Physical Parameters for Subdwarf B Stars with Composite Spectra

Abstract

For many years, the evolutionary origins of subdwarf B stars remained a mystery. Observations of sdB stars with composite spectra and theoretical considerations suggested that binary star evolution should play a major role, but proof that a large fraction are binaries has taken a decade to establish. Whilst many sdB stars have recently been recognised to be in short-period binaries with unseen companions [8], we have focused on sdB stars in which the spectrum of the secondary can be seen [5]. We previously studied these systems by means of their flux distributions [1] and shown that the secondaries are probably main-sequence G stars. This result has been confirmed from analysis of their optical and near-infrared spectra [2].