Ruprecht-Karls-Universität Heidelberg

Heidelberg Joint Astronomical Colloquium


Upcoming events


2018-12-18
16:15
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Star formation from kpc to hundreds of AU scales
Henrik Beuther (MPI for Astronomy (Heidelberg))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, Großer Hörsaal
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Abstract
Star formation is a hierarchical process where fragmentation and gas dynamical processes start on the largest galactic scales and continue down to the formation and accretion processes around the protostars. Starting with bar-spiral arm interfaces, then going step-wise to smaller scales of molecular clouds, star-forming regions, cores and potential (massive)accretion disks, I will present recent observational results related to the dynamical processes during cloud and star formation.

2019-01-08
16:15
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The IllustrisTNG Project
Lars Hernquist (Harvard-Smithsonian Center for Astrophysics, Cambridge (USA))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, Großer Hörsaal

2019-01-15
16:15
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How can nucleosynthesis constrain explosions? New perspectives using multi-D supernova models
Claudia Travaglio (INAF (Turino))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, Großer Hörsaal
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Abstract
During this seminar I will describe my research program aiming at a better understanding of the physics of supernovae and of the origin of nuclei by increasing the quality and predictive power of numerical models as well as nucleosynthesis calculations. Supernovae play essential roles in the frameworks of many branches of astrophysics: star formation, galaxy dynamics, high-energy astrophysics, galactic chemical evolution, and cosmology. In spite of their ubiquitous presence in astrophysics, there are many uncertainties related to progenitor systems, treatment of the explosions, cross section determinations at such high temperatures, and comparisons with spectra. Most popular results in the field of nucleosynthesis during explosions are still mostly based on one-spatial dimension calculations. The pioneering and very innovative aspect today is the possibility of coupling nucleosynthesis to multidimensional simulations of different type of supernovae. I will show recent results and future perspectives in multi-dimensional calculations of thermonuclear as well as core-collapse supernovae, using tracer particle method for nucleosynthesis. I will illustrate detailed comparison of 1D and 3D supernova models with nucleosynthesis calculations and discussing the needs of multi-D (and where it is needed). Despite the huge investments in nuclear physics experiments, theoretical studies establishing priority lists of reactions to be measured and precision required for astrophysics are currently very limited. During this seminar I will also discuss a priority list for future experiments and improvements in predictions of key nuclear reactions for explosive nucleosynthesis. My expertise in Galactic Chemical Evolution modelling lead to the possibility to study a dependence of the SNe yields on metallicity and their contribution over the galactic age up to reproducing the Solar System composition. During my talk I will refer different times to result of chemical evolution studies with the need of a more clear understanding of the impact of supernovae at the earliest stages of the evolution of galaxies, and their contribution to the Solar System composition. The wealth of information from galactic surveys makes this the ideal time for a theorist to understand the formation and evolution of galaxies with a new generation of chemical evolution models. To this goal, at the end of my talk, I will describe a novel project to model chemo-dynamical evolution of the cosmos, based on a N-body SPH RAMSES code making use of the framework on a moving mesh, adjusting automatically spatial resolution but using a large number of isotopes.

2019-01-22
16:15
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Hunting ghostly galaxies with the Dragonfly Telephoto Array
Pieter van Dokkum (Yale University)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, Großer Hörsaal

2019-01-29
16:15
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Formation and properties of galactic discs: The N-body view
Lia Athanassoula (Laboratoire d’Astrophysique de Marseille (France))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, Großer Hörsaal

2019-02-05
16:15
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Molecular tori, black hole fueling and feedback in nearby AGN
Francoise Combes (Observatoire de Paris (France))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, Großer Hörsaal


Past events


2018-12-11
16:15
Carbon-enhanced metal-poor stars: probes of first-star nucleosynthesis and galaxy assembly
Timothy C. Beers (University of Notre Dame (USA))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, Großer Hörsaal
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Abstract
Over the course of the past few decades, it has become clear that the class of metal-poor stars known as carbon-enhanced metal-poor (CEMP) stars are powerful probes of a number of areas of interest to contemporary astrophysics. I review the multiple lines of evidence that demonstrate the association of CEMP-no stars (which do not exhibit neutron-capture element enhancements) with the nucleosynthesis products of the very first stars, their likely birth place in low-mass mini-halos, and (once accreted by the halo) their role as tracers of the outer-halo population of the Galaxy. The CEMP-s stars (which exhibit enhancements of the heavy s-process elements), by contrast, are likely to have been born in more massive mini-halos, and serve as tracers of the inner-halo population. The well-known increasing frequency of CEMP-no stars (and newly recognized relative constancy of CEMP-s stars) with declining metallicity, and the identification of the primary groups in the Yoon-Beers diagram of A(C) vs. [Fe/H], provide the means to explore these associations in more detail, and to constrain numerical models of the formation of the Milky Way.

2018-12-04
16:15
Evaluating Cosmic Dawn
Anastasia Fialkov (Institute of Astronomy, Cambridge (UK))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, Großer Hörsaal
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Abstract
Cosmic dawn is one of the least-explored epochs in the history of the Universe illuminated by the very first stars and black holes. 21-cm radio signal produced by the intergalactic neutral hydrogen is tied to the intensity of radiation generated by these first sources of light. The signal can be used to constrain process of primordial star and black hole formation as well as reionization. In my talk I will discuss astrophysical processes that drive the signal. Pioneering radio experiments such as EDGES High-Band and SARASII deliver data which are capable to disfavor large sections of the high-redshift astrophysical parameter space. I will show the first observational constraints on reionization and cosmic dawn derived using the data of global 21-cm experiments at redshifts z~6-14. I will also discuss combined constraints with high-redshift quasars and Lyman Break Galaxies. Finally, I will comment on the claimed detection made with the EDGES Low-Band antenna at z~17.

2018-11-27
16:15
Asteroid Vesta and Jupiter's formation: an astrochemical tale
Diego Turrini (INAF-IAPS Rom, Italy)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, Großer Hörsaal
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Abstract
The first few millions of years of the life of the Solar System, when the young Sun was surrounded by its protoplanetary disk, is a period extremely difficult to investigate and of which we still know very little. Advancements in theoretical models of planetary formation have highlighted the existence of different paths for the formation of the first generations of solid bodies, starting from different formation environments and resulting in different final properties. In parallel, they also highlighted how the formation of giant planets and their orbital migration played a major role in determining how violent the dynamical and collisional evolution of the young Solar System was. As a result, not only the number of proposed formation scenarios has dramatically increased, but even formation scenarios based on extremely different evolutionary paths appear capable of producing final outcomes quite similar to the current Solar System. Luckily for us asteroid Vesta, one of the two targets of the NASA mission Dawn, offers the key to solve this conundrum. Dawn confirmed Vesta's volcanic crust as the source of a specific family of meteorites, the Howardite-Eucrite-Diogenite meteorites (also known collectively as HEDs) and this 'genetic' link reveals that Vesta is one of the most ancient bodies in the Solar System and witnessed the appearance of its giant planets. Together, the HEDs and Dawn tell us two important facts about Vesta. The first one is that the impacts it experienced over the whole life of the Solar System could not destroy its volcanic crust and expose the underlying mantle. The second one is that the early impacts that occurred when the young crust was still partially molten delivered only limited amounts of exogenous materials, most importantly water and metals, to it. Using the formation of Jupiter as a case study, in this talk I'll show how the joint use of these two pieces of information provides a new astrochemical constraint against which to test and quantitatively compare the different scenarios for the formation of the Solar System and the evolution of its protoplanetary disk. Finally, I'll show how the hindsight gained through the study of the Solar System can be applied to investigating circumstellar disks hosting young giant planets around other stars.

2018-11-20
16:15
What sets the stellar initial mass function? Why is it so universal?
Patrick Hennebelle (CEA Saclay (France))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, Großer Hörsaal
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Abstract
Stars are building blocks of our Universe. They determine its chemical evolution through nuclear synthesis, they host planets and they determine the evolution of galaxies. The characteristics of stars is predominantly determined by their masses. As such the stellar mass spectrum, also called the initial mass function (IMF), is truly a fundamental quantity to understand how our Universe works. A large number of studies have been performed to infer the IMF and it appears strikingly universal. That is to say, even when measured in rather different environments, the IMF presents no or modest variations. This is an intriguing fact as naive expectations would naturally relate the mass spectrum of stars to quantities such as the Jeans mass which depends significantly on the gas density and gas temperature. During the talk I will review some of the ideas that have been proposed to explain the IMF and discuss their success and failure. I will then present a large sets of simulations in which the initial conditions, the thermodynamics and the numerical resolution are all systematically varied. These simulations reveal that the initial conditions determine the power-law part of the IMF while the gas effective equation of state (EOS), which describe the isothermal to adiabatic transition, sets the peak of the stellar distribution. Analytical models are developed and compared with the simulation results. It is argued that the power-law part of the mass spectrum is due to an interplay between gravity and turbulence that determine the mass spectrum of gas reservoirs from which stars built their masses. The peak on the other hand, occurs at a mass which is 5-10 times the mass of the first Larson hydrostatic cores determined by the effective EOS. We propose that the very reason of the IMF weak variability is that the first hydrostatic core and immediate surrounding collapsing envelope are small scale processes which are nearly independent of the large scale environment characteristics. I will finish the talk by discussing remaining issues and suggests a possible "unifying picture".

2018-11-13
16:15
The growth of spiral galaxies over cosmic time
Richard Tuffs (MPI for Nuclear Physics (Heidelberg))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, Großer Hörsaal
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Abstract
A growing body of photometric, imaging and spectroscopic measurements of the distant galaxy population over the last decade have led to a concensus that the stars that we see today in the local Universe predominantly formed over the past 10Gyr in rotationally-supported and secularly evolving disk-dominated galaxies. Although this observational picture of the evolution of star formation with cosmic time is now well established, observational constraints on how the growth of galaxian disks is modulated (with respect to the overall evolution of the density of the Universe) by the non-linear growth of the parent dark matter (DM) haloes of galaxies have hitherto been limited to indirect statistical treatments, which moreover have been agnostic to galaxy morphology. After an introductory review, I will present results obtained using the Galaxy And Mass Assembly (GAMA) spectroscopic survey, of the so-called "Main Sequence" (MS) relation between SFR and stellar mass for morphologically-selected disk-dominated galaxies in the local Universe. These results are used to examine how the MS relation depends (at fixed stellar mass) on the mass of the host DM halo, as measured through kinematic and weak lensing data. I will also examine the dependence of the relation on cosmic time over the past Gyr - from which the present-day time-derivative of the light curve of galaxy disks in the UV as a function of their stellar mass will be inferred - and the effect on the MS relation and its scatter of whether a galaxy is a dominant central galaxy or is a satellite orbiting within the halo. The overall picture given by this analysis is one in which the efficiency of the condensation of baryons in the intergalactic medium into stars in galaxy disks as a function of halo mass varies according to a simple time-independent power law relation. Overall, this picture suggests that the present day diversity of the galaxy population, in particular the well-known propensity of red/blue galaxies to inhabit more/less dense regions of the cosmic web, and the rapidity at which the star formation activity of the Universe is being extinguished, is driven mainly by the transformation of morphology from disks to spheroids in different environments, rather than by variations of the cooling and accretion of the intergalactic medium onto galaxies as a function of environment.

2018-11-06
16:15
The role of chemistry in the formation of stars
Simon Glover (Center for Astronomy (Heidelberg))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, Großer Hörsaal
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Abstract
The good correlation that is observed in local spiral galaxies between the molecular gas surface density and the star formation rate surface density demonstrates that there is a close connection between the presence of molecular gas and the formation of stars. However, the nature of this connection remains a matter of some debate. Does efficient star formation require the cooling provided by carbon monoxide (CO) and other heavy molecules? Or are they simply good tracers of conditions conducive to star formation? In this talk, I will discuss the role that molecules such as CO play in governing the thermal balance of interstellar gas and present the results of some recent simulations designed to explore the connection between molecular gas and star formation.

2018-10-30
16:15
H0 and the never-ending story of the expansion rate of the universe
Bruno Leibundgut (ESO Garching (Germany))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, Großer Hörsaal
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Abstract
The uncertainty of the measured Hubble constant (H0) has been reduced by more than a factor of 10 over the past three decades. Despite this significant improvement the discussion on H0 continues unabated. The value of the Hubble constant sets the size and age of the universe. Since H0 is based on an absolute measurement, it is regarded as the most difficult cosmological parameter to determine. In particular, a discrepancy between local determinations of H0 and the ones based on cosmological models has emerged. It has been speculated that if the tension is confirmed an additional cosmological parameter would have to be introduced. The critical measurements of the distance ladder and in particular the use of supernovae as distance indicators will be discussed within this context.

2018-10-23
16:14
The photoevaporation of protoplanetary discs
Cathie J. Clarke (Cambridge, UK)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, Großer Hörsaal
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Abstract
Planets form in dusty discs whose upper layers are bathed in energetic radiation, either deriving from the central star or from massive stars in the local environment. Heating of surface layers can drive powerful winds which can limit the lifetime of discs and their planet forming potential. I will describe some highlights of recent research into disc photoevaporation, emphasising in particular the evidence for substantial photoevaporative losses from environmental heating even in rather sparse birth environments. I will also show how recent studies in OB associations demonstrate that proximity to neighouring OB stars has a significant impact on disc lifetimes and can be used to test theories of disc photoevaporation.

2018-07-24
16:15
Models of galaxy formation and evolutions: recent progress and open questions - the view from the GAlaxy Evolution and Assembly (GAEA) model.
Gabriella de Lucia
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
Understanding the physical mechanisms driving the formation and evolution of galaxies in a cosmological context represents one of the most important yet unresolved questions of modern astrophysics. Different methods have been developed over the years to link the physical properties of galaxies to the dark matter haloes in which they reside. I will give a brief overview of the aims and limits of these methods, with particular emphasis on semi-analytic models of galaxy formation. I will then review recent developments of our model for GAlaxy Evolution and Assembly (GAEA), and discuss the role of various physical processes in shaping the measured evolution of the galaxy stellar mass function and mass metallicity relation. I will overview our recent work to include a treatment for the partition of cold gas in its atomic and molecular gas components, and a variable stellar Initial Mass Function. I will conclude by discussing open problems and future perspectives.

2018-07-17
16:15
Protoplanetary disks at high angular resolution
Cornelis P. Dullemond (Institut für theoretische Astrophysik, Heidelberg)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
With ALMA and high-contrast optical/IR imaging, protoplanetary disks are revealed to be structured objects. They display rings, spirals, vortices and warps. These structures appear to be extremely well-defined and often have high contrast. This poses the question: what processes cause these conspicuous structures? Are these signs of planet formation? Or do they betray the existence of just-born planets in these disks? In this talk I will discuss these observations and some theoretical models that attempt to explain them. I will show that these structures indicate that dust “pebbles” are being moved around and are trapped in so-called “pressure traps”. I will show that planetary/substellar companions perturb the disk, but that also disk-internal processes can explain some of the ringlike dust traps. Finally I will discuss some ideas to explain the strong warps seen in some of these protoplanetary disks.

2018-07-10
16:15
From the Galaxy to clumps and back again: a tale of star formation from Galactic plane surveys
Sergio Molinari (Inst. Natl. Astrophys., Rome, Italy)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
The Milky Way Galaxy, our home, is a complex ecosystem where a cyclical transformation process brings diffuse barionic matter into dense unstable condensations to form stars, that produce radiant energy for billions of years before releasing chemically enriched material back into the ISM in their final stages of evolution. Star formation is the trigger of this process, eventually driving the evolution of ordinary matter in the Universe from its primordial composition to the present-day chemical diversity necessary for the birth of life. I will present an overview of the Milky Way Galaxy as a star formation engine as painted by the last generation Galactic Plane surveys in continuum and molecular lines. Pivoting around the Herschel Hi-GAL far infrared and submillimeter survey, the multiwavelength Milky Way now offers a complete and statistically significant observational scenario from diffuse ISM clouds, through the pervasive network of filamentary structures, down to the formation of dense clumps and embedded stellar clusters from the individual star formation site to the panoramic view of entire spiral arms. With the VIALACTEA project we organised and analysed these datasets in a unified framework, deploying a homogeneous analysis and classification scheme for nearly 30,000 candidate filamentary structures and more than 100,000 dense clumps with heliocentric distance determinations. We are now able to complete the first resolved map of the Star Formation Rate in the Milky Way and analyse in detail its variation with Galactocentric distance and with respect to spiral arms, as well as in comparison to star formation triggering agents.

