Vorträge, Seminare, Ereignisse

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Black holes power many of the most powerful sources in the universe through their disks, jets and winds. This power derives from their rotational energy (Nature) and the gravitational energy released by accreting gas (Nurture). The balance of these two modes and their implications, will be re-examined in the light of recent, remarkable observations of the nearby galaxy M87 by the Event Horizon Telescope. Implications for other sources will be discussed. Professor Blandford is hosted by Dr. Brian Reville (brian.reville@mpi-hd.mpg.de)

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Massive stars play a dominant role in the energetics of their host galaxies, primarily by their radiation-driven winds enriching their local stellar environments and by ionizing radiation. A subset of the massive stars, the Wolf-Rayet stars, which are direct progenitors of stellar-mass black holes, have particularly strong stellar winds. These winds are so powerful that they effectively push away the outer layers of the Wolf-Rayet star, obscuring it from sight. Hence, only the stellar wind can be observed from Earth. To infer stellar parameters, one needs to rely on a proper modelling of the winds of these stars. In this talk, I will show the deficiencies of the current wind modelling for Wolf-Rayet stars along with accompanying uncertainties on stellar parameters with solutions to construct more accurate models.

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Since the discovery of the first extrasolar planet orbiting a Sun-like star in 1995, exoplanet science has been evolving into a highly dynamic field of modern astrophysics. Today, almost 5000 exoplanets have been confirmed and, thanks to ongoing efforts from the ground and from space, this number keeps continuously increasing. Most of the planets have been discovered via indirect techniques, such as the radial velocity and transit techniques. However, the direct detection of exoplanets is required to significantly expand the exoplanet discovery space, provide crucial links to planet formation studies, and, ultimately, test hypotheses related to exoplanet habitability and the possible existence of atmospheric biosignatures in a statistically relevant sample of objects. I will briefly discuss the challenges that need to be overcome to take a direct image or a spectrum of an exoplanet and then describe a roadmap what we can expect to learn from the direct detection of exoplanets as we go from currently available observatories (e.g., VLT and, very soon, the James Webb Space Telescope), to future observations with the ELT and, eventually, to new flagship-class space missions.

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Our understanding of the formation and evolution of the Milky Way is often blurred and biased by the lack of precise and accurate stellar ages. In this contribution I will present the ongoing efforts and recent results of the asterochronometry project (https://asterochronometry.eu/ [asterochronometry.eu]), which aims both at testing and improving our knowledge of stellar physics, and at determining precise and accurate ages of stars (to 10-15%) in the regions of the Galaxy sampled by Kepler, K2, CoRoT, and TESS. Examples of recent and ongoing work will include age-dating stars using data from the TESS mission and inferences on the ages of both Gaia-Enceladus and in-situ stars observed by Kepler. Finally, I will discuss the prospects for extending these studies to larger samples, and briefly present the science case for a future mission dedicated to asteroseismology of crowded fields. Prof. Miglio is hosted by Hans-Guenther Ludwig (hludwig@lsw.uni-heidelberg.de). zoom access code 69120

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The highly praised ESA Gaia satellite mission has already provided the astronomic communitywith high quality astrometric, photometric and other data for almost 2 billion stars, and will continue to do sofor the next years. As time goes by, the precision of the astrometry increases with the number of measurementsand the time-span during which these are obtained, growing. Thus the correction of systematic effects in thedata, such as aberration need to be corrected to a point, where the conventional means do not suffice anymore.To accomplish this, a programme was conceived, to track the satellite with highly precise (20 mas) groundbased astrometry to deliver the required data for the optimisation of Gaia’s accuracy, called Ground BasedOptical Tracking (GBOT). This programme has faced many challenges and uncertainties, as well as set backs,but finally GBOT has come to the point, where its data are being included in the processing of the Gaiaastrometry, since 2020.This presentation will give an overview of the history of GBOT, and the steps taken to ensure final success,after many years of challenges. I will also report on a project searching for asteroids on the existing GBOTdata, which has lead to observations of about 42,000 objects, of which about 18,000 were previously unknown.

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Gas and dust in inclined orbits around binaries experience precession induced by the binary gravitational torque. The difference in precession between gas and dust alters the radial drift of weakly coupled dust and leads to the formation of dust traffic jams where the radial drift is minimised. I explore this new phenomenon using 3D SPH simulations and investigate its dependence on disc initial inclination and binary eccentricity. I will then present a new dust evolution model that takes the mutual gas and dust inclination into account and reproduce the SPH results, which provides a straightforward way to understanding dust traffic jams as a consequence of the drag torque exerted by the gas on the dust. Finally, I will present the results of radiative transfer post-processing of the hydro simulations and discuss possible observational implications of these dust traffic jams.

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The processes of star formation and feedback take place on the cloud scale (~100pc) within galaxies and play a major role in governing galaxy evolution. The properties of the clouds in which stars form are set by the large scale environment of their host galaxies, directly linking the initial conditions of star formation to galactic-scale properties. In turn, the energy, momentum,and mass deposited by stellar feedback drive the continuous evolution of the interstellar medium at large. Characterising the physical mechanisms regulating this multi-scale cycle is therefore crucial to understand the evolution of galaxies. By applying a new statistical method to the high-resolution CO and narrowband-Halpha imaging from the PHANGS survey, we systematically measure the evolutionary timeline from molecular clouds to exposed young stellar regions on the scales of giant molecular clouds across an unprecedented sample of 54 main sequence galaxies. We find that clouds live for about one dynamical time (8-30 Myr) and are efficiently dispersed by stellar feedback within 1.2-5.1 Myr after the star-forming region has become partially exposed. These ranges do not indicate uncertainties, but reflect physical galaxy-to-galaxy variation, implying an important dependence of these timescales on the local conditions, shaped by the galactic environment. The statistically representative PHANGS sample covers a large range of galaxy properties and morphologies, which allows us, for the first time, to quantitatively link galactic-scale environmental properties to the small-scale evolutionary cycle of molecular clouds, star-formation, and feedback. I will present the first census of these multi-scale trends. These results enable the characterisation of the physical mechanisms regulating cloud assembly, star formation, and cloud disruption, which eventually participate in driving galaxy evolution, as a function of the galactic environment.

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High-mass stars are very important to many areas of Astronomy. These objects deeply impact their surroundings through their powerful winds and their deaths as supernovae. Therefore,understanding the behavior of such stars is essential to understand their impacts on their hostgalaxies' properties and history.The aim of this research project is to analyze the atmospheres of B supergiants (BSGs, evolvedmassive stars) using the CMFGEN (Hillier & Miller 1998), a 1D, non-LTE atmosphere code — which is one of the state-of-the art tools used to analyze hot stars. The focus of the project is to investigate whether more recent models (e.g., the inclusion of x-rays, clumping, more recent atomic data) can better explain the optical and UV observed spectra of these stars, since previous studies failed to model several important UV lines (Crowther et al. 2006; Searle et al. 2008).As results we obtained (i) an overall improved agreement between BSGs observed and model spectra at the UV considering the effects of clumping and x-rays in the wind. Also we noticed (ii)important differences in their properties between hot (B1 – B0) and warm (B2 - B5) BSGs were also found, and it is in agreement with recent hydrodynamical simulations, such as Driessen et al.(2019). Beyond that, (iii), we have found a general trend of the CNO abundances for BSGs compatible with previous works in the literature and to the current high-mass stellar evolutionpredictions. However, (iv) despite a decrease in terminal velocity at the Bi-Stability Jump, we found no increase in mass-loss, instead, we have found a slightly decreasing trend towards later spectral types.

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The award winner will present their work.