Stellar population modeling including BSS

Licai Deng (National Astronomical Observatory, China)

 
Observations show that nearly all star clusters and stellar populations contain blue straggler stars (BSS). 
BSS in resolved stellar populations, such as star clusters, can significantly enhance the integrated spectrum 
of the host population, preferentially at short wavelengths, and render it much bluer in photometric colors 
than current evolutionary simple stellar population (SSP) models. The current theoretical SSP models 
constructed within the traditional framework of single and binary stellar evolution cannot fully account for the 
impact of these objects on the integrated spectral properties of stellar populations. Using conventional SSP 
models without taking into account BSS contributions may significantly underestimate a cluster's age and/or 
metallicity, simply because one has to balance the observed bluer colours (or a bluer spectrum) with a 
younger age and/or a lower metallicity. Therefore, inclusion of BSS contributions in SSP models is an 
important and necessary improvement for population synthesis and its applications. In this talk, we present a 
new set of SSP models, which include BSS contributions based on our analysis of individual star clusters. 
The models cover the wavelength range from 91 Å to 160 µm, ages from 0.1 to 20 Gyr and metallicities Z= 
0.0004, 0.004, 0.008, 0.02 (solar) and 0.05. We use the observed integrated spectra of several Magellanic 
Cloud star clusters to cross-check and validate our models.