2018-07-03
16:15
Galaxy Formation and Evolution in 3D
Lisa Kewley (Australian National Univ.)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
Tracing matter and chemical elements in the Universe is critical for understanding the formation of the first galaxies, the formation and growth of supermassive black holes, and ultimately the evolution of galaxies like our Milky Way. Throughout the history of the universe, large-scale gas flows have moulded the arms of spiral galaxies, formed the bulges of the most massive galaxies in the universe, fed supermassive black holes in the centers of galaxies, fueled generation upon generation of new stars, and enriched the intergalactic medium with metals. The physics and impact of these processes can now be traced through new efficient, wide-field 3D integral field spectrographs. We use multi-object integral field spectroscopy to build the largest local sample of galaxies with wide 3-dimensional imaging spectroscopy. We combine our local results with insights into the early universe probed through gravitational lensing and adaptive optics. I will present the latest results from our large local and high-z 3D surveys to understand the relationship between gas inflows, galactic-scale outflows, star-formation, chemical enrichment, and active galactic nuclei in galaxies. I will finish by discussing how this field will be transformed in the JWST and ELT era.

2018-06-26
16:15
Pulsar Winds
John Kirk (Max Planck Institut für Kernphysik, Heidelberg)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
Pulsar Winds and the nebulae which they energize (PWN) are among the most enigmatic objects in astrophysics. They consist of a relativistic, magnetized, electron-positron plasma that forms a compact cloud surrounding young pulsars. Their nonthermal synchrotron and inverse-Compton emission is detected from the radio band to very high energy (TeV) gamma-rays, where they are the dominant galactic source population. The radio-to-infrared spectra of PWN are flat, indicating a remarkably efficient particle acceleration mechanism, able to transfer most of the system energy into a tiny fraction of particles. Despite decades of research, the mechanism responsible for accelerating these particles has remained elusive, and poses one of the greatest challenges in particle acceleration theory. In this talk I will give an introduction to the physics of pulsar winds, and describe recent work on the acceleration mechanisms thought to be at work. These include not only variants of the well-known first-order Fermi mechanism, but also "inductive acceleration", which may explain the mysterious gamma-ray flares from the Crab Nebula, discovered in 2011 by the Agile and Fermi satellites.

2018-06-19
16:15
Interstellar grains analysed by the Cassini and Stardust space missions
Mario Trieloff (Inst. Geowiss., Universität Heidelberg, D)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
In 1992 the Ulysses spacecraft detected a stream of interstellar dust grains passing our solar system. The Stardust mission succeeded in collecting and identifying seven particles of likely interstellar origin. They are diverse in elemental composition, crystal structure, and size. The presence of crystalline grains and multiple iron-bearing phases, including sulfide, in some particles indicates that individual interstellar particles diverge from representative models of interstellar dust inferred from astronomical observations and theory, but the relatively large grains found are biased to the high mass tail of the interstellar population and may not be truly representative. In-situ analyses of the Cosmic Dust Analyser on-board the Cassini spacecraft obtained between 2004 and 2013 yielded the first mass spectra of grains from the Local Interstellar Cloud. These 36 interstellar grains can be clearly identified and distinguished from Saturn bound dust by their direction and high velocity, and their mean mass is consistent with the typical ISD size inferred from astronomical observations. Mass spectra and grain dynamics suggest the presence of magnesium-rich grains of silicate and oxide composition, partly with iron inclusions. Major rock-forming elements (magnesium, silicon, iron, and calcium) are present in approximately cosmic abundances, with only small grain-to-grain variations, but sulfur and carbon are depleted. The ISD grains in the solar neighborhood appear to be homogenized, likely by repeated processing in the interstellar medium.

2018-06-12
16:15
Multi-Messenger Astronomy with Ultra-High Energy Cosmic Rays
Karl-Heinz Kampert (Bergische Universität Wuppertal, D)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
The search for the sources of ultra-high energy cosmic rays (UHECR) is the prime motivation for operating high energy gamma-ray-, neutrino-, and cosmic ray observatories around the globe. Cosmic rays are observed to energies reaching beyond 10^20 eV but their sources cannot be identified easily because cosmic rays suffer deflections in galactic and intergalactic magnetic fields. High energy photons and neutrinos, expected as secondary particles from hadronic interactions at or near the sources, propagate without any deflection and would allow seeing the UHECR sources. However, photons can result also from pure electromagnetic processes and neutrinos did not exhibit any point source, yet. To advance the field, information from the three high energy probes is being combined and more recently, also gravitational waves were added for specific transient sources. In fact, last years first simultaneous observation of gravitational waves and electromagnetic emission from the neutron star merger GW170817 is generally considered the start of multi-messenger astronomy. In this talk, we shall highlight benefits from joint observations and we review some recent results, including the search for neutrinos from the neutron star merger GW170817, the study of cross correlations of neutrinos and UHECR, the first significant observations of anisotropies in the UHECR sky above 8 EeV, and evidence of an excess of arrivals from strong nearby sources at energies above 40 EeV.

2018-06-05
16:15
Molecular interactions in dilute media studied with fast ion beams in the Heidelberg Cryogenic Storage Ring
Andreas Wolf (MPI für Kernphysik, Heidelberg, D)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
A cryogenic electrostatic storage ring, the CSR, has been taken into operation at the Max Planck Institute for Nuclear Physics. With laboratory astrophysics studies as one of its goals, the machine was built to store fast ion beams in extremely high vacuum, screened against terrestrial thermal radiation, and over times reaching up to an hour. Through the few-Kelvin cryogenic environment and the extreme suppression of collisional perturbations, in contrast to other ion-trap arrangements, low-energy molecular excitations (rotation, low-frequency vibrations or isomeric conformations) can evolve freely and thermalize purely by radiation. Controlled interaction is applied to the circulating ions by laser radiation or by merged or crossed particle beams (electrons, neutral atoms). Event-by-event multi-fragment detection, even for neutral products, and the high accuracy of charged-particle current measurements enable reaction cross-section and branching ratio measurements. The presentation focuses on laboratory studies of rotational excitation in small molecular ions and on inelastic collisions of molecular ions with cold electrons (dissociative recombination and collisional (de-)excitation). First experimental results, planned studies on polyatomic species relevant in interstellar and circumstellar media, and further projects to study complex molecular ions will be addressed.

2018-05-29
16:15
The Planck view at the magnetized dusty interstellar medium
Francois Boulanger (Université Paris-Sud, France)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
Observations of Galactic dust are a highlight and a lasting legacy of the Planck space mission. Spectacular images combining the intensity of dust emission with the texture derived from polarization data have received world-wide attention and become part of the general scientific knowledge. Beyond this popular success, the dust maps are an immense step forward for Galactic astrophysics, greatly superseding earlier observations. Planck has provided us with the data needed to statistically characterize the structure of the Galactic magnetic field and its coupling with interstellar matter and turbulence. Planck multi-frequency observations have also opened a new perspective on interstellar dust, upsetting existing models. Futrhermore, the astrophysics of dust emission has become inter-connected to a paramount objective of observational cosmology: the quest for curl-like (B-mode) polarization of the cosmic microwave background expected to arise from primordial gravitational waves produced during the inflation era in the very early Universe. I will introduce these science topics and highlight key results and perspectives of on-going research.

2018-05-22
16:15
Type Ia supernovae: From explosions to cosmology
Kate Maguire (Queens University Belfast, UK)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
Type Ia supernovae are the incredibly luminous deaths of white dwarfs in binary systems. They play a vital role in chemical enrichment, galaxy feedback, stellar evolution, as well as being instrumental in the discovery of dark energy. However, what are their progenitor systems, and how they explode, remains a mystery. There is increasing observational evidence that there are multiple ways in which white dwarfs can explode. I will review the status of what we know about the stellar systems that produce Type Ia supernovae, as well as discuss the recently discovered zoo of peculiar transients that are also predicted to result from the explosions of white dwarfs, such as He-shell mergers, tidal disruption events, violent mergers. Distinguishing between these explosion scenarios and understanding their diversity is vital for producing the best samples for future precision measurements of the cosmological parameters.

2018-05-15
16:15
Pulsating variables as tracers of the galaxy formation.
Giuliana Fiorentino (INAF Bologna, Italy)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
We will review the role of classical variables crossing the Instability Strip in our understanding of galaxy formation and evolution. We will discuss the fundamental role of photometric surveys of resolved stellar populations in our Galaxy and beyond. We have recently analysed the old stellar populations, as traced by RR Lyrae stars, observed in low density environments such as the Galactic halo and dwarf galaxies surrounding the Milky Way. This investigation has revealed that small satellites can not have had a major role in building up this old component of the Galaxy, whereas the contribution of more massive dwarf galaxies like the Large Magellanic Cloud (LMC) and/or the still merging Sagittarius dwarf spheroidal galaxy can be significant. In the near future thanks to Gaia and to the Large Synoptic Survey Telescope these kind of studies will gain much more detail and will be largely extended to the the outskirts of our Local Group (distances 1Mpc).

2018-05-08
16:15
Understanding the solar chromosphere
Jorrit Leenaarts (Department of Astronomy Institute for Solar Physics, Stockholm Univ., SE)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
The chromosphere is the interface between the interior of the Sun, where its magnetic field is generated, and the hot outer corona that drives the solar wind and causes space weather. It is difficult to understand: the chromosphere is the interface where the dynamics change from gas-pressure driving to magnetic-force driving, radiation transport changes from optically thick to optically thin, the gas state changes from neutral to ionised and from local thermodynamic equilibrium (LTE) to non-equilibrium conditions, and the MHD approximation is not sufficient to fully describe its physics. In this talk I will give an overview of the major open questions on understanding the solar chromosphere, and dicuss how observations, simulations, and advanced analysis tools can be used to shed light on these questions.

2018-04-24
16:15
Weak lensing by large-scale structure as an accurate probe of cosmology and much more!
Henk Hoekstra (Sterrewacht Leiden, NL)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
Weak lensing by large-scale structure is one of the most promising techniques to learn more about the nature of dark energy by mapping the dark matter distribution in the Universe as a function of distance. Weak lensing has also developed into the main tool to determine cluster masses, critical for their use for cosmology, but can also be used to study the dark matter halos of galaxies.I will review the recent progress in this active area of research and discuss the prospects for future projects, such as Euclid.

2018-02-06
16:15
Gravitational-wave emission and their multi-messenger signatures
Alessandra Buonanno (MPI Gravitationsphysik, Potsdam)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
The detection of gravitational waves has opened a new era of scientific discovery, as it permits a new kind of observation of the cosmos, quite different from electromagnetic and particle observations. In this talk I will review the gravitational-wave signals detected up to now by LIGO and Virgo, and discuss the theoretical groundwork that allows to identify and interpret those signals. I will also highlight how those new astronomical messengers are unveiling the properties of the most extreme astrophysical objects in the universe and probe fundamental physics.

2018-01-30
16:15
Black holes in the era of gravitational wave astronomy
Frans Pretorius (Perimeter Inst., Princeton, USA)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
Black holes are one of the more astonishing predictions of the theory of General Relativity. The Schwarzschild black hole solution was discovered within months of Einstein publishing the field equations of general relativity, though for decades after was regarded more as a mathematical curiosity than a plausible description of any real object in the universe. This began to change in the 1960's, both through theoretical and observational discoveries, and finally in 2015 the LIGO gravitational wave detectors found the first direct evidence for the existence of black holes, having measured a signal consistent with the inspiral and merger of two black holes. In this talk I will give an overview of black holes in general relativity, the LIGO observations, and what we can hope to learn about black holes in the coming decade as a plethora of new data is gathered from ground based gravitational wave detectors, the Event Horizon Telescope, and pulsar timing arrays.

2018-01-23
16:15
The circumgalactic medium of high redshift galaxies in emission
Lutz Wisotzki (Leibniz Institut für Astrophysik, Potsdam)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
I present observations with the MUSE instrument at the ESO-VLT that reveal the ubiquitous presence of extended Ly-alpha emitting envelopes around individual normal (non-AGN) galaxies at redshifts z > 3. These haloes are larger by factors of ~3-20 than the corresponding rest-frame UV continuum sources as seen by HST. Between ~20% and >~95% of the observed total Ly-alpha flux comes from the extended halo component. At the sensitivity level provided by MUSE, a large fraction of the field of view is actually covered with Ly alpha emission from redshifts 3 < z < 6, and I present a spectacular colour image visualising the "Sky in Ly-alpha". Our observations provide direct insights into the spatial distribution of at least partly neutral gas in the circumgalactic medium of low to intermediate mass galaxies at z > 3. I also discuss some implications for the demographics of high-redshift galaxies.

2018-01-16
16:15
Black hole mass growth across cosmic time: Insights from radio surveys
Vernesa Smolcic (Univ. Zagreb)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
Understanding how galaxies form and evolve through cosmic time, and how these processes are influenced by active galactic nuclei (AGN) are important goals of modern astrophysics. In this context, “radio-mode AGN feedback” is a regular ingredient in cosmological models, yet from an observational perspective still rather poorly understood. It is considered to be a key feedback mechanism, related to central supermassive black hole mass growth, at work in the latest phases of massive galaxy formation, and controlling the galaxy’s stellar mass build-up. Over the past decades our understanding of radio AGN was significantly advanced by panchromatic look-back sky surveys, and we have recently entered a “golden age” of radio astronomy thanks to upgraded and new facilities delivering now an order of magnitude increase in sensitivity. The VLA-COSMOS 3 GHz Large Project is based on 384 hours of observations with the upgraded, Karl G. Jansky Very Large Array (VLA) at 3 GHz (10 cm) toward the two square degree COSMOS field. The survey, reaching a median rms of 2.3 uJy/beam over the two square degrees at an angular resolution of 0.75′′, contains 10,830 radio sources down to 5 times the rms. It simultaneously provides the largest and deepest radio continuum survey at such angular resolution to-date, bridging the gap between last-generation and next-generation radio surveys. These radio data, in conjunction with the panchromatic COSMOS data sets, allowed us to study the physical properties, composite nature (i.e., star-formation vs. AGN related contributions to the total radio emission of the sources), and cosmic evolution of radio AGN out to a redshift of about 6, which can directly be linked to the radio-mode feedback, as postulated in cosmological models.

2018-01-09
16:15
Nucleosynthesis and the origin of stardust grains
Maria Lugaro (Konkoly Obs., HU)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
Sixty years ago the picture of the production of the elements in stars was established with the eight nucleosynthetic processes that still represent the basis of this research field. I will describe the birth of stellar nucleosynthesis, the production of the chemical elements in stars, and the observational constraints coming from stellar spectroscopy and from the laboratory analysis of stardust grains extracted from meteorites, as well as the differences between the two. Finally, I will show how recent progress in the laboratory analysis of extra-terrestrial samples has allowed the discovery of tiny but unmistakable signatures of stellar nucleosynthetic origin even in bulk materials in the Solar System, from the Earth to different types of meteorites. These signatures must have been carried by the original stardust grains and their sorting can potentially give us new information on the evolution of the protoplanetary disk.

