0 Assigned ID: 3141 ----- Attempting Submission 1 (Fri Mar 25 05:13:44 GMT 2022) ----- Although time-domain data from ground-based surveys are abundant, extragalactic variable stars in crowded regions (such as stellar clusters) and in the faint regime, i.e., the lower part of the Hertzsprung-Russell diagram, are beyond the reach of these surveys due to limitations on angular resolution and sensitivity. On these fronts, the Panchromatic Hubble Andromeda Treasury (PHAT) survey of our spiral neighbor M31, with a resolution of a few tens of milli-arcseconds and a depth reaching 27-28 mag, is unrivaled. It has yielded significant scientific products, among others resolved maps of star formation history (SFH), as well as catalogs of stellar clusters in its footprint. Interestingly, the PHAT survey has a time-domain facet on account of its tiling strategy, particularly in the optical filters F814W and F475W, resulting in sparse light curves for stars covering a wide range of baselines from hours to months. These light curves remain largely unexplored. We propose to perform the first systematic studies of (1) faint, i.e., F814W>20, variable stars, and (2) luminous variables in clusters in a Milky Way analog by mining the PHAT dataset. We will derive their variability characteristics (such as amplitude, color variation) and use available information of their local environment (e.g., age of the cluster, SFH map) to constrain their progenitors and confront with theoretical pulsation models. We will perform comparisons between our results and those from the metal-poor Magellanic Clouds, as well as between our cluster variable stars and field variable stars in M31, to constrain the effect of the environment. Dr. Soraisam is an expert on stellar variability and statistical data analysis, who has done extentive study of variable stars, including those in M31. Prof. Guhathakurta is an expert on stellar populations and galaxy structure and dynamics. Dr. Williams is an expert on stellar populations, galaxy formation and evolution, and also HST photometry, who has led the data reduction of the PHAT survey producing the photometry catalogs, which we will use in this program. Dr. Olsen is an expert on stellar populations, galaxy formation and evolution, and also the lead of NOIRlab's Astro Data Lab science platform, which we will be using to perform our data-intensive analysis. Dr. Johnson is an expert on stellar clusters, and led the PHAT study of clusters, which we will use in this program. Dr. Girardi is an expert on theoretical modelling of stars, stellar populations, and galaxy formation and evolution. Mr. Mukherjee is a graduate student and Mr. Patel, an undergraduate student working with Prof. Guhathakurta and Dr. Soraisam. Stellar Physics and Stellar Types 0 Regular false false false false false false SUPPORTED