Census of Blue Straggler Stars in Distant Open Clusters and Maximum Fractional Mass Excess of Open Cluster Blue Straggler Stars

Abstract

We identified blue straggler stars (BSSs) in 53 open clusters utilizing data from Gaia DR3. Most of these clusters are situated in the outer regions of the Galactic disk, encompassing structures such as the warp and the Outer arm. We analyzed their astrometric parameters and determined that 48 of them demonstrate high reliability in the radial density profile. Furthermore, through manual isochrone fitting and visual inspection, we confirmed 119 BSS candidates and identified 328 additional possible candidates within these clusters. Our results contribute to a 46% increase in the sample size of BSSs in open clusters for regions of the Galactic disk where R _gc > 12 kpc. We observed that the new samples are fainter compared to those identified in the past. Additionally, we investigated the maximum fractional mass excess ( M _e ) of the BSSs in open clusters, including previously published BSS samples. Our findings indicate a strong correlation between the capability to produce highest- M _e BSSs and the mass of their host clusters. This observation appears to reinforce a fundamental principle whereby an increase in the mass of a star cluster correlates with a higher likelihood of stellar mergers. In contrast, we observe minimal correlation between maximum- M _e and the cluster age. Among clusters containing BSSs, younger clusters (0.5–1 Gyr) display a scarcity of high- M _e BSSs. This scarcity may be attributed to the absence of more massive clusters within this age range.

Keywords

• Blue straggler stars
• Open star clusters