2017-12-19
16:15
Cassini at Saturn: Mission accomplished
Tilmann Denk (Univ. Berlin)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, Grand Lecture Hall -- NOTE: There will be Glühwein and Cookies before the colloquium!
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Abstract
After two decades of flying through space and more than 13 years orbiting Saturn, the journey of the Cassini spacecraft ended in mid-September with an intended crash into the atmosphere of the ring planet. The months before brought an absolute highlight: In the "Grand Finale" of the mission, Cassini crossed the narrow gap between the rings and the atmosphere of the planet 22 times. What has the spacecraft experienced in these 20 years and especially in the Grand Finale, what have we learned about Saturn, its rings and the numerous moons? After having worked with Cassini throughout its entire journey, I will give you a small insight into the most interesting and exciting events and results, garnished with images of huge storms, complex ring structures, intricate tectonics, Germany-sized seas of methane, water eruption "plumes" hundreds of kilometers high, gigantic mountains, objects that look like flying saucers, or in short: pictures of Saturn, its rings and its moons.

2017-12-12
16:15
Charting new physics territories with time-domain astronomy
Ariel Goobar (Univ. Stockholm)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
The accelerated expansion of the Universe, attributed to the existence of dark energy, was discovered nearly two decades ago using distance measurements of Type Ia supernovae. To find the supernovae, image differencing was used targeting small parts of the sky, with just several thousand galaxies observed a few weeks apart. Since then, technological advances have allowed us to drastically increase the science reach of time-domain astronomy: the new generation of optical cameras can image the entire observable sky in a single night. We are starting to discover very rare phenomena, and to explore new time scales for transient phenomena, allowing us to chart new physics territories.

2017-12-05
16:15
Zooming in on planet-forming zones of disks around young stars
Ewine F. van Dishoeck (Leiden Obs., NL / MPE Garching)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
Protoplanetary disks are the birthplaces of planets but the spatial resolution at long wavelengths has so far been insufficient to resolve the critical 5-30 AU region. The Atacama Large Millimeter Array (ALMA) now allows us to zoom in to nearby disks and determine the physical and chemical structure associated with planet formation. This talk will provide examples of recent work on observations and models of protoplanetary disks in various stages of evolution. Surveys of large numbers of disks provide insight into typical masses and sizes, revealing surprisingly weak gas emission. Special attention will be given to transitional disks, which are a subset of disks with evidence for sharp-rimmed cavities (gaps or holes). They are the best candidate sources for harboring just-formed giant planets. ALMA allows imaging of both the gas and dust in these disks, providing constraints on the properties of any young planets. Some prospects for JWST will be mentioned.

2017-11-28
16:15
Exoplanets and the search for extraterrestrial life
Ignas Snellen (Univ. Leiden, NL)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
Placing the solar system in the context of other planetary systems is one of the central objectives driving the study of extrasolar planets. One of the most fascinating questions in modern science is whether other life-bearing planets exist. In this talk I will review the current state of the art of exoplanet research and discuss future ways to probe biomarker gases in Earth-like exoplanets that could point to biological activity.

2017-11-21
16:15
The chemical composition of globular clusters throughout the Local Group
Søren Larsen (Univ. Nijmegen, NL)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
I will discuss results from our recent work on the detailed chemistry of globular clusters (GCs) in Local Group galaxies. This work is based on a combination of integrated-light spectroscopy at high resolution and resolved imaging with HST in colour combinations that are sensitive to light-element abundance variations. Through the resolved imaging studies, it is now clear that the abundance anomalies that are the hallmark of multiple stellar populations are not restricted to old GCs, but are also found in LMC/SMC clusters as young as 2 Gyrs. This rules out formation mechanisms that were unique to the high redshift Universe. More generally, we find that GCs in dwarfs are, on average, more metal-poor than those in larger galaxies, although no clusters more metal-poor than [Fe/H]\approx-2.5 have been found so far. Overall, a large fraction of the most metal-poor stars in dwarf galaxies tend to belong to GCs. This has important implications for scenarios that invoke heavy cluster mass loss to account for the large fractions of enriched "second-generation" stars in GCs, as well as for globular cluster disruption and its contribution to the field star populations in halos in general.

2017-11-14
16:15
Quasars in the epoch of reionization
Fabian Walter (Max Planck Institute for Astronomy, Heidelberg)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
A prime objective of observational astrophysics is to characterize the earliest sources in the first Gyr of the universe, and to peer into the cosmic times when the first stars, black holes and galaxies formed. Although galaxy candidates are now identified up to redshifts of about 10, their faintness typically precludes detailed studies of their nature. Quasars, on the other hand, are the most luminous non-transient sources known and can be studied in detail at the earliest cosmic epochs. The discovery and characterization of a statistically significant sample of quasars at z>6 is crucial to study the epoch of reionization. I will present our progress in building such a statistical sample, which led to tripling the number of these quasars in just the last three years. I will discuss the diverse range of physical properties of this quasar sample as well as our follow-up studies from optical to radio wavelengths, including a new quasar at a record redshift (z=7.5). In particular, recent observations with ALMA revealed the presence of far-infrared companions around the quasars, and provide key constraints on the spatially resolved properties of the quasar host galaxies. Through multi-line ALMA spectroscopy we can also derive first constraints on the physical conditions of the interstellar medium in the quasar hosts. I will also discuss the potential of future JWST observations.

2017-11-07
16:15
No Colloquium - Higgs Workshop at Phil 12
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Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, Philosophenweg 12

2017-10-31
16:15
No Colloquium - 500 Years of Reformation (public holiday)
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Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, Philosophenweg 12

2017-10-24
16:15
Quantum mechanics and stellar spectroscopy: towards accurate abundance analysis of late-type stars
Paul Barklem (Univ. Uppsala, Sweden)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
The measurement of stellar properties such as chemical compositions, masses and ages, through stellar spectra, is a fundamental problem in astrophysics, of importance to many fields (e.g. Galactic archeology, chemical evolution, planetary formation, etc.). I discuss progress in the understanding of atomic collision processes relevant to high-accuracy non-LTE analysis of late-type stellar spectra. In particular, to analyse spectra at accuracies approaching the 1% level, quantum mechanical effects such as electron transfer by tunnelling and spin transfer via the exchange interaction should be accounted for in modelling collision processes involving electrons and hydrogen atoms. Similar processes are also important in the relatively young field of non-LTE analysis of spectra of supernova ejecta, showing even larger effects than in stellar atmospheres.

2017-07-25
16:15
The centre of M31
John Magorrian (Oxford Univ., UK)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
M31 is the nearest large galaxy for which we have a dust-free multi-wavelength picture of its central regions. It presents some puzzles. The inner few parsecs are dominated by a double nucleus, which is most naturally explained by Tremaine's (1995) model of an eccentric disc of old stars around a supermassive black hole. A more recent surprise is the discovery of a very compact cluster of young stars around the black hole. I review ongoing work on the construction of a coherent picture of this system and compare it to the clusters found at the centres of other nearby galaxies.

2017-07-18
16:15
Characterising atmospheric turbulence for advanced optical astronomical observations
James Osborn (Durham Univ., UK)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
The next generation of 40 m class Extremely Large Telescopes (ELTs) are currently under construction. These vast instruments will enable new discoveries in all areas of astronomy and push forwards the boundaries of human knowledge. They will look further back in space and time to explore the early universe and shed light on unanswered questions such as dark matter and dark energy. They will discover and characterise extra-solar planets and potentially find habitable, or even inhabited, worlds. To fulfil these ambitious objectives these giant telescopes will be equipped with highly sophisticated adaptive technologies in order to counteract the detrimental effects of the Earth’s atmosphere. The characterisation of atmospheric optical turbulence is critical for advanced optical astronomical observations. This includes using data from Adaptive Optics (AO) systems, dedicated auxiliary instrumentation as well as forecasts from numerical models of the Earth’s atmosphere. Exploiting this hybrid approaches enables us to determine the vertical profile of the turbulence strength, velocity, outer scale as well as the local turbulence contained in the telescope dome. This detailed knowledge is vital for wide-field AO systems which are particularly sensitive to the vertical structure of these atmospheric parameters and for highly-complex systems such as extreme AO, where the varying atmospheric parameters have a significant impact on performance. Atmospheric turbulence characterisation is therefore required for modelling, monitoring and optimising AO instrumentation, enabling efficient operation of current sophisticated instrumentation systems as well as the future Extremely Large Telescopes.

2017-07-11
16:15
The Cosmic Nursery: Growth Spurting Galaxies and Baby Black Holes
Sadegh Khochfar (Univ. Edinburgh, UK)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
In my talk I will present and discuss recent results from high-resolution simulations on the formation of the first galaxies and how these influence their environment. I will take a close look at how black holes will be seeded in such an environment and how the escape fraction of ionizing photons from galaxies evolves. Results from these simulations have profound implications for future observational missions with e.g. the James Webb Space Telescope and I will discuss these.

2017-07-04
16:15
The Milky Way – evidence for Seyfert activity in the recent past
Joss Bland-Hawthorn (Univ. Sydney, Australia)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
The Galaxy's supermassive black hole is a hundred times closer than any other massive singularity. It is surrounded by a highly unstable gas disk so why is the black hole so peaceful at the present time? This mystery has led to a flurry of models in order to explain why Sgr A* is radiating far below (1 part in 108) the Eddington accretion limit. But has this always been so? Evidence is gathering that Sgr A* has been far more active in the recent past, on timescales of thousands of years and longer. The bipolar wind discovered by MSX, the Fermi gamma-ray bubbles, the WMAP haze, the positronium flash confirmed by INTEGRAL, are indicative of something truly spectacular in the past. But when and how did this happen? We present new evidence that the Galactic Centre was a full blown "active galaxy" just a few million years ago. We discuss the most likely scenario for this incredible event which can be seen today imprinted across the Galaxy.

2017-06-27
16:15
IllustrisTNG: The new frontier to understand the co-evolution of dark-matter and galaxies with cosmological simulations of structure formation
Annalisa Pillepich (MPIA, Heidelberg)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
I will describe the numerical efforts to simulate galaxies with the code AREPO across an unprecedented range of halo masses, environments, evolutionary stages and cosmic times. In particular, I will focus on the IllustrisTNG project, a collaboration among Heidelberg, Munich, New York and Boston. There we are aiming to simulate a series of three gravity+magnetohydrodynamics cosmological volumes (50, 100, 300 Mpc a side, respectively) capable of both resolving the inner structures of galaxies as small as the classical dwarfs of the Milky Way, as well as of sampling the large scale structure of the Universe with thousands among groups and clusters of galaxies. I will briefly review what is explicitly and empirically solved in gravity+magnetohydrodynamics simulations for galaxy formation in a cosmological context and what is required and what it means to “successfully” reproduce populations of galaxies which resemble the real ones. I will therefore show preliminary results from the IllustrisTNG simulations, by focusing on the assembly of the most massive structures in the Universe, the build up and characterisation of the faint stellar envelopes around galaxies, the connections of the latter to their host DM haloes, and our theoretical expectations for the distribution of dark matter (DM) and stars on large scales and within galaxies.

2017-06-20
16:15
On the front of exoplanet modelling: Interior structures and atmospheres
Isabelle Baraffe (Univ. Exeter, UK)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
I will present recent developments of exoplanet atmospheric dynamics based on state-of-the-art Global Circulation Models and will discuss basic assumptions performed previously in this field, in terms of radiative transfer treatment and of chemistry. I will show the importance of treating consistently non equilibrium chemistry in these atmospheres. I will also present a scenario to explain the radius inflation of hot Jupiters, providing a robust mechanism to explain this puzzle.

2017-06-13
16:15
Studying galaxies in three dimensions
Michele Cappellari (Oxford Univ., UK)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
For a century, galaxy studies have been based on two-dimensional images and spectra of their energy distribution obtained at a limited number of spatial locations on the galaxies. In the past decade, this kind of observations has been replaced by a new wave of instruments, which are able to obtain spectra at every location over the galaxies, producing a full three-dimensional view. I will give an overview of the new discoveries in our understanding of galaxy formation, produced by this observational revolution.

2017-06-06
16:15
Do we understand the cosmic dipole?
Dominik Schwarz (Univ. Bielefeld)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
The dipole of the cosmic microwave background (CMB) defines a reference frame for cosmology. Is is assumed since its discovery that the CMB dipole is caused by the proper motion of the Solar system. This hypothesis leads to the prediction that the corresponding Doppler shifts and abberation effects are universal to all frequencies. Thus the CMB frame is assumed to be the comoving frame of freely falling Friedmann observers, which is essential in the analysis of many cosmological observables such as the Hubble diagram. As any fundamental hypothesis, also the proper motion hypothesis must be tested. I present results from a suite of cosmic radio dipole measurements based on radio continuum catalogues across frequencies. We find that the cosmic radio dipole agrees with the direction of the CMB dipole within errors but has an excess in amplitude which increases with wavelength. The limitations and consequences of our finding are discussed.

2017-05-30
16:15
Frontier Problems in the Theory of Exoplanetary Atmospheres
Kevin Heng (Univ. Bern, Switzerland)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
The study of the atmospheres of exoplanets has evolved into a frontier topic in astronomy and astrophysics. In principle, these atmospheres encode information on the formation history of exoplanets, their gaseous chemical inventory, and whether they are habitable and/or inhabitable. In practice, there are a series of unsolved theoretical problems that need to be overcome before the promise of exoplanetary atmospheres is fulfilled. In this colloquium, I will review a selected subset of these problems, some of which are active topics of research within my group and research center. As a prelude, I will perform a concise, theorist’s review of the landscape of current and future observations, both from the ground and space. I will then discuss the following 5 problems: degeneracies in transmission spectra, cloudiness, 1D versus 3D models, geochemical cycles and biosignature gases. I will end by performing a concise, executive review of my new textbook (“Exoplanetary Atmospheres: Theoretical Concepts and Foundations”) by Princeton University Press. (The first student who comes up to me after the colloquium and demonstrates that he/she is a student will receive a free copy.)

2017-05-23
16:15
Cosmic Test Ban Violators: Classical Novae across the Spectrum
Steve Shore (Dept. of Physics, Univ. of Pisa; Astron. Inst., Charles Univ. Prague)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
For those whose tastes run to explosions, classical novae are a goldmine of physical processes whose study illuminates a broad range of comic objects: planetary nebulae and luminous blue variables in fast forward, supernovae in slow motion, and lots in between. I'll review some of the results of the last seven years of panchromatic observations and simulations that are the basis of the Nova Legacy Project, a coordinated benchmark study of every known subtype of nova from cm through MeV.

2017-05-16
16:15
Volume-density-driven star formation in the Galaxy
Genevieve Parmentier (ARI, Heidelberg)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
Properties of star-cluster forming regions are crucial to determining whether nascent clusters emerge of their gaseous cradle as bound entities, or whether they immediately contribute to the field star population. Thanks to the Spitzer, Herschel and Wide-Field Infrared Survey Explorer space telescopes, the characterization of cluster-forming regions has made a major leap forward. In particular, molecular clouds of the Solar neighbourhood have revealed a quadratic star formation relation. We demonstrate that such a star formation relation can be accounted for by a model in which stars form in centrally-concentrated molecular clumps with a constant star formation efficiency per free-fall time. The corresponding model consequences – (i) improved survivability of clusters after the expulsion of the residual star-forming gas, and (ii) smaller stellar age spreads in clusters formed out of higher-density gas -- are discussed. Forging ahead, we also explore the pitfalls which affect the comparison of the star-formation relation for nearby molecular clouds, at low gas surface density, with the star-formation relation for more distant compact molecular clumps, at high gas surface density.

2017-05-09
16:15
On the rare Stellar Marriages that live happily ever after to eventually merge as Binary Black Holes
Selma de Mink (Univ. Amsterdam, The Netherlands)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
Massive stars are nearly always found in close pairs when they are young. A very small fraction of these pairs stay together throughout their turbulent lives. They end their lives as a double black hole system. Their orbit slowly decays until, eventually, they coalesce. These mergers giving rise to such strong bursts of gravitational wave emission that they can be detected directly at earth. The gravitational wave detector LIGO has publicly announced two of such events at the time of writing as well as one candidate event. In this talk I will focus on the lives of the extreme progenitors of LIGO’s black holes and discuss what we are learning about the lives and deaths of the most massive stars.

