Abstract

Contributed Talk - Splinter CloseBinaries   (MW-0250)

Hot subdwarf stars from the Hamburg Quasar Survey: Evidence for the merger origin of helium-rich subdwarfs

L. Kufleitner (1), U. Heber (1), M. Dorsch (2), M. Latour (3), H. Dawson (2), F. Mattig (2) and S. Geier (2)
(1) FAU Erlangen-Nürnberg, (2) Uni Potsdam, (3) Uni Göttingen

Hot subdwarf stars (sdO/B) are evolved low-mass stars formed from red giants that have lost nearly all of their envelopes, likely through multiple evolutionary channels involving close binary interactions. Using improved hybrid LTE/non-LTE model atmospheres and Gaia astrometry, we present a spectroscopic analysis of 122 non-composite subdwarfs discovered in the Hamburg Quasar Survey. We confirm that sdB stars reside on the extreme horizontal branch with a canonical mean mass of 0.45 M_Sun and find no significant differences in the mass distributions of pulsating and non-pulsating sdBs. In contrast, the helium-rich sdOB and sdO stars are located near the helium main sequence and exhibit a mass distribution peaking at higher masses. Their locations in the Hertzsprung–Russell diagram and their masses support a formation scenario where these stars are the products of helium white dwarf mergers, establishing the helium-rich subdwarfs as the evolutionary descendants of compact double white dwarf binaries.