for many areas of astrophysics, including cosmology. However, for many years the fundamental question of which stellar systems give rise to which kinds of explosions has remained outstanding, for both Type Ia SNe used for cosmology as well as for Superluminous SNe and long-duration GRBs that must originate from special kinds of massive stars. I will discuss the exciting recent progress that we have made on this question in key areas by publishing and thoroughly analyzing the largest data sets in the world. I will conclude with an outlook on how the most promising venues of research - using the existing and upcoming innovative large time-domain surveys such as ZTF and LSST - will shed new light on the diverse deaths of stars.

2018-06-22
13:15
The production of dust in galaxies
Ciska Kemper (ASIAA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
The evolution of interstellar dust reservoirs, and the evolution of galaxies themselves go hand-in-hand, as the presence of dust alters evolutionary drivers, such as the interstellar radiation field and the star formation history, while at the same time, the dust is being formed and altered by processes taking place in galaxies. Indeed, dust can often even be used as a tracer of physical conditions. The exact mineralogical composition, the size and the shape of dust grains, are all affected by the physical conditions. Due to the more permanent nature of solids, dust grains provide a historical record of its processing history, while interstellar gas will only ever probe the
present conditions.

I will discuss our recent results on the Magellanic Clouds, Local Group galaxies, the Milky Way, AGN tori, and starburst galaxies, and highlight future observational opportunities open to astronomers to continue the study of interstellar dust in galaxies.

2018-06-22
13:15
The production of dust in galaxies
Ciska Kemper (ASIAA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
Show/hide abstract

Abstract
The evolution of interstellar dust reservoirs, and the evolution of galaxies themselves go hand-in-hand, as the presence of dust alters evolutionary drivers, such as the interstellar radiation field and the star formation history, while at the same time, the dust is being formed and altered by processes taking place in galaxies. Indeed, dust can often even be used as a tracer of physical conditions. The exact mineralogical composition, the size and the shape of dust grains, are all affected by the physical conditions. Due to the more permanent nature of solids, dust grains provide a historical record of its processing history, while interstellar gas will only ever probe the
present conditions.

I will discuss our recent results on the Magellanic Clouds, Local Group galaxies, the Milky Way, AGN tori, and starburst galaxies, and highlight future observational opportunities open to astronomers to continue the study of interstellar dust in galaxies.

2018-06-15
15:00
The chemical evolution of the Sculptor dwarf spheroidal galaxy (and what we can learn from it!)
Ása Skuladottir (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
At current date the Milky Way has over 50 known satellite galaxies, each
with unique properties. Sculptor is one of the classical dwarf spheroidal
galaxies, with a total mass on the order of ~3x10^8 Msun, and a relatively
high stellar mass for a Local Group dwarf galaxy system: ~8x10^6 Msun.
This galaxy is dominated by an old stellar population (>10 Gyr) and is
therefore an ideal system to study early chemical evolution. Currently we
have available detailed chemical abundances (up to 20 different elements)
for over 100 stars, covering the large metallicity range -4.0<[Fe/H]<-0.9,
(as well as less detailed abundances for ~400 stars), making this one of
the best chemically studied galaxy outside of the Milky Way. From the
details of Sculptor's chemical evolution history, we can therefore learn
valuable lessons about dwarf galaxies in general, as well as larger
systems.

2018-06-15
15:00
The chemical evolution of the Sculptor dwarf spheroidal galaxy (and what we can learn from it!)
Ása Skuladottir (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
Show/hide abstract

Abstract
At current date the Milky Way has over 50 known satellite galaxies, each
with unique properties. Sculptor is one of the classical dwarf spheroidal
galaxies, with a total mass on the order of ~3x10^8 Msun, and a relatively
high stellar mass for a Local Group dwarf galaxy system: ~8x10^6 Msun.
This galaxy is dominated by an old stellar population (>10 Gyr) and is
therefore an ideal system to study early chemical evolution. Currently we
have available detailed chemical abundances (up to 20 different elements)
for over 100 stars, covering the large metallicity range -4.0<[Fe/H]<-0.9,
(as well as less detailed abundances for ~400 stars), making this one of
the best chemically studied galaxy outside of the Milky Way. From the
details of Sculptor's chemical evolution history, we can therefore learn
valuable lessons about dwarf galaxies in general, as well as larger
systems.