2017-05-02
16:15
CARMENES: Searching for Blue Planets Orbiting Red Stars
Andreas Quirrenbach (LSW, Heidelberg)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
CARMENES is a radial-velocity survey with the 3.5m telescope on Calar Alto looking for terrestrial planets in the habitable zones of 300 nearby M dwarfs. A consortium of eleven German and Spanish institutions built a pair of stabilized high-resolution spectrographs especially for this project. I will explain the scientific and technical considerations underlying the instrument design, show some early science data, and discuss the astronomy program that will be carried out with CARMENES in the coming years.

2017-04-25
16:15
Intrinsically aligned galaxies in weak lensing data
Björn Malte Schäfer (ZAH, ITA Heidelberg)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
In gravitational lensing one commonly assumes that the intrinsic shapes of galaxies are uncorrelated and that any correlation in the shapes is due to correlated distortion in the weak lensing mapping: But in fact there are tidal interaction mechanisms that can make galaxy shapes intrinsically correlated. In my presentation I will discuss possible tidal interaction and alignment mechanisms for spiral and elliptical galaxies, how the details of the tidal interaction mechanism generates shape correlations as their signature, and how this contribution affects the measurement of cosmological parameters from gravitational lensing. Changing the perspective I will quantify how much about alignment and tidal interaction mechanisms can be learned from weak lensing data and how the two effects can be statistically separated. Finally, I will discuss the role of tidal interaction in the formation of haloes and how tidal interaction changes the mass distribution of haloes.

2017-02-07
17:15
Gaia 1992-2017: Twenty-five years of kinks & bends - and always uphill.
Ulrich Bastian (Astron. Rechen. Inst., Heidelberg (Germany))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
I will present a few selected aspects of the history and evolution of the Gaia project, from its very start up to its present status, including a short description of last September's "Gaia Data Release 1" and a little preview of the forthcoming, much more dramatic "Gaia Data Release 2". - Summary: Sisyphos is about to finally and definitely deposit his rock on the mountaintop.

2017-01-31
17:15
From gas to stars in galaxies
Adrianne Slyz (Univ. Oxford (UK))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
Despite differences in their cosmological life stories, galaxies follow a seemingly simple script for star formation: gas transforms itself to stars at a rate which depends on the average gas surface density of a galaxy. For years, galaxy formation simulations have exploited this simple global relationship to make stars, but nature is indicating that more than gas surface density is at play. Turbulence in the star forming gas appears to be key. I will describe the evidence for this and current theoretical ideas of how turbulence shapes star formation. I will then discuss attempts to capture the effect of turbulence on star formation in high resolution cosmological simulations of individual galaxies, which incorporate results from resolved molecular cloud simulations. Consequences for stellar feedback, galaxy mophology, interstellar medium structure and dynamics will be presented.

2017-01-24
17:15
Shedding Light on the Dark Cosmos through Gravitational Lensing
Sherry Suyu (MPA, Garching (Germany))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
Gravitational lensing provides powerful means to study dark energy and dark matter in the Universe. In particular, strong lens systems with measured time delays between the multiple images can be used to determine the "time-delay distance" to the lens, which is primarily sensitive to the Hubble constant. Measuring the Hubble constant is crucial for inferring properties of dark energy, spatial curvature of the Universe and neutrino physics. I will describe the ingredients and newly developed techniques for measuring accurately time-delay distances with a realistic account of systematic uncertainties. A program initiated to measure the Hubble constant to <3.5% in precision from gravitational lens time delays is in progress, and I will present the latest results and their implications. An exciting discovery of the first strongly lensed supernova has offered a rare opportunity to perform a true blind test of our modeling techniques. I will show the bright prospects of gravitational lens time delays as an independent and competitive cosmological probe.

2017-01-17
17:15
Galactic archaeology to its limits
Else Starkenburg (Leipniz Inst. Astrophys. Potsdam (Germany))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
The lowest metallicity stars that still exist today probably carry the imprint of very few supernova. As such, they represent our best observational approach to understand the First Stars. In this talk I will review the early (chemical) evolution of the Milky Way system from both modeling and observational perspectives. In particular, I will present results of the Pristine survey, a Franco-Canadian photometric survey of the Milky Way halo designed to efficiently decompose the metallicity structures of the Milky Way halo. I will show how we can use this great discriminatory power to hunt for the very rare extremely metal-poor stars (bearers of the chemical imprint of the first stars), to weed out contaminants around metal-poor dwarf galaxies, and to search for stellar structures in the halo.

2017-01-10
17:15
Molecular Gas, Star Formation and Galaxy Dynamics from z~2.5 - 0
Linda Tacconi (MPE, Garching (Germany))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
Comprehensive and systematic studies of star formation and the gas contents of galaxies during the epochs that are associated with the peak (z~1-3), and subsequent winding down (z<1) of star formation in the Universe are enabling us to illustrate the important role that cold gas, the fuel for star formation, has played in the assembly of galaxies across cosmic time. Modest sized surveys already provide robust molecular gas detections in hundreds to a few thousand star forming galaxies (SFGs), from redshifts 0-3. Furthermore, spatially resolved spectroscopy in both the (sub)mm and NIR wavelengths now enable us to study the detailed kinematics, star formation, and ISM properties in SFGs on few kpc scales. I will discuss the results from these surveys, and place them in the general context of galaxy formation and evolution.

2016-12-20
17:15
Physik, Astronomie und Raumfahrt in Entenhausen (in German)
Stefan Jordan (Astron. Rechen. Inst., Heidelberg (Germany))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
Anhand einiger von Carl Barks gezeichneter Berichte aus Entenhausen wird geprüft, ob die in unserem Universum gültigen physikalischen Gesetze (z.B. Massenerhaltung, Impulserhaltung, Energieerhaltung, 2. Hauptsatz der Thermodynamik, Gravitationsgesetz) auch auf "Stella Anatium", dem Planeten, auf dem sich Entenhausen befindet, Gültigkeit besitzen. Darüber hinaus wird auf einige Eigenschaften der näheren kosmischen Umgebung von Donald Ducks Heimatplaneten eingegangen, was dadurch erleichtert wird, dass dort Raumfahrt betrieben wird. Der Vortrag wird auf Deutsch gehalten. The talk will be given in German.

2016-12-13
17:15
Cosmology with Clusters of Galaxies
Jochen Weller (LMU, München (Germany))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal

2016-12-06
17:15
ALMA studies of dust-obscured starbursts in the distant Universe
Ian Smail (Inst. Computational Cosmology, Durham Univ. (UK))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
For more than two decades we have known of the existence of a population of very dusty, far-infrared luminous sources at high redshift. But until the commissioning of ALMA, many of the basic characteristics of these sources were unclear. I will discuss recent studies with ALMA which are beginning to penetrate the obscuration in these systems to allow us to understand their fundamental properties. I will also discuss their connection to the formation and evolution of the galaxy populations we see in the Universe today.

2016-11-29
17:15
Exoplanets@SAC: System architectures of exoplanet systems
Simon Albrecht (MIT, Cambridge (USA))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
Over the last twenty years astronomers have discovered thousands of planets orbiting other stars than our sun. Many of these exoplanets display characteristics very different from the planets in our own solar system. Among these are planets on very eccentric (highly elliptical) and highly inclined (oblique) orbits. At Aarhus University one of our research foci is on getting a better understanding of these characteristics by measuring the system architectures for systems ranging from hot-Jupiters to systems with mall multiple planets. I will explain our techniques and present some recent highlights. We also started studying planets showing Transit Timing Variations (TTV). Here we focus on systems which had not been fully characterized by the Kepler mission due to Kepler's limited life time. These systems we now continue to monitor using ground based telescopes.

2016-11-22
17:15
Unveiling the structure of planet-forming disks
Misato Fukagawa (Natl. Astron Obs. Japan, Osawa (Japan))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
I present the images of protoplanetary disks around intermediate-mass stars with ages of a few to several million years, collected from Subaru and ALMA. Disk spatial/density structure is an important key to understand how disks evolve possibly under mutual interaction with new-born planets. In our near-infrared observations, rich structures have been uncovered such as radial gaps and spiral arms in remnant envelopes or disks. The strong non-axisymmetry has also been found with ALMA in dust continuum for a few disks with wide gaps, suggesting localized accumulation of dust particles. Although the sample size is still very small (~10), gaps and non-axisymmetry seem common, implying that the significant fraction of disks harbor stellar/planetary-mass companions, or planet-forming activity is already triggered.

2016-11-15
17:15
The Galactic Centre: a template for understanding star formation and feedback in a high-pressure environment
Steve Longmore (John Moores Univ., Liverpool (UK))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
The unknown physics of star formation and feedback represent the main bottleneck in connecting the observable galaxy population to cold dark matter cosmology. Both physical processes are expected to vary strongly with galactic environment and across cosmic history. I will discuss recent progress in understanding the physics of star formation and feedback in the inner few hundred pc of the Milky Way — the Central Molecular Zone (CMZ) — an environment with gas properties very similar to those in starbursts and high-z galaxies, in which most stars in the Universe formed. Within our lifetime, the CMZ is the only such environment for which it will be possible to simultaneously resolve the gas properties down to the size scales of individual (forming) stars, while also tracing galactic-scale processes, making it a critical benchmark for studies of star formation, feedback, and the interstellar medium across cosmic time. I will focus on recent work seeking to explain a puzzling observational paradox: the vast majority of gas in the CMZ is underproducing stars by 1-2 orders of magnitude compared to empirical star formation relations and theoretical predictions, and yet at the same time a very small fraction of the gas is producing the most violent star formation events in the Galaxy. I will discuss the implications of these findings for environmentally (in)dependent star formation relations and theories. I will finish by outlining the details of a model linking the emerging, multi-scale picture of star formation and feedback to a more general understanding of the mass flows and energy cycles in galactic nuclei.

2016-11-08
17:15
Weak Gravitational Lensing by Large-Scale Structure
Hendrik Hildebrandt (Argelander Inst. Astron., Bonn)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
Gravitational lensing represents a unique tool to study the dark Universe. In the weak lensing regime small distortions in the images of galaxies caused by the large-scale structure can be detected over the whole sky. Measuring these coherent distortions yields cosmological insights complementary to other probes like the cosmic microwave background (CMB). Ongoing wide-field imaging surveys exploit this to come up with competitive constraints on important cosmological parameters. In this colloquium I will concentrate on recent results from the ongoing European Kilo Degree Survey (KiDS) and show a mild tension of these results with CMB measurements from the Planck mission. Possible future developments will be discussed that could help make cosmic shear measurements even more robust and lead to an answer to the question whether this tension is real or not. I will conclude with an outlook towards future missions like Euclid, LSST, and WFIRST.

2016-10-25
17:15
Cosmic Ray Feedback: Written on the Wind
Ellen Zweibel (Univ. Wisconsin-Madison (USA))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
Cosmic rays account for about 1/3 of the energy density in the interstellar medium of the Milky Way, and affect interstellar gas dynamics and thermodynamics significantly. Detection and modeling of nonthermal radio and gamma-ray emission from other galaxies and from galaxy clusters is making it possible to measure this fraction remotely and to test theories of cosmic ray acceleration and transport in other environments. I will discuss how cosmic rays are coupled to the ambient medium, assess where extensions of the coupling theory are needed, and show that the nature of cosmic ray coupling matters to the stability of interstellar gas and in driving galactic winds.

2016-07-26
17:15
How cosmic rays shape galaxies
Christoph Pfrommer (HITS, Heidelberg (Germany))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
Understanding the physics of galaxy formation is arguably among the most complicated problems in modern astrophysics. Recent cosmological simulations have demonstrated that feedback by star formation, supernovae and active galactic nuclei appears to be critical in obtaining realistic disk galaxies, to slow down star formation to the small observed rates, and to move gas and metals out of galaxies into the intergalactic medium. However the particular physical processes underlying these feedback processes still remain elusive. In particular, these simulations neglected cosmic rays and magnetic fields, which provide a comparable pressure support in comparison to turbulence in our Galaxy, and are known to couple dynamically and thermally to the gas. I will present our recent efforts to model cosmic ray physics in the cosmological simulation code AREPO and demonstrate that cosmic rays matter on all scales relevant for galaxy formation. Diffusive shock acceleration of cosmic rays at supernova remnants modifies the expansion velocity of the shock wave and the inclusion of cosmic-ray physics in models of the interstellar medium allows for self-regulated outflows from the star-forming disk. I will also present global simulations of galaxy formation that couple cosmic rays to the magneto-hydrodynamics and demonstrate how powerful galactic winds can be launched which reduces the available amount of gas for star formation. Finally, I will discuss the non-thermal radio and gamma-ray emission of Milky-Way like galaxies and how the next-generation instruments such as SKA and CTA can be used to infer properties relevant for galaxy formation.

2016-07-19
17:15
Dust evolution in the interstellar medium and the influence of dust on the dynamics in protoplanetary disks
Melanie Koehler (QMUL)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
Dust grains play a crucial role in many physical and chemical processes in the interstellar medium (ISM) and in protoplanetary disks (PPDs). In the ISM, dust properties influence, for example, the formation and temperature of the major molecules in molecular clouds. It is therefore important to characterise the grain size, structure, shape and material composition in all phases of the ISM. Observations of the dust SED and extinction give indication of the dust properties and how these properties change towards denser regions. Compared to the diffuse ISM the observed SEDs of these denser regions show a decrease in colour temperature, increase in spectral index and increase in emissivity at 250 μm. Based on the THEMIS dust model, these observations can be explained self-consistently with coagulation and accretion processes of dust in regions with Av<16. These evolutionary processes can also explain the observed core- and cloud-shine. In conclusion, the evolutionary processes and especially grain growth begins in denser regions of the ISM. The dynamics of PPDs depend on the chemistry and ionisation rate of the disk which is influenced by the abundance and properties of dust particles. Assuming different approaches to calculate the X-ray (and UV) ionisation rate and different chemical reaction networks including dust particles, the electron abundance and subsequently the Elsasser number are derived. The calculations show that non-ideal magnetohydrodynamic effects dominate the disk interior in the early stage of the disk and that dust growth and dust settling can lead to turbulences in the disk. The calculations further show that dust settling is strongly dependent on the properties of the dust particles.

2016-07-12
17:15
The Era of Large-Scale Cosmological Simulations: exploring large and small scales simultaneously
Mark Vogelsberger (MIT, Dept. Phys., Cambridge, MA (USA))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
Progress in our understanding of galaxy formation, improved numerical algorithms, and increased computing power have recently lead to a number of impressive large-scale hydrodynamical simulations, which are able to reproduce key observables of the local and higher redshift Universe. These simulations allow us, for the first time, to study the interplay between large-scale structure and galaxy formation in detail. I will present recent results of these efforts and discuss some successes and failures of them.

2016-07-05
17:15
Supermassive Black Holes: Feeding and Feedback
Andrew King (University of Leicester, UK)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
The centre of almost every galaxy contains a supermassive black hole. I review recent progress in understanding how this black hole influences its host galaxy, and how it gained its mass.

2016-06-28
17:15
A theoretical and computational challenge: learning about the Dark Universe from cosmological linear perturbations.
Julien Lesgourgues (Inst. for Theo. Particle Phys. and Cosmology, Aachen (Germany))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
Several recent progress on the theoretical side suggest that the Dark Matter, Dark Energy and maybe Dark Radiation sectors could have a richer phenomenology than expected a decade ago, and affect the evolution of cosmological perturbations in non-trivial ways, even on linear scales. To make the best use of current and future data, one needs to face several theoretical and computational challenges, not only at the level of N-body simulations, but also as far as linear scale simulations and data fitting are concerned. I will illustrate this with a few example, picked up especially in the Dark Matter sector.

2016-06-21
17:15
From large to small scales and back: the challenges of computational cosmology and galaxy formation
Romain Teyssier (Univ. Zürich (Switzerland))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
Computing the universe has been a very successful activity over the past decades. We have now entered the era of precision cosmology, and N body simulations have to face new challenges to be able to contribute to the discovery of new physics in the universe. On smaller scales, baryons play an important role, and our understanding of galaxy formation still remains very vague. Feedback processes play an fundamental role in setting up galaxy properties and how they impact their environment. Recently, galaxy formation simulations have gained complexity and realism, introducing new simulated processes like magnetic fields and radiation fields. Our hope is to shed light on fundamental processes in galaxy formation, and to estimate how they will feedback on the mater distribution on large scale, leading to a more accurate, unbiased measurements of dark matter and dark energy properties.

