Simple stellar population models including blue stragglers

Abstract

Observations show that nearly all star clusters and stellar populations contain blue straggler stars (BSs). BSs in a cluster can significantly enhance the integrated spectrum of the host population, preferentially at short wavelengths, and render it much bluer in photometric colours. Current theoretical simple stellar population (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 BS 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 BS contributions in SSP models is an important and necessary improvement for population synthesis and its applications. Here, we present a new set of SSP models, which include BS contributions based on our analysis of individual star clusters. The models cover the wavelength range from 91~{\AA} to 160~$\mu$m, 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. The results show that the age predictions from our models are closer to those from isochrone fitting in the clusters' colour-magnitude diagrams compared to age predictions based on standard SSP models.Comment: 16 pages, 15 figures, 4 tables, accepted for publication in MNRA

Systematic differences in simple stellar population model results: application to the M31 globular-like cluster system

“…Fan et al , ; Ma et al , ; Wang et al ). In this paper, we take the advantage of the availability of a new set of SSP models that attempt to correct for the contributions of BSs (Xin et al ). The BS‐SSP model suite is based on the Padova 1994 isochrones and the BaSeL–Kurucz stellar spectral library.…”

“…Consequently, stellar population synthesis has become an important and powerful tool to interpret the nature of extragalactic star clusters, including their ages, metallicities, reddening values and masses. In the past few decades, many different simple stellar population (SSP) synthesis models have been constructed and applied to study extragalactic star clusters based on photometry in multiple passbands, including Bruzual & Charlot (, ), Worthey (), Leitherer & Heckman (), Fioc & Rocca‐Volmerange (), Maraston (, ), Vazdekis (), Yi et al (), Conroy et al (), Xin et al (), as well as the GALEV models (see e.g. Schulz et al ; Anders & Fritze‐v.…”

“…Alvensleben & Bicker ; Kotulla et al ). The recently updated BS‐SSP models (Xin et al ) considered the effects of blue straggler stars (BSs), which are likely the products of binary mergers and which seem to have a common occurrence in star clusters (see e.g. Ahumada & Lapasset ; Piotto et al ; Xin et al ).…”

“…The recently updated BS‐SSP models (Xin et al ) considered the effects of blue straggler stars (BSs), which are likely the products of binary mergers and which seem to have a common occurrence in star clusters (see e.g. Ahumada & Lapasset ; Piotto et al ; Xin et al ). Since BSs are often luminous and can render the integrated luminosities and colours of their host clusters significantly brighter and bluer, we set out to explore the differences between results derived from the application of the BS‐SSP models and those derived from other models.…”

A VIMOS spectroscopy study of photometric variables and straggler candidates inω Centauri

“…Most probably, they are evolutionary advanced blue stragglers (e.g. Xin et al 2011), and distinguishing between these two groups of objects seems to be a matter of taste rather than physical necessity. Red stragglers are found to the right of the main sequence, below the subgiant branch.…”