2018-06-08
15:00
Asteroseismology in the Gaia Era
Marc Pinsonneault (OSU)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
Stellar oscillations are powerful tools for understanding the structure and evolution of stars. With the advent of time domain space missions they can now be measured for large samples of evolved cool stars. The combination of this asteroseismic data, astrometry from Gaia, and large spectroscopic surveys is transforming our understanding of stellar populations and stellar physics. In this talk I review the current state of the art in red giant asteroseismology: both how well we can measure stellar properties using it and how it has changed our understanding of stellar populations. I will also discuss the powerful combination of asteroseismology and

2018-06-08
15:00
Asteroseismology in the Gaia Era
Marc Pinsonneault (OSU)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
Stellar oscillations are powerful tools for understanding the structure and evolution of stars. With the advent of time domain space missions they can now be measured for large samples of evolved cool stars. The combination of this asteroseismic data, astrometry from Gaia, and large spectroscopic surveys is transforming our understanding of stellar populations and stellar physics. In this talk I review the current state of the art in red giant asteroseismology: both how well we can measure stellar properties using it and how it has changed our understanding of stellar populations. I will also discuss the powerful combination of asteroseismology and

2018-06-01
15:00
The Lowest-Mass Galaxies in the Early Universe: Insights from the Local Group
Dan Weisz (UC Berkeley)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
The Local Group is home to ~100 galaxies less massive than the Small Magellanic Cloud (10^8 Msun). Such low-mass galaxies have become increasingly relevant to a broad range of astrophysics from cosmic reionization to deciphering the nature of dark matter. Yet, they are simply too faint to be directly detected at any appreciable redshift, compromising our ability to place them into a cosmological context. In this talk, I will describe how observations of resolved stellar populations in Local Group galaxies enable the measurement of detailed star formation histories, which provide the only avenue for tracing the evolution of low-mass galaxies across cosmic time. I will review our current knowledge of low-mass galaxy evolution over 6 decades in stellar mass, with a particular emphasis on the early Universe. I will illustrate how local observations of stars and galaxies can be used in tandem with high-redshift studies to improve our understanding of cosmic reionization. I will conclude by discussing prospects for increased synergy between near-field and far-field galaxy studies in the JWST era.

2018-06-01
15:00
The Lowest-Mass Galaxies in the Early Universe: Insights from the Local Group
Dan Weisz (UC Berkeley)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
The Local Group is home to ~100 galaxies less massive than the Small Magellanic Cloud (10^8 Msun). Such low-mass galaxies have become increasingly relevant to a broad range of astrophysics from cosmic reionization to deciphering the nature of dark matter. Yet, they are simply too faint to be directly detected at any appreciable redshift, compromising our ability to place them into a cosmological context. In this talk, I will describe how observations of resolved stellar populations in Local Group galaxies enable the measurement of detailed star formation histories, which provide the only avenue for tracing the evolution of low-mass galaxies across cosmic time. I will review our current knowledge of low-mass galaxy evolution over 6 decades in stellar mass, with a particular emphasis on the early Universe. I will illustrate how local observations of stars and galaxies can be used in tandem with high-redshift studies to improve our understanding of cosmic reionization. I will conclude by discussing prospects for increased synergy between near-field and far-field galaxy studies in the JWST era.

2018-05-18
15:00
detecting optimal targets for characterization & understanding
Nestor Espinoza (MPIA) : Transiting exoplanets
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
Transiting exoplanets are exciting objects to study because, with sufficient follow-up, they can be almost completely characterized. From bulk and atmospheric compositions to a plethora of orbital information, these exoplanets can provide key information that, in principle, enable us to build (and test) models to understand how they are shaped to their present-day forms. However, only a handful of transiting exoplanets "optimal" for characterization exist, despite the large number of confirmed transiting exoplanets detected to date\; their detection and characterization is thus an important challenge on its own. In this talk, I will present our on-going efforts with the K2-CL collaboration to find new, interesting characterizable systems with the K2 mission, how and why these have to be followed up after their discovery to keep their ephemerides up to date, and our efforts within the ACCESS survey, with which we are exploring exoplanet atmospheres of interesting targets in the optical window, which is key to unveil what their atmospheres are made of, specially if combined with HST/WFC3 data. Lessons learned and natural transitions of these projects in light of the upcoming TESS and JWST missions will be discussed.

