Evolutionary Synthesis Models of Young Star‐forming Regions: The Influence of Binary Stars

Abstract

The effects of massive close binary systems on observable properties of young star-forming regions with an age smaller than ~40 Myr is evaluated using the population synthesis code LavalSB. This code was developed in parallel with Starburst99. Evolutionary tracks for the binary stars included in LavalSB result from an adaptation of the tracks produced by de Loore & Vanbeveren. These tracks have been modified to be consistent with the single-star evolutionary tracks from the Geneva group, which are already included in LavalSB. Models for various stellar populations with different metallicities are presented, using mainly a frequency of massive close binary systems equal to 30% and considering that binary stars with an initial mass larger than 40 M☉ do not undergo a Roche lobe overflow. For stellar populations younger than 5 Myr, we confirm that the effect of binary systems is negligible. For populations older than 5 Myr, the number of O and Wolf-Rayet stars, the high-energy continuum flux, and the energy deposition rate by the stellar winds into the interstellar medium are affected by the presence of binary systems. On the other hand, the strength and shape of the ultraviolet lines, the magnitudes, the colors, the supernova rate, and the mass deposition rate in the interstellar medium are not significantly changed.