Spectroscopic Analysis of Eclipsing Hot Subdwarf Binaries
Samaneh Zahmatkeshfilabi, Stephan Geier
Hot subdwarf stars (sdB/O) are located at the end of the blue horizontal branch on the Hertzsprung-Russell Diagram. The majority of the sdB stars are core helium-burning stars, arising from red giants that shed their outer hydrogen layers. Since a high number of those stars are discovered in binary systems, it is believed that this mass loss mechanism can be related to the interaction of components in a binary system such as the unclear common envelope phase. To improve our knowledge of sdB formation and the common envelope phase, we conducted a time-resolved spectroscopic analysis of eclipsing hot subdwarf stars of HW Vir type based on data of the EREBOS (Eclipsing Reflection Effect Binaries from Optical Surveys) project to derive radial velocity curves, atmospheric parameters and companion masses. Based on the atmospheric parameters, we verified that the primary stars in those binaries are mostly sdBs, with only two exceptions that are likely extremely low-mass helium white dwarfs. The companions are either brown dwarfs with masses around 0.08 M⊙ or late M dwarfs in the mass range M = 0.08 – 0.45 M⊙ quite typical for HW Vir type systems.