2016-06-14
17:15
Space-Based Microlensing: From Planets to Black Holes
Andrew Gould (Ohio State, USA & MPIA Heidelberg)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
Space-based microlensing was first proposed 50 years ago as means to measure the "microlens parallax" effect and so derive the distances to the lenses, which are usually unseen. However, it is only in the last 2 years that this idea has been implemented, first using Spitzer and then Kepler, with the aims of measuring the Galactic distribution of planets and measuring the properties of free floating planets, respectively. These campaigns have required radically new approaches to space-based observations and have already led to surprising discoveries unrelated to planets. Preparations are well under way for WFIRST, which will be roughly 25% devoted to microlensing. WFIRST will revolutionize our understanding of planets. Even though it is 100 times closer to Earth than Spitzer and Kepler, it will still yield microlens parallaxes. Using the subtle effects of astrometric microlensing, WFIRST will provide the first census of isolated black holes as well.

2016-06-07
17:15
Gravitationally imaging dark matter with strong gravitational lensing
Simona Vegetti (MPA, Garching (Germany))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
The cold dark matter (CDM) paradigm predicts that the dark matter haloes of galaxies are populated by a significant number of substructures, with a steeply rising mass function towards lower masses. In the Milky Way, however, of order 10^5 substructures are predicted inside the virial radius, whereas only a few have been so far observed. This poses a major challenge to the CDM paradigm. New and independent methods are, therefore, required to assess the level of mass substructure in galaxies in the Local Universe and beyond. Unfortunately, most of these small mass substructures are expected to be completely dark and therefore not directly observable. Strong gravitational lensing provides a unique opportunity to detect and quantify the smallest and faintest substructures at cosmological distances. Thanks to the combination of state-of-the art lens modelling tools and high angular resolution data, we are now able to probe the substructure mass function at a new low mass limit, where competing dark matter models differ by more than two orders of magnitudes. In this talk I will present the latest results and future perspective of substructure lensing.

2016-05-31
17:15
Cosmic Reionization: Theoretical Modeling and Challenging Observations
Benedetta Ciardi (MPA, Garching (Germany))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
With the advent of radio telescopes such as LOFAR, MWA, PAPER, a new observational window on the high-redshift universe has been opened. More specifically, we expect in the near future to be able to detect for the first time the 21cm signal from the diffuse Intergalactic Medium (IGM) prior to its full reionization and thus probe the "dark ages". In this talk I will discuss about the theoretical modeling of the reionization process, the observability of the associated 21cm signal and the efforts ongoing within the LOFAR Epoch of Reionization Working Group.

2016-05-24
17:15
Stellar rotation across the cosmic history: from first stars to present day star-planet interactions
Georges Meynet (Genf Obs. Switzerland)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal

2016-05-17
17:15
Simulating Cosmic Dawn: Predictions for JWST
John Wise (Georgia Institute of Technology, (USA))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
Cosmic structure forms hierarchically through smooth accretion and dark matter halo mergers. As a consequence, all galaxies are the product of the dozens of mergers over billions of years. However, one can ask, "What were the first stars and galaxies in the universe?" I will review the current state-of-the-art simulations of early galaxy formation, starting with the formation of the first stars, which are initially devoid of metals and are suggested to have a characteristic mass of tens of solar masses. I will then present results from a suite of cosmological radiation hydrodynamics simulations that focus on the transition from the first stars to the first galaxies. Each simulation captures the radiative and chemical feedback from 10,000 first stars, leading to the formation of a 10^8 solar mass galaxy only 500 million years after the Big Bang, which is detectable with the upcoming James Webb Space Telescope. We have found that the galaxy luminosity function flattens at UV magnitudes above -14 due to feedback effects, and I will present theoretical predictions for their photometry and effects from dust extinction. I will also demonstrate that these faintest galaxies are the primary driver of the reionization of the universe, only to be suppressed by photo-heating at later times, perhaps evolving into a subset of dwarf galaxies in the local universe.

2016-05-10
17:15
Spectroscopic Studies of Galaxies in the Reionisation Era
Richard Ellis (ESO & Caltech)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
Deep exposures with the Hubble Space Telescope (HST) have provided the primary evidence that star-forming galaxies were present in the first billion years of cosmic history. Sometime during this early period the intergalactic medium transitioned from a neutral gas to one that is fully ionized. How did this `cosmic reionization' occur and were star-forming galaxies responsible? Imaging of deep fields with HST's Wide Field Camera 3 in conjunction with Spitzer photometry and Keck spectroscopy has provided important new insight into understanding when reionization occurred and the role of early galaxies in the process. Recent Planck results on the optical depth of electron scattering to CMB photons provide complementary information. I will review this rapid progress in our understanding of the last missing piece in our overall picture of cosmic history and discuss the remaining challenges ahead of future facilities such as JWST and E-ELT.

2016-05-03
17:15
Rare Elements from the First Stars to Today
Ian Roederer (Univ. of Michigan, Dept. of Astronomy, Ann Arbor (USA))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
Understanding the origin of the elements is one of the major challenges of modern astrophysics. Elements along the bottom two-thirds of the periodic table---including arsenic, selenium, barium, europium, lead, thorium, uranium, and others---are mainly produced by neutron-capture reactions. Some had not been detected previously in late-type stars, and the origins of all are not fully understood at present. My work focuses on abundances derived from ultraviolet and optical high-resolution spectroscopic data of dwarf galaxies, globular clusters, and field stars in the stellar halo. I will present recent observations of these elements that successfully muddy our understanding of when and how they were first produced in the early Universe.

2016-04-26
17:15
The Rosetta/Philae mission to comet 67P/Churyumov-Gerasimenko
Harald Krüger (MPI for solar system research, Göttingen)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
Comets are among the oldest remnants left over from the beginning of our solar system about 4.6 billion years ago. They are considered key in understanding this very early phase. In August 2014 the European spacecraft Rosetta encountered its target comet 67P/Churyumov-Gerasimenko and became the first artificial satellite of a cometary nucleus. Rosetta carried the lander spacecraft Philae on board which landed on the surface of the comet nucleus on 12 November 2014. Both, the lander Philae and the Rosetta orbiter have studied the comet in unprecedented detail. In the talk I will give an overview about the Rosetta mission, its scientific goals and the results achieved so far.

2016-02-02
17:15
A PHAT New Measurement of the High-Mass IMF
Daniel R. Weisz (UC Berkeley)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
The initial mass function (IMF) for stars above ~1 Msun is essential to testing and validating theories of star formation, constraining chemical enrichment models, the frequency of core-collapse supernovae, and interpreting the stellar populations of galaxies across cosmic time. Yet, despite more than 60 years of research, observational constraints on the high-mass IMF remain remarkably uncertain. Widely used high-mass IMFs (e.g., Kroupa) have associated uncertainties approaching an order-of-magnitude, making it virtually impossible to determine if the high-mass IMF varies with respect to environment (e.g., metallicity or star formation intensity) or is “Universal". In this talk, I will present the most precise measurement of the high-mass IMF to date. Using ~100 young, resolved star clusters in M31 imaged as part of the Panchromatic Hubble Andromeda Treasury (PHAT) survey, we find the high-mass IMF slope to be Gamma=1.45+/-0.03. Compared to the canonical Kroupa IMF (Gamma=1.3+/-0.7), the high-mass IMF in M31 is 0.15 dex steeper (i.e., fewer massive stars) and represents a factor of ~20 improvement in precision. There are no significant trends between the cluster IMF slopes and their ages, masses, and sizes, indicating that the IMF is remarkably “Universal” in this sample of ~100 clusters. I will illustrate some of the broader implications of a steeper IMF slope (e.g., on star formation rate indicators, core-collapse supernovae rates) and will conclude by discussing the prospects for precision IMF measurements in other environments.

2016-01-26
17:15
Cosmic Rays: from sources to Earth
Pasquale Blasi (Arceri Astrophys. Obs. Firenze (Italy))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
The quest for the origin of cosmic rays is more than a century old now. I will discuss some of the reasons why it is taking that long to figure out the answer to this problem. The simple picture of supernovae as sources and diffusion as a paradigm for transport seems to work well. Yet, the validity of many of the underlying assumptions of such an easy picture are questionable and the phenomenology arising from recent observations is getting too rich to be accommodated in these simple models. I will make an attempt at looking at the problem from the point of view of the basic physical elements that both acceleration and transport of cosmic rays rely upon and use this background to show that there is a rich phenomenology that arises from introducing basic principles, whenever possible, into the game. Sometimes this approach helps confirming and sometimes challenges the simple models of acceleration and transport that have been proposed through the years. Present and future observations will be discussed as tools to understand which way to go at the crossroads ahead.

2016-01-19
17:15
Regulation of Star Formation in Galactic Disks
Eva Schinnerer (MPIA, Heidelberg (Germany))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
Understanding the processes that regulate the formation of stars within galaxies is one of the major themes in current astrophysical research. Giant Molecular Clouds (GMCs, size ~ 50pc) are thought to play a critical role in these processes as they host most of the massive star formation occurring in our Galaxy. Detailed observations on scales of clouds can provide important insights on the properties of the star forming interstellar medium and conditions promoting the formation of massive stars. Using such detailed studies of the nearby grand-design spiral galaxy M51 as part of the Pbdi Arcsecond Whirlpool Survey (PAWS) as an example, I will present our current understanding of how the interstellar medium, its molecular component in particular, and star formation relate across galactic disks.

2016-01-12
17:15
The gamma-ray Universe
Stefan Funk (Phys. Inst., Erlangen)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
The field of gamma-ray astrophysics has received considerable attention in recent years. This is in part due to the success of the combination of satellite-based instruments such as Fermi-LAT coupled with Imaging Atmospheric Cherenkov Telescopes (IACTs) like H.E.S.S. measuring gamma-rays over a remarkably large energy range from several 10s of MeV to beyond 100 TeV. These observations demonstrated that the Universe is populated by numerous exotic and violent phenomena. The astrophysical objects from which we detect gamma rays generate enormous amounts of energy and accelerate particles to energies way beyond those accessible in human-made accelerators. The gamma-ray observations have also demonstrated, that they provide serious constraints on the annihilation cross section of dark matter in situ. In this talk I will describe the status and the future potential of gamma-ray observations of the Universe.

2015-12-22
17:15
The end of the Cretaceous: the causes for the dinosaur extinction 65 Myr ago
Christina Ifrim (Inst. Geowiss., Heidelberg (Germany))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
The Cretaceous period ended ca. 65 Myr ago with one of the largest mass extinctions known in Earth history. Dinosaurs, ammonites and many other groups of organisms were eliminated forever from our planet. The causes for this severe overturn on Earth have been under vivid debate for 35 years now. The discussion was initiated with the widely known hypothesis that the crisis was the consequence of a bolide impact. But what is the geological evidence for such a hypothesis? Can a global extinction event be triggered by impact alone? And is that all that happened at the end of the Cretaceous? This talk gives you insight into the origin of the impact scenario, but also to alternative explanations, and an update of the research on this extinction, which is far from being explained.

2015-12-15
17:15
Star and Planet Formation with the Atacama Large Millimetre/submillimetre Array
Leonardo Testi (ESO,Garching)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
ALMA is the leading facility for the observations of the cool Universe (and not only). After two decades of design and construction, this unique and transformational observatory has started Early Science operations four years ago and is now about to enter the Full Science phase. In this talk I will give an overview of ALMA , its capabilities and long term upgrade plan, which will maintain it a world leading ground based observational facility for at least two deacades. While giving an overview of the observatory and its capabilities, I will mostly focus on its contributions to our understanding of the star and planet formation processes.

2015-12-08
17:15
Supermassive Black Holes: From Jets to the Event Horizon
Silke Britzen (MPI Radioastronomie, Bonn (Germany))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
Highest resolution Event Horizon Telescope (EHT) observations will probably soon tell us more about the supermassive black hole at the Galactic Centre (Sgr A*) and the cores of nearby Active Galactic Nuclei (AGN). It might also help to clarify the long-standing question whether the central massive objects in AGN are instead close pairs of black holes. Mergers of supermassive black hole pairs are expected to generate the strongest gravitational wave signals. I will present examples of how we identify potential close binary black hole candidates based on the combined analysis of high resolution radio interferometric (VLBI) observations and multi- wavelength data. I will also provide an outlook on the scientific prospects with regard to future EHT-observations.

2015-12-01
17:15
Convection and rotations in stars
Steven Balbus (Dept. Phys., Univ. Oxford (UK))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
The internal rotational profile of the Sun is now known with great accuracy. The results initially were a great surprise. A dominant pattern of rotation on cylinders was expected, but instead, the dominant feature in the bulk of the convective zone was found to be rotation on cones of (nearly) constant latitude. At the base of the convection zone, strong radial shear---the so-called tachocline---is present. In this talk, I will show how these apparently surprising properties follow from a few simple ideas, and discuss predictions for asteroseismology measurements.

2015-11-24
17:15
How much iron is in our stars ?
Karin Lind (Dept. Phys. & Astron., Uppsala Univ. (Sweden))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
The spectra of cool stars are filled with lines of atomic iron, to the extent that the stellar [Fe/H] if often used as a proxy for the entire metal content of stars. Further, the excitation and ionisation balance of neutral and singly ionised iron is often used for determination of reddening-free stellar parameters. Together this makes [Fe/H] arguably the most important parameter for Galactic archaeology. Recent years have seen parallel developments of atomic data, stellar atmospheric modelling, and spectrum synthesis tools, culminating in a very important milestone; iron abundance analysis no longer requires calibration of free parameters. I will discuss the consequences that accurate iron abundances have for studies of chemical evolution.

2015-11-17
17:15
Learning about the Dark Matter with stellar streams
Vasily Belokurov (Inst. Astron., Univ. Cambridge (UK))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
Stellar streams can be used to measure the properties of the gravitational potential of the Milky Way. Impressively, such hard-to-get parameters as the halo concentration, its shape, even the lumpiness of the Galactic Dark Matter distribution can all be accurately constrained. In principle. However, there are curious complications along the way.

2015-11-10
17:15
Galaxy Formation at its Peak
Avishai Dekel (Racah Inst. Phys., The Hebrew Univ., Jerusalem (Israel))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
The most active phase of galaxy formation, during the first few Gigayears of cosmic history, is optimal for a study of the key processes that drive galaxy evolution. In this phase, massive galaxies at the nodes of the cosmic web are fed by intense streams including a smooth component and merging galaxies. This setting introduces new theoretical challenges, such as: (a) How do galaxies acquire the angular momentum that determines their structure? (b) What is the nature of the violent disk instability in high-z star-forming galaxies? (c) How do galaxies turn into compact star-forming “blue nuggets” with AGN? (d) What are the quenching mechanisms that lead to passive compact spheroidal “red nuggets”? (e) Why are the star-forming galaxies confined to a narrow Main Sequence? These issues will be addressed, based on cosmological simulations and analytic models, and their theoretical and observational implications will be discussed.

