The Spectral Evolution of Young Starbursts: the Effects of Massive Binaries

We present part of the results of our extensive investigation on the influence of massive binaries on the spectral properties of young star-forming regions. We focus on the optical region, containing the so-called blue and red Wolf-Rayet bumps at 4650Å and 5810Å, as well as on the hard X-ray region (E > 2 keV), which is dominated by the contribution of high mass X-ray binaries (HMXBs) and young supernova remnants (YSNRs). It is found that the inclusion of massive binaries is necessary to correctly interpret the observations of unresolved starburst regions. The comparison between our theoretical predictions and the observations of the Wolf-Rayet bumps of starbursts at low metallicity indicate that the Wolf-Rayet mass-loss rates are metallicity dependent. The hard X-ray spectrum of a starburst is dominated by wind-fed HMXBs, while the contribution from YSNRs depends sensitively on their initial pulsar spin period, which is as yet undetermined. A more detailed description of the results presented here can be found in van Bever & Vanbeveren (2000, 2003) and van Bever (2004).