Accounting for Blue Straggler Stars in Galaxy Age Calculations

Blue Straggler Stars (BSS) are unusually bright, blue, and young-appearing stars that typically form from the merging or collision of two older stars. As such, it is thought that when using simple stellar population (SSP) models to determine the ages of galaxies, the presence of BSS may cause the ages to skew younger than they actually are. In this study, we used Rain's 2021 BSS catalog and Cantat-Gaudin's 2018 stellar catalog to establish some preliminary relationships between the age of a stellar cluster and its BSS to Main Sequence Star (MSS) ratio. We then used these relationships to add in a "ghost population" of BSS to SSP models. We compared the predicted ages of stellar populations for BSS and non-BSS models across a range of absolute magnitudes and BP-RP values. We found that for the same observable values, the models that took BSS into account predicted the ages of the oldest stellar populations to be some 8 billion years older than the non-BSS models predicted. As this difference is quite extreme, the result warrants further investigation into how BSS and their different evolutionary stages skew SSP models.