2018-05-18
15:00
detecting optimal targets for characterization & understanding
Nestor Espinoza (MPIA) : Transiting exoplanets
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
Show/hide abstract

Abstract
Transiting exoplanets are exciting objects to study because, with sufficient follow-up, they can be almost completely characterized. From bulk and atmospheric compositions to a plethora of orbital information, these exoplanets can provide key information that, in principle, enable us to build (and test) models to understand how they are shaped to their present-day forms. However, only a handful of transiting exoplanets "optimal" for characterization exist, despite the large number of confirmed transiting exoplanets detected to date\; their detection and characterization is thus an important challenge on its own. In this talk, I will present our on-going efforts with the K2-CL collaboration to find new, interesting characterizable systems with the K2 mission, how and why these have to be followed up after their discovery to keep their ephemerides up to date, and our efforts within the ACCESS survey, with which we are exploring exoplanet atmospheres of interesting targets in the optical window, which is key to unveil what their atmospheres are made of, specially if combined with HST/WFC3 data. Lessons learned and natural transitions of these projects in light of the upcoming TESS and JWST missions will be discussed.

2018-05-11
15:00
Exploring the Evolution of Circumstellar Disks with ALMA
John Carpenter (Joint ALMA Observatory)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
ALMA is providing new opportunities to explore the evolution of circumstellar disks. From snapshot surveys of protoplanetary disks in nearby star forming regions, to sensitive high-resolution images of young disks, and to surveys of old debris disks, ALMA is tracing the structure and properties of disks at all evolutionary stages. This talk will present recent ALMA observations that are contributing to our understanding of the properties of protoplanetary and debris disks. I will first summarize the results from recent ALMA surveys that are establishing the demographics of protoplanetary disks between ages of 1 and 10 Myr. I will also present new high-resolution images of 20 protoplanetary disks from an ALMA Large Program that is designed to determine the prevalence of substructure (e.g., rings, spirals, and gaps) in young protoplanetary disks. Finally, I will present new ALMA data for a debris disk around a ~ 100 Myr old solar analog and discuss the implications for planet formation in this system.

2018-05-11
15:00
Exploring the Evolution of Circumstellar Disks with ALMA
John Carpenter (Joint ALMA Observatory)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
ALMA is providing new opportunities to explore the evolution of circumstellar disks. From snapshot surveys of protoplanetary disks in nearby star forming regions, to sensitive high-resolution images of young disks, and to surveys of old debris disks, ALMA is tracing the structure and properties of disks at all evolutionary stages. This talk will present recent ALMA observations that are contributing to our understanding of the properties of protoplanetary and debris disks. I will first summarize the results from recent ALMA surveys that are establishing the demographics of protoplanetary disks between ages of 1 and 10 Myr. I will also present new high-resolution images of 20 protoplanetary disks from an ALMA Large Program that is designed to determine the prevalence of substructure (e.g., rings, spirals, and gaps) in young protoplanetary disks. Finally, I will present new ALMA data for a debris disk around a ~ 100 Myr old solar analog and discuss the implications for planet formation in this system.

2018-05-04
15:00
Jupiter's Jet-Streams and interior revealed by Juno
Yamila Miguel (Leiden)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract

Giant planets were the first planets to form and the most influential ones. Their interiors and atmospheres have crucial information to understand the origins of the solar system and of our own Earth.  \;

With the aim to reach a deeper understanding of Jupiter's interior and atmosphere, the Juno spacecraft was sent to the biggest giant in the solar system, and its first results have fundamentally changed our understanding of this planet. \;


In this seminar I will show the models we use to understand Jupiter's interior and our latest Juno results -including a much deeper understanding of Jupiter's interior and jet streams-, that will help us to reach a better understanding of Jupiter formation history.


2018-05-04
15:00
Jupiter's Jet-Streams and interior revealed by Juno
Yamila Miguel (Leiden)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract

Giant planets were the first planets to form and the most influential ones. Their interiors and atmospheres have crucial information to understand the origins of the solar system and of our own Earth.  \;

With the aim to reach a deeper understanding of Jupiter's interior and atmosphere, the Juno spacecraft was sent to the biggest giant in the solar system, and its first results have fundamentally changed our understanding of this planet. \;


In this seminar I will show the models we use to understand Jupiter's interior and our latest Juno results -including a much deeper understanding of Jupiter's interior and jet streams-, that will help us to reach a better understanding of Jupiter formation history.


