Spectroscopic Analyses of Helium-rich Subdwarf B Stars

摘要

Helium-rich subdwarf B (He-sdB) stars form a very small fractionof all hot subdwarfs. They have been found both in the field of our galaxy as wellas in globular clusters. The evolution of these rare stars has recently been thesubject of much debate involving both binary and single star evolution models.We present new measurements of the atmospheric parameters of several He-sdBstars which demonstrate that they form a very inhomogeneous group. In partic-ular, we discuss the discovery that PG 1544+488 is a short-period spectroscopicbinary containing two helium-rich subdwarfs. We also discuss the contradiction between FUSE and optical measurements of He-sdB surface gravities and theimplications of these observations for the evolutionary status of He-sdB stars arealso explored.