Stellar populations in gravitationally bound systems

Tereza Jerabkova
HISKP, University of Bonn

Stars form in dense sub-parsec regions of molecular clouds, while at the same time, star-forming regions are inevitably coupled to the galactic gravitational potential. This talk will address the complex multi-scale physical nature of star-formation by combining a detailed investigation of resolved star-forming regions using Gaia data with theoretical modelling of stellar populations. In particular, the discovery and my confirmation and theoretical explanation of the unexpected existence of three stellar populations in the young Orion Nebula Cluster present a clear example of the importance of pc-scale processes such as stellar dynamics on star and star-cluster formation. Furthermore, I will present the discovery, made possible with the advent of the Gaia space mission, of 100-pc long and few-pc thin co-eval filaments of star formation, a new fact posing novel viable constraints for theories of star-formation. Using these, and previous, constraints on star formation, I build bridges to the galactic scales using the Integrated Galactic Initial Mass Function (IGIMF) theory. The publicly available code, GalIMF, has been co-developed within my doctoral studies to synthesise stellar populations of whole galaxies. This allowed me to compute, for the first time, a large grid of the empirically driven variable galaxy-wide stellar initial mass function for direct comparison with observations. This modelling and the associated code were used, for example, to construct the cosmic star-formation history with a variable stellar-initial mass function. In a nutshell, I aim to present a multi-scale and multi-technique contribution to star-formation and stellar populations opening novel and original routes for future research. [Referees: Prof. Dr. Pavel Kroupa, Prof. Dr. Karl Menten, Prof. Dr. Simon Stellmer, Prof. Dr. Hubert Schorle, Prof. Dr. Andrew Hopkins]

Investigation on gravitational star-disk encounters producing

Master Colloquium
Luis Lauro Aizpuru Vargas
Max-Planck-Institut für Radioastronomie and Forschungszentrum Jülich

The recent discovery of two Inter-Stellar Objects (ISO) in our own Solar System has prompted astronomers to come up with theoretical explanations on how they are produced. Most newly formed stars are initially surrounded by a protoplanetary disks. The main hypothesis is that these ISOs were planetesimals in such disks and that through one mechanism or another became unbounded to their host stellar system. These same stars are preferentially formed in stellar clusters. The gravitational effects that result from the interaction between disks and stars are thus common and relevant for the understanding of the fate of such disks. Amongst these mechanisms there is the gravitational stellar fly-by encounter. The partial destruction of the disk by the perturber star produces a varying number of unbounded planetesimals. Several studies have looked into the effects of stellar fly-bys on disks both for the co-planar prograde case and for inclined retrograde cases. They investigated properties such as final disk size or final fate of the test particles. However, the particles that become unbound have attracted little attention so far. This work focuses on the particles that become unbound during such fly-bys contributing to the ISO population. We perform numerical simulations of a range of parabolic inclined encounters with varying pertuber star masses and periastron distances for the encounters. The parameter space explored in this work is relevant for a typical stellar cluster environment. Here we focus on the relative amount and the velocities of ISOs produced during such a fly-bys. We found that the velocity distribution of unbounded test particles varies according to the different possible combination of parameters. Nonetheless, the velocities were found to be in the range between 0.3 km/s and 3.0 km/s. These results can be applied to cluster simulations as to determine the velocities of ISOs the cluster as a whole produces. Using the results of this particular work along with the available literature on the velocities of ISOs produced by other sources, we can make a quantitative distinction between the different types of ISOs. As a follow up study, more precise cluster simulations accounting for the IMF function and considering binary populations and viscous disks would provide a more realistic and comprehensive study of the production of ISOs in clusters. [Referees: Prof. Susanne Pfalzner, Prof. Pavel Kroupa]