Modeling blue stragglers in young clusters

TL;DR

This paper models blue straggler formation in young star clusters through binary evolution, analyzing different formation channels and comparing simulated populations with observations to understand their properties.

Contribution

It provides a systematic study of blue straggler formation via mass transfer and merging using a grid of binary evolution models, including effects of mass transfer efficiency.

Findings

BSs from Case B are bluer and more luminous than from Case A.

Case B models produce more BSs due to larger orbital separation range.

Different formation channels occupy distinct regions in the color-magnitude diagram.

Abstract

In this paper, a grid of the binary evolution models are calculated for the study of blue straggler (BS) population in intermediate age ($\log Age$=7.85-8.95) star clusters. The BS formation via mass transfer and merging is studied systematically using our models. Both Case A and B close binary evolutionary tracks are calculated in a large range of parameters. The results show that BSs formed via Case B are generally bluer and even more luminous than those produced by Case A. Furthermore, the larger range in orbital separations of Case B models provide a probability of producing more BSs than Case A. Based on the grid of models, several Monte-Carlo simulations of BS populations in the clusters in the age range are carried out. The results show that BSs formed via different channels populate different areas in color magnitude diagram(CMD). The locations of BSs in CMD for a number of clusters are compared to our simulations as well. In order to investigate the influence of mass transfer efficiency in the models and simulations, a set of models are also calculated by implementing a constant mass transfer efficiency, $\beta$=0.5 during Roche lobe overflow (Case A binary evolution excluded). The result shows BSs can be formed via mass transfer at any given age in both cases. However, the distributions of the BS populations on CMD are different.