2023 109 P

Identifying and Characterizing Red Stragglers and Sub-Subgiants in Globular Clusters using Multiwavelength HST Photometry

By: Cory Hoo

Department: Physics & Astronomy

Faculty Advisor: Dr. Adrienne Cool

Red stragglers and sub-subgiants (SSGs) are stars that cannot be understood in the context of single-star evolution. Many are known to be binary star systems, but their exact origins remain uncertain. Following Geller et al. (2017), we consider SSGs to be fainter than subgiants and redder than the main sequence (MS), and red stragglers to be stars that are redder than red giants but brighter than subgiants. Here we report the preliminary results of an effort to identify and characterize red stragglers and SSGs in globular clusters using the Hubble Space Telescope (HST) UV Globular Cluster Survey (HUGS; Nardiello et al. 2018). Using HUGS photometry in F275W, F336W, and F438W filters as well as F606W and F814W from the earlier ACS Survey of Galactic Globular Clusters, we construct multiple color-magnitude diagrams to explore the behavior of these enigmatic stars over a wide range of wavelengths. The HUGS membership information enables us to select stars that are very likely cluster members, avoiding potential confusion from foreground objects. Additional parameters provided by HUGS further allow us to select stars with the most reliable photometry. This work will enable comparisons of red straggler and SSG populations in globular clusters with a wide variety of properties as represented in the HUGS survey.