17210

The supernova remnant Cassiopeia A (Cas A) provides the clearest look at the properties and explosion dynamics of a core-collapse supernova (CCSN). With an explosion date around 1670 comma Cas A is the youngest Galactic core-collapse SNR known and comma at an estimated distance of 3.4 kpc comma it is also among the closest and brightest. However comma Cas A exhibits significant changes in its emission structure on timescales as short as 1-2 years comma and large-scale changes in one or two decades comma meaning that upcoming multi-wavelength investigations require nearly contemporaneous comma high-resolution optical observations. This proposal describes a multi-bandpass ACS imaging program with the goals ofdoublePoint 1) a high-resolution optical survey that can discriminate O-Ne rich ejecta from S-Ar-Ca rich ejecta comma thereby assisting new multi-wavelength studies of Cas A.s ejecta and its dust content comma including JWST approved Cycle 1 Near and Mid-IR observations comma deep new 50 to 100 ksec Chandra high spatial resolution X-ray observations comma and high spectral resolution X-ray data from the upcoming XRISM mission comma 2) resolve the remnant.s newly emerging and freshly reverse shocked O-Ne rich and S-Ar-Ca rich ejecta along the southern limb and north-central region comma 3) add new constraints on reverse shock velocity estimates across multiple regions comma and 4) measure the proper motions of the remnant.s highest-velocity (8000 to 14 comma 500 km-s) outer ejecta providing improved age and explosion center estimates plus deceleration measurements probing the density and arrangement of the local circumstellar medium as well as ejecta knot lifetimes.