WR Populations in Starbursts: WN and WC Subtypes and the Role of Binaries

Abstract

We present the first results of a new set of population synthesis models, which utilize the latest stellar evolutionary tracks, recent non-LTE atmosphere models which include stellar winds, and observed line strengths in WR spectra to predict the relative strengths of various WN and WC/WO emission features in the spectra of starburst galaxies. Our results will be used to derive accurate numbers of WN and WC stars in starburst galaxies. We also analyze the frequency and the WN and WC content of WR-rich galaxies in low metallicity samples; the theoretical predictions are found to be in good agreement with the observed frequencies. We also discuss the possible role of massive close binaries in starburst regions. If the starburst regions are formed in relatively instantaneous bursts we argue that, given their young age as derived from emission lines equivalent widths, (1) in the majority of the observed WR galaxies massive close binaries have not contributed significantly to the WR population, and (2) nebular HeII 4686 emission is very unlikely due to massive X-ray binaries.