2018-04-27
15:00
Neutron star mergers and the high-density equation of state
Andreas Bauswein (HITS)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
In August 2017 the LIGO-Virgo network detected for the first time gravitational waves from a neutron star merger. The event, dubbed GW170817, was followed by electromagnetic radiation. Various emission mechanisms produced radiation at different wavelengths throughout the electromagnetic spectrum from gamma rays to radio. The gravitational and electromagnetic radiation has provided a wealth of information on the physics of neutron star mergers. In particular, it was possible to infer constraints on stellar properties of neutron stars and the only incompletely known equation of state of high-density matter. Specifically, bounds on neutron star radii have been derived from this very first observation of a neutron star merger. Future detections with increased sensitivity promise accurate and robust measurements of neutron star properties and thus to elucidate properties of high-density matter.

2018-04-27
15:00
Neutron star mergers and the high-density equation of state
Andreas Bauswein (HITS)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
In August 2017 the LIGO-Virgo network detected for the first time gravitational waves from a neutron star merger. The event, dubbed GW170817, was followed by electromagnetic radiation. Various emission mechanisms produced radiation at different wavelengths throughout the electromagnetic spectrum from gamma rays to radio. The gravitational and electromagnetic radiation has provided a wealth of information on the physics of neutron star mergers. In particular, it was possible to infer constraints on stellar properties of neutron stars and the only incompletely known equation of state of high-density matter. Specifically, bounds on neutron star radii have been derived from this very first observation of a neutron star merger. Future detections with increased sensitivity promise accurate and robust measurements of neutron star properties and thus to elucidate properties of high-density matter.

2018-04-20
15:00
10 years of Galaxy Evolution
Arjen van der Wel (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
To conclude my ~10-year stay at MPIA I will give an overview of the progress in understanding the formation and evolution of galaxies that we have made over the past decade. This summary will be broad, ranging from theory and simulations to the observations of distant star-bursting dwarf galaxies, but from the specific perspective provided by large optical/near-IR surveys. I will describe how MPIA has stood at the forefront of the transition from an era of discovery -- which showed where the stars in the universe are and when they formed --  \;to an era of concrete physical insight in to the galaxy evolution process.

2018-04-20
15:00
10 years of Galaxy Evolution
Arjen van der Wel (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
To conclude my ~10-year stay at MPIA I will give an overview of the progress in understanding the formation and evolution of galaxies that we have made over the past decade. This summary will be broad, ranging from theory and simulations to the observations of distant star-bursting dwarf galaxies, but from the specific perspective provided by large optical/near-IR surveys. I will describe how MPIA has stood at the forefront of the transition from an era of discovery -- which showed where the stars in the universe are and when they formed --  \;to an era of concrete physical insight in to the galaxy evolution process.

2018-04-13
15:00
High-resolution cosmological simulations of Milky Way mass galaxies"
Tobias Buck (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
The Milky Way and its dwarf galaxy companions are among the most well studied galaxy we know.
Current very high-resolution zoom-in baryonic simulations of the formation of Milky Way mass galaxies are in incredible
agreement with observed properties our Milky Way. First, I will introduce the new high-resolution set of simulations from the NIHAO project and discuss the formation of the Milky Way. I will cover the early phases of violent star formation and the accretion of its satellites providing observational constraints on the effect of environment dwarf galaxy properties. I will further discuss the (kinematic) structure and evolution of the stellar disc and the morphology and abundance patterns of the Milky Way's central region - its bar and boxy/peanut bulge. Using these simulations I am able to provide a theoretical understanding of the formation of the Milky Way in the era of Gaia.

2018-04-13
15:00
High-resolution cosmological simulations of Milky Way mass galaxies"
Tobias Buck (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
The Milky Way and its dwarf galaxy companions are among the most well studied galaxy we know.
Current very high-resolution zoom-in baryonic simulations of the formation of Milky Way mass galaxies are in incredible
agreement with observed properties our Milky Way. First, I will introduce the new high-resolution set of simulations from the NIHAO project and discuss the formation of the Milky Way. I will cover the early phases of violent star formation and the accretion of its satellites providing observational constraints on the effect of environment dwarf galaxy properties. I will further discuss the (kinematic) structure and evolution of the stellar disc and the morphology and abundance patterns of the Milky Way's central region - its bar and boxy/peanut bulge. Using these simulations I am able to provide a theoretical understanding of the formation of the Milky Way in the era of Gaia.

