The stability of late-type stars close to the Eddington limit

Super-Eddington luminosities in hydrostatic model atmospheres manifest themselves by the presence of gas pressure inversions. Such inversions are not an artifact of the assumption of hydrostatic equilibrium but can also be present in hydrodynamical model atmospheres. Only for very large mass loss rates hardly realized in supergiants will the inversions be removed. Instabilities may, however, still be present in such inversions, which is investigated for both H-rich and H-deficient late-type supergiant model atmospheres. A local, non-adiabatic, linear stability analysis reveals that sound waves can be amplified due to the strong radiative forces. However, despite the super-Eddington luminosities, the efficiency of the radiative instabilities is fairly low compared to for early-type stars with growth rates of $10^{-5} s^{-1}$.Comment: 11 pages; accepted for publication in Astronomy & Astrophysic

Stellar abundance analyses in the light of 3D hydrodynamical model atmospheres

I describe recent progress in terms of 3D hydrodynamical model atmospheres and 3D line formation and their applications to stellar abundance analyses of late-type stars. Such 3D studies remove the free parameters inherent in classical 1D investigations (mixing length parameters, macro- and microturbulence) yet are highly successful in reproducing a large arsenal of observational constraints such as detailed line shapes and asymmetries. Their potential for abundance analyses is illustrated by discussing the derived oxygen abundances in the Sun and in metal-poor stars, where they seem to resolve long-standing problems as well as significantly alter the inferred conclusions.Comment: Invited talk at IAU Symposium 210 "Modelling of Stellar Atmospheres", Uppsala, Sweden (12 pages

Understanding the role of faith in decisions to persist in college for first-generation Black male students

While the admissions rate for Black students is now equivalent to that of White students, there is still a large gap in persistence and graduation rates. Among Black students there is a significant graduation rate gap between Black male and female students. The writer used a qualitative research design to make preliminary observations of the decisions to persist in college of a small sample of first-generation African American male students. As students in a Christian university, the dominant role of faith in decisions to persist emerged as an important theme