0 Assigned ID: 2531 ----- Attempting Submission 1 (Sat Apr 10 01:57:00 GMT 2021) ----- HST Phase I Proposal 2531 successfully submitted. Receipt: # 2531-1 ----- Attempting Submission 2 (Sat Apr 10 02:06:47 GMT 2021) ----- The value of precision in unlocking new science has been repeatedly demonstrated across multiple fields of astrophysics (e.g., CMB cosmology and Milky Way dynamics with Gaia). Stellar photometry with the Hubble Space Telescope (HST) has progressed to the point that a similar push towards precision would reap immediate scientific benefits. Detailed and thorough characterization of HST's optical performance has resulted in unparalleled PSF photometry, but residual systematic errors currently form a barrier in achievable precision. Time-dependent changes to the telescope focus and visible sky background conspire to limit photometric precision to the ~5% level. This barrier currently prevents time-critical science including high-resolution dust mapping in nearby galaxies, and red giant branch distance measurements which are urgently needed to shed independent light on the uncomfortable tension between Cepheid- and CMB-based estimates of the local Hubble parameter. We propose to remove this barrier by deriving corrections at the level of cataloged HST photometry, using machine learning techniques. Specifically, we will leverage archival wide-area multiwavelength data, including the PHAT survey, to model photometric biases induced by variations in the HST PSF, sky background, and other hidden effects. This model will correct resolved stellar photometry as a function of detector position, exposure date, and other telescope parameters. This methodology will be broadly applicable to photometry and cross-calibration of all existing and future space-based stellar catalogs, including HST and Roman, and will allow a new generation of critical precision stellar population studies. PI Durbin is a former WFC3 team member with significant experience in WFC3/IR data analysis and HST photometry generally, and has led several HST photometry studies. Co-I Dalcanton is the of the PHAT survey and has decades of experience with space-based photometry, as well as project management, and is the thesis advisor to PI Durbin. Co-I Williams has decades of experience with PSF fitting photometry of crowded field HST imaging, including the PHAT and PHATTER surveys. Co-I Beaton is an experienced phtometrist with both ground- and space-based photometry in the OIR, in particular in scientific applications for precision photometry. Co-I Gordon is an expert in Gaussian processes and the lead developer of one of the codes we will use in our analysis. Co-I Smercina is experienced in the analysis and interpretation of resolved stellar population observations with HST and ground-based telescopes, and is a member of the PHAT and PHATTER survey teams. Stellar Populations and the Interstellar Medium Stellar Physics and Stellar Types 0 Regular false false false false false SUPPORTED