Assigned ID: 1013 ----- Attempting Submission 1 (Sat Feb 25 00:38:36 GMT 2012) ----- HST Phase I Proposal 1013 (LEM31.apt) successfully submitted. ----- Attempting Submission 2 (Sat Feb 25 00:49:10 GMT 2012) ----- HST Phase I Proposal 1013 (LEM31.apt) successfully submitted. ----- Attempting Submission 3 (Sat Feb 25 00:54:23 GMT 2012) ----- The PHAT legacy survey of M31 is a rich repository of data that has not yet been systematically mined for transients and variables. We propose to apply difference imaging to all suitable pairs of images in this extensive ongoing survey and to a smaller extent other previous observations of M31. Our main scientific goal is to discover light echoes of ancient SNe and other bright eruptive transients like LBVs in the subset of difference images for which the two epochs were separated by 6 months. With the brightest of these echoes, we can do follow-up spectral classification of the source event, determine their ages, and determine properties of the scattering dust. However, our difference image data products will also greatly improve on the detection and characterization of variables and transients of all kinds using generic photometry in crowding-limited fields like M31. We will make these data available through the MAST archive so that they are easy to access and search by archival investigators and will cross-match with other internal or external catalogs from current M31 surveys like Pan-STARRS1 and PTF. This will add a new legacy aspect to these data by providing access to the time variable domain. ISM IN EXTERNAL GALAXIES 12 Legacy false 0.0 0.0 false false false false SUPPORTED