Light Echoes As Probes of Stellar Evolution

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Light echoes from supernova SN1987A, the closest supernova in nearly four centuries, are powerful tools for studying a wide range of processes in stellar evolution. The echoes allow us to map the three dimensional distribution of matter around the supernova, perform direct simple measurements of the scattering properties of interstellar dust, reobserve the ultraviolet pulse that resulted from the supernova shock breaching the progenitor's stellar surface, and determine the temperature and density of gas with direct measurement of recombination times. With these tools Dr. Crotts will map the three dimensional structure of the interstellar medium in a large volume of the Large Magellanic Cloud, and correlate this structure with the large scale motion of gas and sites of active star formation. He will also investigate the past mass loss from the supernova progenitor itself, and describe in detail the evolution of the star's mass loss behavior prior to the explosion. He will study the process of the supernova shock accelerating the progenitor's surface, both by observing the echoed flux from the event, and by mapping in detail the surrounding material that will interact with the highest velocity ejecta on the order of a decade from now, so that the pattern of ejection from the stellar surface can then be inferred.