The origin of subdwarf B stars
Abstract
The origin of subdwarf B stars (sdBs) is unclear. Different formation channels are proposed including: close-binary evolution, helium-mixing on the red giant branch and the hot flasher scenario. Circumstantial evidence exists that sdBs can result from single star evolution in high metallicity populations. We investigate this possibility by using membership in the thin, thick disk and halo populations as a metallicity indicator. Radial velocity measurements were com-bined with Gaia proper motions to calculate space motions in the Galaxy. Galactic orbits and population memberships were derived. Preliminary results indicate more sdBs are members of the thin disk (86 sdBs) than of thick disk and halo (28 sdBs). Apparently single sdBs are found among all three populations. We look into the temperature distributions of the different types and discuss implication for formation scenarios.