Spectral synthesis including massive binaries

TL;DR

This paper introduces a new spectral synthesis code that includes massive binaries, showing improved agreement with observations of young stellar populations by accounting for binary effects on spectra and stellar evolution.

Contribution

The paper presents a novel spectral synthesis model incorporating massive binaries, enhancing the accuracy of stellar population predictions compared to single-star models.

Findings

Binary populations are bluer and have fewer red supergiants.

Wolf-Rayet stars occur over a wider age range, increasing UV flux.

Nebular emission significantly affects observed properties.

Abstract

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