Assigned ID: 537 ----- Attempting Submission 1 (Fri Feb 24 18:13:11 GMT 2012) ----- HST Phase I Proposal 537 (snr_2012.apt) successfully submitted. ----- Attempting Submission 2 (Sat Feb 25 00:39:38 GMT 2012) ----- One of the key constraints on the production of supernovae (SNe) is the initial mass of the stars that eventually end in these cataclysmic events. Historically it has been very difficult to obtain estimates of the masses of SN progenitors because there have only been a few dozen nearby events, only a handful of which have high-quality precursor imaging. We propose dramatically increasing the number of SNe with progenitor mass estimates by applying an exciting new technique to HST archival data in M31 and M33. Through detailed modeling of the stellar populations surrounding the location of any known SNe, we can constrain the progenitor mass. Since supernova remnants (SNRs) mark the locations of SNe for the past ~20,000 years and M31 and M33 contain hundreds of these objects, detailed studies of the stellar populations at these locations will constrain the progenitor masses of potentially hundreds of events. After correlating archival HST imaging with the SNR positions, there is useful data for 137 SNRs. We have already measured the progenitor masses for 65 SNRs in M31 and plan to apply our method to 72 SNRs in M33. This proposal will fund the publication of our M31 measurements, analysis of the M33 SNRs, and public release of our photometry. Ultimately, our work will increase the existing sample of SN progenitor masses in the literature by a factor of 20. RESOLVED STELLAR POPULATIONS 12 Small false 0.0 0.0 false false false false SUPPORTED