Spectral population synthesis including massive binaries

Abstract

We have constructed a new code to produce synthetic spectra of stellar\npopulations that includes massive binaries. We have tested this code against\nthe broadband colours of unresolved young massive stellar clusters in nearby\ngalaxies, the equivalent widths of the Red and Blue Wolf-Rayet bumps in\nstar-forming SDSS galaxies and the UV and optical spectra of the star forming\nregions Tol-A and B in NGC5398. In each case we find a good agreement between\nour models and observations. We find that in general binary populations are\nbluer and have fewer red supergiants, and thus significantly less flux in the\nI-band and at longer wavelengths, than single star populations. Also we find\nthat Wolf-Rayet stars occur over a wider range of ages up to 10^7 years in a\nstellar population including binaries, increasing the UV flux and Wolf-Rayet\nspectral features at later times. In addition we find that nebula emission\ncontributes significantly to these observed properties and must be considered\nwhen comparing stellar models with observations of unresolved stellar\npopulations. We conclude that incorporation of massive stellar binaries can\nimprove the agreement between observations and synthetic spectral synthesis\ncodes, particularly for systems with young stellar populations.\n