2015-11-03
17:15
Radiative Feedback and the Formation of Massive Stars and Clusters
Ralph E. Pudritz (McMaster Univ. Hamilton (Canada))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
The formation of massive stars and their accretion disks remains one of the outstanding problems of star formation. For massive stars and clusters, radiative feedback is a key process that may limit their masses. I will discuss the physical problems and large body of work that has addressed these questions before turning to our own contributions. For massive star formation, we have developed a new hybrid radiative transfer code that operates in a full 3D, adaptive mesh environment that can, for the first time, follow heating of gas by both discrete stellar sources as well as by diffuse radiative background. We used it to simulate the formation of massive stars during the collapse of 30 to 200 solar mass cores. We find that forming massive disks undergo gravitational instabilities at some time during their formation that drive spiral waves and very high accretion rates onto the protostellar cores. It is at this time that radiatively driven bubbles and outflows are launched. There are no signs of any fallback of cooled material from the bubblesor that radiative feedback drastically limits stellar mass independently of the initial mass reservoir. We find that radiatively heated disks also do not undergo the fragmentation reported in earlier work. Our results compare well with the recent observations of massive disk properties around forming O stars. I will also present first results of our new work on radiative feedback simulations of the formation of young clusters in turbulent Giant Molecular Clouds and on how cloud structure affects this process

2015-10-27
17:15
Cosmological Calorimetry: The nature of the intergalactic medium and the photon underproduction crisis
Juna A. Kollmeier (Carnegie Science, Washington (USA))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
The Lyman alpha forest remains one of the most robust predictions of cosmological hydrodynamic simulations. Lyman alpha absorption lines have been used for decades to trace cosmic structures that -- only recently, with the exquisite sensitivity achievable with modern instruments -- are beginning to be detected in emission as well. I will discuss the predicted morphology of the Lyman alpha forest and the possibility of revealing this structure with Lyman alpha imaging surveys. The emission signal is dependent on the ionizing background radiation which, at high redshift, is well-understood and constrained. However, I will show that at low redshift there is a huge mismatch between our expectations and observations. I describe a factor of 5 discrepancy between the value of the photoionization rate required to match cosmological models of the z = 0 intergalactic medium to observations of the Lyman alpha forest and the value predicted by state-of-the-art models that account for the emissivity of stars and quasars over time. Examining potential resolutions to this problem, I will demonstrate that solving it requires, at minimum, a major revision of our thinking about the low redshift universe.

2015-10-20
17:15
Collapse and Star Formation in Self-gravitating Turbulent Fluids
Norman Murray (Canadian Inst. Theor. Astrophys., Univ. Toronto (Canada))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
Observations of star forming regions in the Milky Way have established that stars form in large molecular clouds or GMCs. The spectral lines of these GMCs are usually interpreted as the signature of turbulent motion. The kinetic energy in the turbulence is similar to the gravitational binding energy of the GMC. Work over the last decade, including research done in Heidelberg, suggests that stars form in converging flows in this turbulence. I will describe recent analytic and numerical work that has resulted in a detailed description of the evolution of such converging flows. I will show that the flows set up density structures that do not vary with time; the converging gas flows through fixed run of density onto a central star or star cluster. The collapse drives turbulent motions, resulting in deviations from Larson's Law (the size-linewidth relation), and slowing the inflow velocity below the free-fall rate. However, the infall velocity is proportional to the square root of stellar mass, resulting in a mass accretion rate that grows linearly with time.

2015-07-21
17:15
Life and Death of the First Stars
Alexander Heger (Monash Univ. (Australia))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
The first stars are unique not only in being first but also because of being first, they have a unique and pristine primordial initial composition, which can dramatically alter both their evolution, the way they die as supernovae, and their resulting nucleosynthesis. For example, the recently discovered most iron-poor star known, SM0313-6708, hints at some primordial production process of calcium that can only be found and seen in such pristine stars. Another example is that reduced mass loss and higher characteristic initial masses may lead to a population of pair instability supernovae that could produce a very unique abundance pattern. No direct observations of these stars are possible at this time, however, so our ability to study these early stars is limited to indirect measurements and numerical simulations, though possibly we might be able to observe some of their stellar deaths in the near future. Stellar forensics based on nucleosynthesis patterns preserved in subsequent generations of stars may be used to attempt reconstruction of the properties of these first stars. But in order to be able to use this tool, we need know what abundances were synthesised in these first generations of stars.

2015-07-14
17:15
MASSIVE Galaxies and Small Supermassive Black Holes
Jenny E. Green (Princeton Univ., (USA))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
I will discuss MASSIVE, an ambitious new integral-field survey of the ~100 most massive galaxies within 100 Mpc. Using integral-field spectroscopy covering 200 pc to 20 kpc scales, we are studying the assembly history of massive galaxies from the supermassive black holes at the center to the dark matter halos on large scales. I will then discuss black hole scaling relations over a large range in galaxy mass, using MASSIVE observations at the high end and megamaser disk galaxies at low mass. If time permits, I will discuss progress on survey planning for the Prime Focus Spectrograph.

2015-07-07
17:15
Evolved planetary systems around white dwarfs
Boris Gänsicke (Dept. of Phys., Univ. Warwick (UK))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
We know over 1500 extra-solar planets, and the past few years have seen a rapid expansion of the parameter space to wider ranges in host star and planet mass, as well as larger orbital separations. Consequently, the architectures of the known planetary systems are becoming increasingly diverse, and so does the entire field of exo-planets. The questions that the study of white dwarfs can address are: What is the future of the known exo-planetary systems as their host stars evolve of the main-sequence? And what will happen to the solar system once the Sun dies? How can we detect evolved planetary systems? And what can they teach us? The strong surface gravity of white dwarfs implies that metals will sink out of the photosphere on time-scales that are orders of magnitude shorter than their cooling ages, and therefore white dwarfs are expected to have either pure hydrogen or helium atmospheres. Yet, the existence of metal-polluted white dwarfs has been a conundrum for nearly a century. We know now that these white dwarfs are polluted by accretion of rocky debris, remnants of a former planetary system. With hindsight, this is may not come as too much of a surprise, as our Sun will eventually evolve in a white dwarf orbited by Mars, the outer planets, and hosts of asteroids - and a similar fate awaits many of the known exo-planetary systems! The photospheric abundances of these white dwarfs mirror those of the debris they accrete, hence we can directly, and accurately measure the bulk abundance of extra-solar planetary material. In zeroth approximation, the abundance pattern measured so far are overall similar to those of the terrestrial planets in the Solar system. At a closer look, there is evidence for a variety of thermal processing and possibly differentiation in the parent bodies, and even for the accretion of water. Perhaps most astonishing are the lower limits on the mass of the parent bodies that were accreted, ranging up to 1e24g, i.e. well above the most massive asteroids in the Solar system. These chemical abundance analyses are currently, and for some time to come, by far the most precise studies of extra-solar planetary material. These recent discoveries raise many new questions: what is the architecture of planetary systems on the post-main sequence? What type of planetary bodies are delivered to the white dwarf, and how? What is the long-term evolution of these systems? A suite of recent simulations gives a glimpse into some possible answers.

2015-06-30
17:15
The Fourth Paradigm of Science in Astronomy
Alberto Krone-Martins (Univ. of Lisboa (Portugal))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal

2015-06-23
17:15
Active asteroids: primordial ice, collisions, rotational breakup?
Jessica Agarwal (MPI für Sonnensystemforschung, Göttingen)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
The classical picture of small bodies in the solar system sees comets as volatile-rich, quickly evolving bodies, and asteroids as rather inert pieces of rock and regolith. In recent years, a growing number of known active asteroids have shattered the classical picture. These are small bodies on orbits typical of asteroids, but displaying dust comae and tails similar to comets. Currently, 1-2 new objects are discovered per year, each of which bears new surprises. The population of active asteroids is characterised by great diversity, suggesting that asteroidal dust activity can have a number of different causes, like sublimation of hidden volatiles, collision, or rotational break-up. The talk will give an overview of the currently known population of active asteroids, introduce possible activation mechanisms, and discuss implications for our understanding of asteroids and dust in the solar system.

2015-06-16
17:15
Black Holes on the Computer
Thomas Baumgarte (Bowdoin College, Main, USA)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
Black holes are among the most fascinating predictions of Einstein's 100-year-old theory of general relativity. They are also among the most promising sources of gravitational radiation, which we hope to detect very soon. With a remarkable breakthrough in numerical relativity it has become possible to simulate the merger of binary black holes, and to predict the emitted gravitational wave signals. I will review some of the problems that these calculations presented, as well as their solutions, will report on some of the surprising astrophysical implications of these new simulations, and will outline some current and future challenges.

2015-06-09
17:15
Acceleration of particles in astrophysical shocks
Anatoly Spitkovsky (Dept. Phys.& Astron., Princeton Univ. (USA))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
Collisionless shocks are ubiquitous throughout the Universe, and are thought to be responsible for the generation of nonthermal particles that span many decades in energy. These particles are observed through synchrotron radiation from astrophysical sources, or directly as energetic cosmic rays. The main acceleration mechanism is known as diffusive shock acceleration, and involves particle scattering and diffusion around a shock wave. Despite its fundamental importance in astrophysics, the details of this mechanism and the conditions for its operation are only now coming to light, thanks to the advent of ab-initio numerical simualtions of collisionless shocks. I will review the progress in kinetic simualtions of shocks, and concentrate on results of the numerical survey of shock parameters, which allows us to understand the efficiency of shock acceleration, associated magnetic field amplification, and the physics of injection of ions and electrons into the acceleration process. These results can be applied to a number of astrophysical scenarios, including nonthermal emission from supernova remnants, jets in active galaxies, and gamma-ray bursts.

2015-06-02
17:15
Are supernova remnants the dominant sources of Galactic cosmic rays?
Jacco Vink (Univ. Amsterdam (NL))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
Supernova remnants have long been recognised as the most likely sources of Galactic cosmic rays. Indeed, studies carried out over the last 10-20 years have shown that supernova remnants do indeed accelerated particles to very high energies of 10-100 TeV. However, for supernova remnants to be the sources of Galactic cosmic rays they should be able to transfer 10% of their kinetic energy to cosmic rays, and accelerate them to at least 3x10^15 eV. In particular this last requirement is at odds with both observational constraints and with our theoretical understanding. I will review where we stand in our knowledge of particle acceleration in supernova remnants, based on multiwavelength data, and I will discuss a promising alternative for the origin of cosmic rays: super bubbles.

2015-05-26
17:15
(1) Are planetary systems flat? (2) Is statistical mechanics useful for describing the distribution of planetary orbits?
Scott Tremaine (School of Natural Sci., Princeton (USA))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
(1) Laplace argued, correctly, that the small inclinations of planetary orbits implied that the solar system formed from a flat disk. The observational and theoretical evidence on whether extrasolar planetary systems are flat, however, is still ambiguous. I will discuss constraints on flatness from the Kepler spacecraft and other sources; Lidov-Kozai oscillations; and competing migration mechanisms for the formation of giant planets at small orbital radii. (2) I will describe a simple statistical model for the orbit distribution of terrestrial planets, based on the ansatz that the planets explore uniformly all of the stable region of phase space. The predicted properties are generally consistent with both N-body simulations and the Kepler catalog of extrasolar planets.

2015-05-19
17:15
Dust-obscured starbursts and their implications for galaxy assembly at early times
Caitlin Casey (UC Irvine, USA)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
Dusty star-forming galaxies (DSFGs) host the most intense stellar nurseries in the Universe. Although rare today, they were a factor of 1000 times more common at z~2 and likely contributed significantly to the buildup of the Universe’s stellar mass and the formation of high-mass galaxies. However, an ongoing debate lingers as to their evolutionary origins at high-z. While DSFGs locally are known to be merger-driven collisions of gas-rich disk galaxies, some works argue that high-z DSFGs have different origins, and could just be solitary massive gas-rich disks (continually fed star-forming fuel via the gas-rich IGM). Other conflicting evidence argues high-z DSFGs are major mergers, like their local cousins. Solving the debate, as to the origins of high-z DSFGs, requires a careful census and follow-up of DSFGs. I will describe some of the latest observational research on dusty, infrared-luminous galaxies at high-redshift. Specifically, I will focus on: 1. measuring the far-IR/submm contribution to the cosmic star formation rate density out to high-z, and compare it to the optical/UV contribution to infer the universal importance of infrared surveys out to early epochs, 2. observational tools we can use to surmise the physical mechanisms which drive intense star-formation, and 3. how these rare but extreme galaxies can be uniquely useful as probes of some of the most massive structures in the Universe’s cosmic web. My long-term goal is to understand the triggering mechanisms for star formation episodes in extreme, ultraluminous starburst environments, how they relate to star formation in more common ``Milky Way'' type galaxies at high-redshift, and what the implications are for galaxy evolution at very early times.

2015-05-12
17:15
New Data, new Methods: Chemodynamic Milky Way Models challenged by modern Surveys
Ralph Schoenrich (Dept. of Phys., Oxford (UK))
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
Galactic Astronomy is undergoing an unprecedented revolution. The Gaia satellite mission is measuring parallaxes for ~1 billion stars, outperforming its predecessor Hipparcos by 4 orders of magnitude in sample size and 2 orders of magnitude in precision and sample range. It is supported by ground based spectroscopic surveys collecting millions of high quality spectra. The first such data have already changed our understanding and interpretation of galactic structure, e.g. of the Galactic halo, and of galactic dynamics, like radial migration and the origin of the thick disc. I will outline the challenges in understanding these large surveys, give an outlook of the next years and discuss what new observations of the past year tell us about structure and history of the Milky Way.

2015-05-05
17:15
A microscopic approach to cosmic structure formation
Matthias Bartelmann (ITA)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
So far, the non-linear evolution of cosmic structures is accessible only for large-scale numerical simulations. The conventional analytic treatment of cosmic density fluctuations with the hydrodynamical equations runs into severe conceptual and technical difficulties even on moderately non-linear scales. As an alternative, we have developed a microscopic, non-equilibrium, statistical theory for cosmic structure formation which avoids these difficulties by construction and allows to enter deeply into the non-linear regime of cosmic density fluctuations. The theory also allows to unify approaches to kinetic theory and hydrodynamics, offering a joint treatment of dark and baryonic matter. I will motivate and introduce this theory in simple terms, show some results on non-linear cosmic structure formation obtained so far, and discuss some possible future applications.

2015-04-28
17:15
Extragalactic Archeology
Charlie Conroy (Harvard Smithsonian Center Astrophys., Cambridge)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
One of the primary avenues for understanding the formation and evolution of galaxies is through studying their stellar populations. A new generation of population synthesis tools that we have been developing are now capable of measuring an unprecedented amount of information from high quality spectra of galaxies. In this talk I will present results from an ongoing program aimed at measuring the stellar initial mass function, ages, and detailed elemental abundance patterns of early-type galaxies over the interval 0<z<1. Constraints on the abundances of the alpha, iron peak, and neutron capture elements offer the promise of reconstructing the detailed star formation histories of these now dormant galaxies. By measuring the evolution of these quantities through cosmic time we are gaining fresh insights into the assembly histories of galaxies. The techniques we are developing will enable `extragalactic chemical tagging' and, more generally, will open up the low resolution universe for detailed study

2015-04-21
17:15
Simulating the formation and evolution of the galaxy population
Simon White (MPIA Garching)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
Recent observations of the high-redshift universe have characterized the initial conditions for nonlinear structure formation over the full range of scales responsible for dwarf and giant galaxies, galaxy clusters and the large-scale cosmic web. At the same time, wide-field spectroscopic and photometric surveys have measured the abundance and clustering of low-redshift galaxies as a function of mass, size, morphology, kinematic structure, gas content, metallicity, star formation rate and nuclear activity, while deep surveys have explored the evolution of several of these distributions to z>3. Galaxy population simulations aim to interpret these observations within the LCDM structure formation paradigm, thereby constraining the complex, diverse and heavily interconnected astrophysics of galaxy formation. Recent simulations are broadly consistent with the galaxy abundances and clustering seen in both wide-field and deep surveys, and provide predictions for topics as different as galaxy-galaxy lensing, the triggering and duty cycles of AGN, and the evolution of Tully-Fisher, mass-size and mass-metallicity relations. They show galaxy assembly histories to be strongly constrained by the structure formation paradigm, giving insight into issues such as internally versus externally driven evolution, inflow versus winds, major versus minor mergers, in situ versus ex situ star formation, and disks versus bulges. In addition, simulations can now be adapted to represent any chosen LCDM-like cosmology, allowing a first assessment of whether galaxy formation uncertainties will limit our ability to do precision cosmology with galaxy surveys.

