0 Assigned ID: 165 ----- Attempting Submission 1 (Wed Apr 05 19:38:51 GMT 2017) ----- ----- Attempting Submission 2 (Sat Apr 08 12:42:35 GMT 2017) ----- HST has played a crucial role in elucidating the environments, progenitors, explosions, and late-time behavior of Type IIn supernovae (SNe) and binary star mergers (also known as common envelope events). Although shock interaction plays a dominant role in the dynamics and appearance of these events, the details of this process and the nature of the mass loss leading up to the core collapse or dynamical stage of the merger, remain poorly understood. Mounting evidence suggests that the pre-explosion mass loss geometry is a disk or equatorially-concentrated outflow. We will perform the first multi-dimensional radiation hydrodynamical simulations of the shock interaction between the fast ejecta from the SN explosion/dynamical merger and a slower equatorially-focused outflow representing the earlier phase of mass loss. Our calculations will quantify the geometry of the ejecta and make detailed predictions for the shock-powered emission. In combination with an analytic model to be developed in parallel, we will translate the light curves and spectral information on a large sample of IIn SNe and stellar mergers into probes of their mass loss history. We will address whether the combination of hydrogen recombination and shock-powered emission can explain the common double-peaked nature of the light curves of stellar mergers. By accounting self-consistently for the role of radiative shock compression on the ejecta density structure, and thus on the global geometry and microphysical properties of dust grains formed, we will also address the late-time appearance of IIn SNe and stellar mergers observed by HST and JWST. Stellar Physics Stellar Populations 0 Regular false false true SUPPORTED