The masses of sdB and sdO stars

Abstract

Mass is a fundamental parameter, but the masses are not well known for most hot subdwarfs. We propose a method of determining the masses of hot subdwarfs. Using this method, we studied the masses of hot subdwarfs from the ESO supernova Ia progenitor survey and the Hamburg quasar survey. The study shows that most of the subdwarf B stars have masses between 0.42 and 0.54 M⊙, whilst most sdO stars are in the range 0.40∼0.55 M⊙. Comparing our study to the theoretical mass distributions of Han et al. (Mon. Not. R. Astron. Soc. 341:669, 2003), we found that sdO stars with mass less than ∼0.5 M⊙ may evolve from sdB stars, whilst most high-mass (>0.5 M⊙) sdO stars result from mergers directly.