2015-02-03
17:15
Fundamental Physics from Gravitational Lensing
Allen Heavens (Imperial College)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, Großer Hörsaal

2015-01-27
17:15
The Search for Gravitational Waves
Bruce Allen (MPG-AEI)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, Großer Hörsaal
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Abstract
In 1916, Einstein predicted the existence of gravitational radiation, a fundamental consequence of his general theory of relativity. By the end of this decade, we expect to make the first direct observations of gravitational waves, using ground-based instruments (LIGO in the USA, VIRGO in Italy, GEO in Germany, KAGRA in Japan, LIGO in India). I describe the status and capabilities of the detectors, and discuss the different types of astrophysical sources which we hope to detect. We expect that the first direct detections of gravitational waves (perhaps as early as 2017) will be from the coalescence and merger of binary neutron star pairs. Such events may also be accompanied by electromagnetic gamma-ray bursts. I'll also talk about the longer-term perspectives, and describe how some of the new data analysis methods and technology developed for the gravitational wave search have benefited more conventional electromagnetic astronomy. For example in the past four years the volunteer distributed computing project Einstein@Home has discovered over fifty new radio and gamma-ray pulsars.

2015-01-20
17:15
The Cosmic Ionising Background: from the Reionsation Era to Present Days
Francesco Haardt (University of Milano)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, Großer Hörsaal

2015-01-13
17:15
Our Universe – Cosmological Results of the Planck Mission
Thorsten Enßlin (MPA)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, Großer Hörsaal

2014-12-16
17:15
Snowlines, Red Dwarfs, and Little Green Beings: A Cosmic Tale of Origins
Eric Gaidos (Hawaii)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, Großer Hörsaal
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Abstract
The search for Earth-size and potentially Earth-like planets around other stars has entered a new era with the achievements of the Kepler mission and the promise of new astronomical capabilities in space and on the ground. Tiny M dwarf stars and their planets have played an out-sized role in the success of this endeavor, but their study is only now catching up with those of their solar-mass cousins. I review recent advances in measuring the properties of these stars as they relate to understanding their planets. It has been proposed that M dwarf stars host most of the "habitable real estate" in our Galaxy and thus, in a speculative vein, I discuss the potential of their planets to host life and why, if they are such attractive locales, we do not find ourselves orbiting one.

2014-12-09
17:15
The Complex Ends of Galaxy Lives: Star Formation, Black Hole Feedback and the Fate of Gas Reservoirs
Kevin Schawinski (ETH Zürich, Switzerland)
Heidelberg Joint Astronomical Colloquium
Phil 12, gHS
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Abstract
Massive galaxies are broadly split into those forming stars on the main sequence, and those which are quiescent. The physical processes by which galaxies quench their star formation remain poorly understood. I analyze the properties of galaxies and track their evolutionary trajectories as they migrate from the blue cloud of star forming galaxies to the red sequence of quiescent galaxies via the `green valley'. I show that there must be two fundamentally star formation quenching pathways associated with early- and late-type galaxies which are intricately linked to how hydrogen gas reservoirs are destroyed or shut off. In the quenching of late-type galaxies, environment (or halo mass) is a key parameter, while for early-types, an internal mechanism such as black hole feedback is more likely. I will present recent HI observations supporting this picture.

2014-12-02
17:15
Observing Magnetic Fields in Galaxies and Prospects with the Square Kilometre Array
Rainer Beck (MPIfR)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, Großer Hörsaal
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Abstract
The strength and structure of cosmic magnetic fields can be well studied by observations of radio continuum emission, its polarization and Faraday rotation. Total field strengths in spiral arms and bars are 10-30 MicroGauss and hence are dynamically important. These probably are turbulent fields generated by turbulent gas motions. Fields with a well-ordered spiral structure exist in many types of galaxies. The strongest regular fields are found in interarm regions, sometimes forming 'magnetic spiral arms' between the optical arms. Faraday rotation measures of the polarization vectors sometimes reveals large-scale patterns which are regarded as signatures of coherent fields generated by dynamos. Polarization observations with the forthcoming large radio telescopes is opening a new era in the observation of magnetic fields and should help to understand their origin. Low-frequency radio synchrotron emission traces low-energy cosmic-ray electrons which can propagate further away from their origin. LOFAR (operating at 30-240 MHz) started to map the structure of weak magnetic fields in the outer regions and halos of galaxies and in the Milky Way. Polarization at higher frequencies (1-10 GHz), to be observed with the JVLA and the SKA, traces magnetic fields in the disks and central regions of galaxies in unprecedented detail. All-sky surveys of Faraday rotation measures towards a dense grid of polarized background sources planned the SKA and its precursor telescope ASKAP are dedicated to measure magnetic fields in distant intervening galaxies, clusters and intergalactic filaments. These surveys will also be used to model the overall structure and strength of the magnetic field in our Milky Way.

2014-11-25
17:15
Gas and Galaxy Evolution: From Voids to Clusters, Near and Far
Jacqueline van Gorkom (Columbia)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, Großer Hörsaal

2014-11-18
17:15
Has Dark Matter Finally Been Found?
Lars Bergstrom (Stockholm)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, Großer Hörsaal
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Abstract
In the last couple of years, several claims of hints of dark matter detection have been made. In this talk, I will give a brief review of the dark matter problem and present the large spectrum of theoretical particle candidate models, as well as their various detection methods. Current indications of dark matter detection will be discussed, and arguments both for and against the dark matter interpretation of these will be given. Finally, I will attempt to answer the question in the title.

2014-11-11
17:15
The Cradles of Planets – Turbulent Gas Disks around Young Stars
Hubert Klahr (MPIA)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, Großer Hörsaal
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Abstract
Planets are a beneficial side effect of star formation. They are believed to form in the dust rich gas disk around young stars. These essentially Keplerian disks have proven to be extremely stable to perturbations, when magnetic fields are not in operation, as we believe it is the case for large portions of a typical circumstellar disk. But disks around young stars are complicated entities - they share a lot of properties with planetary atmospheres and one can learn a lot from the stability of rotating stars. Disks around young stars have a radial temperature gradient driven by stellar irradiation, which leads to a thermal wind, e.g. vertical shear. In addition the temperature gradient leads to a height dependent radial stratification that can be radially buoyant. Without thermal relaxation these disks are linearly stable, but with the right amount of cooling and heating for instance by the radiative transport of heat, one can drive a Goldreich-Schubert-Fricke Instability (see for instance Nelson et al 2013) and a Convective Overstability (Klahr and Hubbard 2014; Lyra 2014). In this talk I present some recent results from linear stability analysis as well as from numerical experiments and discuss the consequences on the planet formation process and its observational signatures.

2014-11-04
17:15
Nuclear Star Clusters and Black Holes
Nadine Neumayer (MPIA)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, Großer Hörsaal
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Abstract
The centers of massive galaxies are special in many ways, not least because all of them are believed to host supermassive black holes. Since the discovery of a number of relations linking the mass of this central black hole to the large scale properties of the surrounding galaxy bulge it has been suspected that the growth of the central black hole is intimately connected to the evolution of its host galaxy. However, at lower masses, and especially for bulgeless galaxies, the situation is much less clear. Interestingly, these galaxies often host massive star clusters at their centers, and unlike black holes, these nuclear star clusters provide a visible record of the accretion of stars and gas into the nucleus. I will present our ongoing observing programme of the nearest nuclear star clusters, including the one in our Milky Way. These observations provide important information on the formation mechanism of nuclear star clusters. They allow us to measure potential black hole masses and might give a clue on how black holes get to the centres of galaxies.

2014-10-28
17:15
The Galactic Bulge: Current Perspective, New Surveys
Mike Rich (UCLA)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, Großer Hörsaal
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Abstract
The Galactic bulge of the Milky Way is the nearest spheroid, 100 times closer than the Andromeda galaxy. This offers a unique opportunity to investigate detailed kinematics, chemical composition, and structure for this population. Although the Lambda-CDM formalism gives a clear route to the formation of classical bulges, the Milky Way bulge appears to have formed from the secular evolution of a massive disk, a spheroid formation channel that does not easily follow from LCDM. A survey of 9,500 bulge M giants, the Bulge Radial Velocity Assay, showed that <10% of the bulge is in a classical slowly rotating bulge. The discovery that a strongly "X-shaped" component to the bulge is also present, strengthens the evidence for an extreme almost pure bar. Yet color-magnitude diagrams from HST, and composition, support an old, rapidly formed, bulge. We present new composition trends that support his picture and may also constrain the star formation history and initial mass function of the system. We also explore Terzan 5, a peculiar star cluster with multiple stellar populations, proposed as a fossil bulge "building block" stellar system. We will also present the plan for and early results from the Blanco DECam Bulge Survey, a six-color optical/infrared survey of the bulge, to map its structure as a function of age and metallicity.

2014-10-21
17:15
The Origin of the Stellar Initial Mass Function
Mark Krumholz (UCSC)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, Großer Hörsaal
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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, and over most of cosmic time. Explaining its origin and universality is one of the oldest problems in theoretical astrophysics, and a fully successful theory eludes us even today. In this talk, however, I describe recent progress toward an explanation for the mass scale of stars. This work is based on radiation-hydrodynamic simulations, which elucidate the way forming stars feed back on their environments and regulate the process of turbulent fragmentation that determines the IMF. Using insight from these simulations, I show that it may even be possible to express the characteristic mass of stars in terms of fundamental constants.

2014-07-22
17:00
Galaxies on FIRE: Stellar Feedback Explains Inefficient Star Formation
Philip Hopkins (Caltech Univ.)
Heidelberg Joint Astronomical Colloquium
Haus der Astronomy, Königstuhl, Auditorium
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Abstract
Many of the most fundamental unsolved questions in star and galaxy formation revolve around star formation and "feedback" from both massive stars and accretion onto super-massive black holes. I'll present new simulations which attempt to realistically model the diverse physics of the interstellar medium, star formation, and feedback from stellar radiation pressure, supernovae, stellar winds, and photo-ionization. These mechanisms lead to 'self-regulated' galaxy and star formation, in which global correlations such as the Schmidt-Kennicutt law and the global inefficiency of star formation -- the stellar mass function -- emerge naturally. Within galaxies, feedback regulates the structure of the interstellar medium, and many observed properties of the ISM, star formation, and galaxies can be understood as a fundamental consequence of super-sonic turbulence in a rapidly cooling, self-gravitating medium. But feedback also produces galactic super-winds that can dramatically alter the cosmological evolution of galaxies, their behavior in galaxy mergers, and structure of the inter-galactic medium: these winds depend non-linearly on multiple feedback mechanisms in a way that explains why they have been so difficult to model in previous "sub-grid" approaches. Finally, I'll discuss how missing physics in these models might change our conclusions.

2014-07-15
17:00
Planetary Science from the Top-Down: the Exoplanet Opportunity
Nick Cowan (Northwestern Univ.)
Heidelberg Joint Astronomical Colloquium
Haus der Astronomy, Königstuhl, Auditorium
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Abstract
What started as a trickle in the mid 1990's is now a torrent, with over one thousand extrasolar planets currently known, and thousands of candidates awaiting confirmation. The study of exoplanets has already revolutionized our view of planet formation, and will soon do the same to our understanding of planetary atmospheres and interiors. The diversity of exoplanets gives us the leverage to crack hard problems in planetary science: cloud formation, atmospheric circulation, plate tectonics, etc. However, the characterization of exoplanets presents a challenge familiar to astronomers: our targets are so distant that we only see them as unresolved dots. I will describe how we can extract spatially-resolved snapshots of planets from such observations. These data are sufficient to constrain low-order climate models and therefore give us insight into the effects of clouds, heat transport, and geochemical cycling. Coarse measurements for a large number of planets is the perfect complement to the detailed measurements possible in the Solar System. That is the exoplanet opportunity.

2014-07-08
17:00
The turbulent life-cycle of molecular clouds
Stefanie Walch (Uni-Köln)
Heidelberg Joint Astronomical Colloquium
Haus der Astronomy, Königstuhl, Auditorium
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Abstract
Apart from stellar feedback and self-gravityMolecular clouds are cold, dense, and turbulent filamentary structures that condense out of the multi-phase interstellar medium. They are also the sites of star formation. The minority of new-born stars is massive, but these stars are particularly important for the fate of their parental molecular clouds. I will present results from high-performance, three-dimensional simulations that show the formation and dispersal of molecular clouds within representative pieces of disk galaxies., we employ an accurate description of gas heating and cooling as well as a small chemical network including molecule formation and self-shielding. Gravitational collapse is compensated by stellar feedback, leading to the establishment of a dynamical equilibrium of the interstellar medium within the disk. I will discuss results for disks at different gas surface densities which e.g. demonstrate that the molecular gas mass fraction increases with gas surface density. Moreover, I will show that outflows generated by supernovae that explode within the parental molecular clouds may contain a significant fraction of diffuse molecular hydrogen that is not well traced by CO. These simulations will bring forth a modern paradigm for the full life cycle of molecular clouds with important implications for galaxy evolution.

2014-07-01
17:00
Very high energy gamma ray astronomy: from H.E.S.S. to CTA
Werner Hofmann (MPI Kernphys, Heidelberg)
Heidelberg Joint Astronomical Colloquium
Haus der Astronomy, Königstuhl, Auditorium
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Abstract
In the last decade, very high energy (VHE) gamma ray astronomy - at photon energies of 100 GeV and beyond - has developed in giant steps, with the number of known cosmic VHE gamma ray sources now well over 100. As the first system of large imaging atmospheric Cherenkov telescopes, the High Energy Stereoscopic System - H.E.S.S. - in Namibia has contributed significantly to this development. The talk will highlight some of the key results, and provide an outlooks towards the planned CTA observatory, aimed at boosting sensitivity by an order of magnitude compared to H.E.S.S.

2014-06-24
17:00
The chemistry of planet formation
Karin Öberg (CfA)
Heidelberg Joint Astronomical Colloquium
MPIA, Königstuhl, Auditorium
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Abstract
In the cold and dense stages of star and planet formation, volatile molecules condense out on interstellar grains forming icy mantles. The physics and chemistry of these ices may have a direct impact on planet formation efficiencies and planet bulk compositions. Ice chemistry is also expected to be the main formation site of complex organics in space and may thus regulate the prebiotic potential of nascent planets. We have used a combination of IR and millimeter observations, theory, and laboratory experiments to characterize interstellar ices, snow line locations (i.e. where these ices are located), and the chemical and planet formation consequences of the exact locations of different snow lines. I will discuss how the outcome of these studies have impacted our understanding of ice processes and of organic chemistry during star and planet formation, and also future prospects as complete ALMA and the next generation of laboratory experiments come online.

2014-06-17
17:00
Extracting science from surveys of our Galaxy: the balance between dark & light matter from the RAdial Velocity Experiment
James Binney (Oxford University)
Heidelberg Joint Astronomical Colloquium
Haus der Astronomy, Königstuhl, Auditorium
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Abstract
Huge observational resources are being devoted to the study of our Galaxy. Dynamical models of the Galaxy are key to the exploitation of data from these surveys, and the surveys in hand demand a step change in the sohistication of available dynamical models. I will review the state of this art and then discuss the application of the new methods to data for 200,000 giant stars observed by RAVE. These data enable us to split the matter that generates the gravitational field near the sun into dark and light components with negligible random error. The uncertainties are systematic and of order 10%. The dominant uncertainty is the distance scale of the sample, and this will be eliminated by Gaia in the next few years.

2014-06-10
17:00
Observing the Dark Universe
Catherine Heymans (Inst. Astron., Univ Edinburgh)
Heidelberg Joint Astronomical Colloquium
Haus der Astronomy, Königstuhl, Auditorium
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Abstract
Dark Matter and Dark Energy constitute over 95% of the energy density of the Universe, and determining the nature of the Dark Universe is one of the major challenges for science over the next decade. Weak gravitational lensing is a powerful technique that can map dark matter structures from its gravitational effects alone and probe dark energy through its effect on the growth of these structures. From an observational prospective, I'll discuss the challenges and successes of this unique technique, presenting results from the completed Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS) and the new ESO-VST Kilo-Degree Survey (KiDS). These surveys probe dark matter in galaxy haloes and galaxy clusters and constrain cosmology through the detection of weak lensing by large-scale structures. In combination with galaxy redshift surveys, lensing also provides a unique test for whether we need to go beyond Einstein with our current model of gravity.

