Blue Straggler Stars in Galactic Open Clusters and the effect of field star contamination

TL;DR

This study examines Blue Straggler stars in open clusters, emphasizing the impact of field star contamination on their observed distribution and the importance of membership analysis for accurate interpretation.

Contribution

It highlights the significant contamination of Blue Straggler counts by young field stars and underscores the need for detailed membership analysis in cluster studies.

Findings

Many Blue Straggler candidates are actually young field stars.

Field star contamination affects the interpretation of Blue Straggler populations.

Blue plumes can serve as tracers of Galactic structure.

Abstract

We investigate the distribution of Blue Straggler stars in the field of three open star clusters. The main purpose is to highlight the crucial role played by general Galactic disk fore-/back-ground field stars, which are often located in the same region of the Color Magnitude Diagram as Blue Straggler stars. We analyze photometry taken from the literature of 3 open clusters of intermediate/old age rich in Blue Straggler stars, and which are projected in the direction of the Perseus arm, and study their spatial distribution and the Color Magnitude Diagram. As expected, we find that a large portion of the Blue Straggler population in these clusters are simply young field stars belonging to the spiral arm. This result has important consequences on the theories of the formation and statistics of Blue Straggler stars in different population environments: open clusters, globular clusters or dwarf galaxies. As previously emphasized by many authors, a detailed membership analysis is mandatory before comparing the Blue Straggler population in star clusters against theoretical models. Moreover, these sequences of young field stars (blue plumes) are potentially powerful tracers of Galactic structure which require further consideration.