2018-04-06
15:00
The second Gaia data release
Coryn Bailer-Jones (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract

On 25 April the Gaia Consortium will make its second data release based
on 22 months of mission data. The release will contain five-parameter
astrometry and three-band photometry for over 1 billion stars down to
G=20.7, radial velocities for 7 million stars, variability
classification for several hundred thousand stars, plus basic stellar
parameters for up to 160 million stars. I will give an overview of the
content, precision, and coverage of this release plus some tips on how
(not) to use the data.

2018-04-06
15:00
The second Gaia data release
Coryn Bailer-Jones (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
Show/hide abstract

Abstract

On 25 April the Gaia Consortium will make its second data release based
on 22 months of mission data. The release will contain five-parameter
astrometry and three-band photometry for over 1 billion stars down to
G=20.7, radial velocities for 7 million stars, variability
classification for several hundred thousand stars, plus basic stellar
parameters for up to 160 million stars. I will give an overview of the
content, precision, and coverage of this release plus some tips on how
(not) to use the data.

2018-03-23
15:00
The Role of Environment in Shaping Molecular Cloud Structure and Star Formation
Chris Faesi (MPIA)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
Giant Molecular Clouds (GMCs) are the cradles of stellar birth across the universe and thus play a key role in the baryon cycle within galaxies. GMCs in the Milky Way show a high degree of uniformity in their physical structure, but recent observations of nearby galaxies have suggested that their properties may vary systematically with environment. To explore the question of universality vs. environment, I have undertaken a series of high-resolution, high-sensitivity studies of molecular gas and star formation in NGC 300, a low mass, star forming spiral galaxy that at a distance of 2 Mpc provides an ideal laboratory for resolved GMC studies and comparison to our own Galaxy. I will describe the results of a campaign of multiwavelength observations of NGC 300 culminating in an ALMA study that achieves 10 pc resolution, fully resolving GMC scales in a sample of 250 clouds. I will show that despite large differences between global properties of the Milky Way and NGC 300, their GMC populations appear to be remarkably similar. Furthermore, the relationship between star formation and molecular gas identified in the Milky Way also holds in NGC 300. I will demonstrate that local physical properties such as midplane disk pressure of the interstellar medium, which is similar between the Milky Way and NGC 300, may explain observed differences in GMC properties in other galaxies such as M51, as well as in more extreme physical environments such as the Galactic Center. I will conclude by describing the ongoing campaign to link small-scale interstellar medium physics with large-scale galaxy properties under the auspices of the PHANGS (Physics at High Angular resolution in Nearby GalaxieS) collaboration. We have in-progress large programs with both ALMA and MUSE to measure molecular gas and tracers of star formation at arcsecond resolution across the disks of tens of galaxies, providing improved statistics and greatly expanding the parameter space for GMC-scale analyses in a range of environments.

2018-03-16
15:00
Crowded field 3D spectroscopy in NGC300 - spectacular details of resolved stellar populations revealed through the combination of ACS with MUSE
Martin Roth (AIP)
Königstuhl Kolloquium
Max-Planck-Institut für Astronomie, Level 3 Lecture Hall (301)
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Abstract
Already a decade ago, the Advanced Camera for Surveys Nearby Galaxy survey Treasury (ANGST) has provided images and photometry of individual stars in nearby galaxies, thus furnishing the hope to provide deep insight into star formation histories and the chemical evolution of galaxies. However, the known limitations of photometry have remained an obstacle to fully exploit the angular resolution of HST in analyzing stellar populations in galaxies such as the sculptor group galaxy NGC300. We have selected NGC300 as the target of our MUSE GTO program at the VLT UT4 to explore the potential of IFUs for crowded field 3D spectroscopy, utilizing PSF-fitting techniques that have become a standard for imaging data in the optical and NIR already for some time (DAOPHOT etc.). With the input of stellar centroids obtained from the ANGST catalogue, we are demonstrating that the PampelMuse PSF-fitting tool is capable to extract more than 500 spectra for individual stars of luminosity class I?III from a single MUSE pointing (1.5 h exposure time). These spectra are well deblended and allow for spectral type classification as well as the measurement of radial velocities. Next to stars of spectral types O?M, we find numerous carbon stars, blue emission line stars, and LBV and symbiotic star candidates. The excellent image quality and sensitivity of MUSE has also enabled the discovery of extremely faint HII regions, planetary nebulae, supernova remnants, and substructure of the diffuse ionized gas (DIG).

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