2014-06-03
17:00
Making gold in core-collapse supernovae and neutron star mergers
Almudena Arcones (Inst. Kernphys, TU Darmstadt)
Heidelberg Joint Astronomical Colloquium
Haus der Astronomy, Königstuhl, Auditorium

2014-05-27
17:00
The Peripheries of Galaxies: Dim but not Dull
Annette Ferguson (Univ. Edinburgh)
Heidelberg Joint Astronomical Colloquium
Haus der Astronomy, Königstuhl, Auditorium
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Abstract
Evidence is mounting for the presence of complex low surface brightness structures in the outer regions of galaxies. While the most spectacular examples are provided by systems hosting coherent debris streams, the most common examples may be extremely diffuse stellar envelopes. Wide-field imagers on large telescopes are allowing us to quantitatively explore the resolved stellar populations in these components within and well beyond the Local Group. I will highlight some recent results from our work and discuss the insight these outer structures provide on understanding massive galaxy assembly. I will also discuss how we are using deep HST studies of M31's outer regions to probe its evolutionary history in unprecedented detail.

2014-05-20
17:00
Astronomical probes of fundamental constants
Paolo Molaro (Obs. Astron. Trieste)
Heidelberg Joint Astronomical Colloquium
Haus der Astronomy, Königstuhl, Auditorium
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Abstract
Do the fundamental constants of nature vary over cosmological time and/or distance scales? This question goes into the heart of both cosmology and particle physics since several theories beyond the Standard Model or a quintessence dark energy allow for varying of physical constants. Absorption lines recorded by intervening galaxies in the spectra of distant QSOs are "barcodes" of atomic structures and can probe the variability of constants such as the fine structure constant and the proton-to-electron mass ratio. The current observational claims of a spatial dipole will be critically reviewed and the first results of the ESO Large Program presented. In particular, we will discuss the efforts to reveal possible systematic in the wavelength calibration of the most used spectrographs. The status of the ESPRESSO project for the incoherent combined focus of the VLT will be also briefly described.

2014-05-16
17:00
Ice Cube and the Discovery of High-Energy Cosmic Neutrinos
Francis Halzen (Univ. Wisconsin)
Heidelberg Joint Astronomical Colloquium
INF 227, Otto Haxel Saal
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Abstract
NOTE: This is a joint colloquium between the "Physikalisches Kolloquium" and the "Heidelberg Joint Astronomy Colloquium" and it takes place on Friday in the INF 227

2014-05-06
17:00
Solar System formation and evolution
Alessandro Morbidelli (Observatory of Nice)
Heidelberg Joint Astronomical Colloquium
Haus der Astronomy, Königstuhl, Auditorium
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Abstract
The discovery of over 1,000 extrasolar planets reveals a huge diversity of planetary system architectures, even when restricting the sample to the sole giant planets. We see many Jovian planets at distances from the parent stars comparable to those of our terrestrial planets or even much smaller (hot Jupiters), as well as on orbits with a variety of eccentricities, ranging up to almost unity. These wild and surprising orbits are usually explained invoking two processes: planet migration and planet instabilities. Then, the question arises on whether our Solar System experienced these processes as well and why its structure looks so different from those of the giant planet extrasolar systems discovered so far. Luckily, we have a huge number of observational constraints that can guide us to reconstruct with some confidence the evolution of the Solar System back to the time of giant planet formation. A non-exhaustive list of constraints is made of: the orbits of the giant planets (non-resonant, partially eccentric and inclined), the Earth/Mars dichotomy (mass ratio, formation timescales), the asteroid belt (depleted, excited, featuring 2 distinct populations partially mixed, accretion within 3My, less than 10Gy-equivalent collisional evolution), Jupiter’s Trojans (extremely strong dynamical excitation, L4/L5 asymmetry), the irregular satellites populations (similar for all giant planets once rescaled to the planet’s Hill radius), the Kuiper belt (complex structure with cold, hot, resonant and scattered populations), the Oort cloud (its large population, compared to the Kuiper belt), the Late Heavy Bombardment of the Moon. I will present a model that can explain the global structure of the Solar System, consistent with all constraints listed above. If this model is correct, it suggests that the specific structure of the Solar System is due to some specific and fortuitous events that happened during its evolution. Changing slightly these events produces, through a chaotic propagation of effects, radically different final systems which cover a wide portion of the observed diversity of planetary systems.

2014-04-29
17:00
Transition: When protoplanetary disks reveal their planetary system
Carsten Dominik (University of Amsterdam)
Heidelberg Joint Astronomical Colloquium
Haus der Astronomie, Auditorium
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Abstract
Protoplanetary disks are the cradles of planetary systems. I will discuss new insights that have come together through observations and modeling of disks around Herbig Ae stars, which are nearby young stars surrounded by protoplanetary disks. Recently we have learned that a subclass of these objects, earlier thought to be the less evolved group, all seem to be transitional disks characterised by large gaps and possibly in the process of shedding the disk and revealing the embedded planetary systems. I will discuss both recent observations and modelling efforts to trace the processes in these disks and to try to retrieve information about embedded (proto) planets by looking gap sizes, shapes, and separation of different grains sizes.

2014-04-22
17:00
From classical celestial mechanics to modern stellar dynamics in Astronomy
Roberto Capuzzo Dolcetta (Dep. of Physics, Sapienza, Univ. Rome)
Heidelberg Joint Astronomical Colloquium
Haus der Astronomie, Auditorium
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Abstract
Gravitation is the pervasive engine of astronomical phenomena over all the space scales. The newtonian, classic, gravitational N-body problem is one of the archetipes of complex problems in Physics and has many applications in Astrophysics, from the study of planetary motion to the dynamics of stellar clusters and galaxies up to galaxy clusters. This problem has been studied under both theoretical and numerical points of view and the development of modern software and hardware is nowadays opening new horizons in the understanding of many observed features of the local and far Universe. In this Colloquium I will briefly resume some of the basics of this topic and present an update on recent applications and results, especially of the dynamics of very crowded regions around the massive and super massive black holes in galactic centers.

2014-02-04
17:15
New Insights into The Virgo Cluster
Laura Ferrarese (NRC Herzberg Institute of Astrophysics, Canada)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
At a distance of 16.5 Mpc and with a gravitating mass of 4.2×10^14 solar masses, the Virgo Cluster is the dominant mass concentration in the local universe, the centre of the Local Supercluster, and the largest concentration of galaxies within ~35 Mpc. With thousands of member galaxies lying at a nearly common distance and spanning virtually all known morphological types, it has historically played a key role in studies of how galaxies form and evolve in dense environments. It is, without question, the most thoroughly studied cluster of galaxies in the universe, and remains a preferred target for a systematic survey of baryonic substructures in the low-redshift universe. In this talk, I will present results from the Next Generation Virgo Cluster Survey (NGVS), an ambitious optical imaging survey of the Virgo cluster carried out using the MegaPrime instrument at the Canada France Hawaii Telescope (CFHT), and supplemented with spectroscopic data from Keck, Gemini, MMT, VLT and AAT. Specifically, I will focus on 1) the use of globular clusters as baryonic tracers of the cluster potential; 2) the structure of galaxies and their dark matter content; and 3) the faint end of the galaxy luminosity function and the occupation fraction of low-mass dark matter haloes. Some details about the NGVS can be gathered from the survey webpage: https://www.astrosci.ca/NGVS/The_Next_Generation_Virgo_Cluster_Survey/Home.html

2014-01-28
17:15
Star formation in the Magellanic clouds as seen by low mass stars
Guido De Marchi (European Space Agency, Noordwijk, Netherlands)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
We have undertaken a systematic study of pre-main-sequence (PMS) stars spanning a wide range of masses (0.5 - 4 Msun), metallicities (0.1 - 1 Zsun) and ages (0.5 - 30 Myr). We have used the Hubble Space Telescope to identify and characterise a large sample of PMS objects in several star forming regions in the Magellanic Clouds, namely 30 Dor, the SN1987A field and NGC1850 in the LMC and NGC 346 and NGC 602 in the SMC, and have compared them to PMS stars in similar regions in the Milky Way, such as NGC 3603 and Trumpler 14. Thanks to a novel method that we have developed to combine broad-band (V,I) photometry with narrow-band Halpha imaging, we have determined the physical parameters (temperature, luminosity, age, mass and mass accretion rate) of more than 3000 bona-fide PMS stars still undergoing active mass accretion. This is presently the largest and most homogeneous sample of PMS objects with known physical properties and it includes not only very young objects, but also PMS stars older than 10-20 Myr that are approaching the main sequence. I will present the main results of this research, including the fact that the mass accretion rate scales roughly with the inverse of the cube root of the metallicity and is therefore systematically higher in the Magellanic Clouds than in the Milky Way for stars of the same mass and age. These results are bound to have important implications for, and constraints on our understanding of the star formation process.

2014-01-21
17:15
Supernova remnants colliding with molecular clouds: From TeV to meV emission
Thierry Montmerle (Institut d'Astrophysique de Paris, France)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
It is now well established that a class of gamma-ray sources in the galactic plane, especially in the TeV range as seen by HESS and other Cerenkov telescopes, and in the GeV range by the Fermi and AGILE satellites, is associated with intermediate-age supernova remnants interacting with molecular clouds in massive star-forming regions. After a brief general introduction linking high-energy gamma-rays and the origin of cosmic rays, I will focus on a few such gamma-ray sources (W28, W44, and W51) and the challenging conclusions that can be drawn from them. I will then describe our recent work on related submm measurements and consequences of enhanced ionizing effects in molecular clouds due to locally accelerated low-energy cosmic rays. I will also mention briefly some implications for the "cradle of the Sun" and for the high-energy evolution of OB associations. Work done in collaboration with Cecilia Ceccarelli, Guillaume Dubus, Pierre Hily-Brant, and Solenn Vaupré (Institut de Planétologie et d’Astrophysique de Grenoble, France)

2014-01-14
17:15
Testing the Theory of the Early Universe using the Cosmic Microwave Background
Eiichiro Komatsu (Max-Planck-Institut für Astrophysik, Garching, Germany)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
The Cosmic Microwave Background (CMB), the fossil light of the Big Bang, is the oldest light that one can ever hope to observe in our Universe. The CMB provides us with a direct image of the Universe when it was still an "infant" - 380,000 years old - and has enabled us to obtain a wealth of cosmological information, such as the composition, age, geometry, and history of the Universe. Yet, can we go further and learn about the primordial universe, when it was much younger than 380,000 years old, perhaps as young as a tiny fraction of a second? If so, this gives us a hope to test competing theories about the origin of the Universe at ultra high energies. In this talk I present the final results from nine years of observations using the Wilkinson Microwave Anisotropy Probe (WMAP) satellite, and discuss future prospects on our quest to probe the physical condition of the very early Universe.

2014-01-07
17:15
What can we learn from the observations of gravitational waves?
Hyung Mok Lee (Seoul National University, Republic of Korea)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal

2013-12-17
17:15
The formation and evolution of massive star forming disks
Reinhard Genzel (Max-Planck-Institut für extraterrestrische Physik, München, Germany)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal

2013-12-10
17:15
Booms, Burps & Bumps: The Dynamic Universe
Shri Kulkarni (California Institute of Technology, Pasadena, USA)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
That occasionally new sources ("Stella Nova") would pop up in the heavens was noted more than a thousand years ago. The earnest study of cosmic explosions began in earnest less than a hundred years ago. Over time astronomers have come to appreciate the central role of supernovae in synthesizing new elements (and making life as we know possible). The Palomar Transient Factory (PTF), an innovative 2-telescope system, was designed to explicitly to chart the transient sky with a particular focus on events which lie in the nova-supernova gap. PTF can find an extragalactic transient every 20 minutes and a Galactic (strong) variable every 10 minutes. The results so far: classification of 2000 supernovae, identification of an emerging class of ultra-luminous supernovae, the earliest discovery of a Ia supernovae, discovery of luminous red novae, the most comprehensive UV spectroscopy of Ia supernovae, discovery low energy budget supernovae, clarification of sub-classes of core collapse and thermo-nuclear explosions, mapping of the systematics of core collapse supernovae, identification of a trove of eclipsing binaries and the curious AM CVns.

2013-12-03
17:15
The gas content of galaxies at z<0.2
Jarle Brinchmann (Leiden Observatory, Netherlands)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal

2013-11-26
17:15
Precision Cosmic Ray Physics with AMS on the International Space Station
Roberto Battiston (Trento University, Italy)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
Two years after the launch and begin of operation of AMS on the ISS, precision measurements of cosmic rays composition and spectra are presented. We will discuss the implications of these results on issues ranging from the physics of dark-matter to the physics of cosmic ray composition and acceleration mechanisms as well as the future perspectives.

2013-11-19
17:15
The growth of massive black holes
Marta Volonteri (Institut d'Astrophysique de Paris, France)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
Massive black holes, weighing millions to billions of solar masses, inhabit the centers of today's galaxies. The progenitors of these black holes powered luminous quasars within the first billion years of the Universe. The first massive black holes must therefore have formed around the time the first stars and galaxies formed and then evolved along with their hosts for the past thirteen billion years. I will discuss some aspects of the cosmic evolution of massive black holes, from their formation to their growth and the interplay between black holes and galaxies.

2013-11-12
17:15
The vast polar structures around the Milky Way and Andromeda, and the implications thereof for fundamental physics
Pavel Kroupa (Universität Bonn, Germany)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
The Milky Way has been found to have a rotating vast polar disk-like structure of radius larger than 200kpc and half thickness of about 15 kpc. Andromeda, too, harbors a disk of satellite galaxies, which is, however, even thinner. It is also rotating. The only reasonable explanation for these structures is for them to have formed from tidal material expelled when the Milky Way and Andromeda interacted about 10Gyr ago, either with each other or with other galaxies. The implications of this for gravitational physics would be profound, because the high dynamical M/L ratios of the satellite galaxies in the structures could not stem from dark matter.

2013-11-05
17:15
The Fast Track to Finding an Inhabited Exoplanet
David Charbonneau (Harvard-Smithsonian Center for Astrophysics, Cambridge, USA)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
The investigation of planets orbiting other stars has moved from the study of gas giants to the hunt for smaller planets that are predominantly rock and ice in composition. When such planets are discovered in edge-on orbits, such that the planet and star undergo mutual eclipses, we are granted the opportunity to determine directly the planetary masses and sizes. Most interestingly, we can study starlight filtered through the planetary atmosphere to deduce its chemical composition, and perhaps even search for biosignatures. I will summarize the most recent results from the NASA Kepler Mission and describe two surveys intended to find the closest habitable exoplanet.

2013-10-29
17:15
The Inner Lives of Stars: Asteroseismology, Stellar Physics, and Stellar Populations
Marc Pinsonneault (Ohio State University, Columbus, USA)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal
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Abstract
We are entering a new era of precision stellar astrophysics. Large surveys and upcoming missions, such as Gaia, promise a wealth of high-quality observational data. Asteroseismology is now possible for bulk stellar populations, as demonstrated by both the Kepler and CoRoT missions. I review the basic properties of asteroseismology, focusing on two distinct classes of results: Planet and stellar population studies will benefit enormously from inferences about basic stellar properties (such as mass, radius, and age) from the non-radial frequency patterns in stars, and this data will permit a fundamental calibration of stellar models in the mass plane. A detailed study of the oscillation frequencies also permits stringent tests of stellar physics, and I will demonstrate how important internal features (such as core mass, density, and rotation) are now observables. I finish with an overview of the broad range of applications of precision stellar astrophysics.

2013-10-22
17:15
Cosmology as a laboratory for neutrino physics
Steen Hannestad (Aarhus University, Denmark)
Heidelberg Joint Astronomical Colloquium
Philosophenweg 12, großer Hörsaal

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