RESEARCH
The initial mass function (IMF) is important for various fields of astrophysics: it determines
observable properties of stellar systems, the chemical enrichment of the interstellar medium
and supernova rates. Furthermore we can learn much about star formation if we know the
IMF. However, to measure the IMF directly is impossible because we can only observe the
current mass distribution of stars. It is therefore of utmost importance to know systematic
effects which may cause variations in the observed present day mass function (PDMF). In this
work we explore the impact of stellar and binary evolution on the PDMF by means of a rapid
binary evolution code. We find that wind mass loss flattens the PDMF significantly at the
highest masses observed. Mass transfer due to Roche lobe overflow (RLOF), stellar mergers
and the concomitant rejuvenation can shape the PDMF by large amounts. These effects
together with those due to unresolved binaries also flatten the observed mass function and
hence the inferred IMF. Star formation histories with a recent starburst act like an amplifier
for evolutionary effects. If mass transfer is highly conservative the inferred power law index
Γ of the IMF may change by ΔΓ ≈ 1 towards a flatter IMF for masses between ~8 and 30 Msun
and towards a steeper IMF for masses >30 Msun. If we switch the mass transfer efficiency to
a minimum these deviations are still of the order of ΔΓ ≈ 0.2–0.3. We conclude that binary
interactions need to be taken into account to determine the IMF and provide a method to
correct for all mentioned effects.
Find a copy of my thesis here.
Bachelor Thesis
While working on my Bachelor Thesis I studied stellar dynamics in the galactic center. I tried to investigate the so called Kozai resonance
between two objects orbiting a central body. The eccentricity and inclination of the lighter, inner object can change periodically in time under certain
conditions. Since the galactic center has an extremely high density we were concerned about the question whether the Kozai mechanism can actually work in
such a rough environment. The result is that it can indeed be found in such systems, if the perturber mass is of the order of 1000-10000 solar mass (e.g. IMBHs)
and the perturbed stars have orbits similiar to the S-Stars in the galactic center (so very close orbits to the central SMBH: 0.001 < a < 0.01 pc). So one
can speculate that if there exist IMBHs of the mentioned masses in the very center of the Milky Way they will influence the orbits of the S-Stars via Kozai resonances (and may
potentially be responsible for their strange eccentricity- and inclination-distributions).
|