V838 Monocerotis, which burst upon the astronomical scene in early 2002, is a completely unanticipated new object. It underwent a large-amplitude and very luminous outburst, during which its spectrum remained that of an extremely cool supergiant. A rapidly evolving set of light echoes around V838 Mon was discovered soon after the outburst, and quickly became the most spectacular display of the phenomenon ever seen. These light echoes provide the means to accomplish three unique types of measurements based on continued HST imaging during the event: (1) Study effects of MHD turbulence at high resolution and in 3 dimensions; (2) Construct the first unambiguous and fully 3-D map of a circumstellar dust envelope in the Milky Way; (3) Study dust physics in a unique setting where the spectrum and light curve of the illumination, and the scattering angle, are unambiguously known. We have also used our HST data to determine the distance to V838 Mon through direct geometric techniques. Because of the extreme rarity of light echoes, this is almost certainly the only opportunity to achieve such results during the lifetime of HST. We propose two visits during Cycle 16, in order to continue the mapping of the circumstellar dust and to accomplish the other goals listed above.

This program contains two visits, 5 orbits each, for imaging of the light echo around V838 Mon with the WFPC2. Images will be taken in V (F606). We will use 2 pointings with dithering to cover the entire echo. The two visits during Cycle 16 are placed as far apart as possible, at the beginning and end of the target visibility season. One visit will be in September 2007, and the other in February 2008. ISM AND CIRCUMSTELLAR MATTER 12 false 0.0 false false false false false false SUPPORTED ISM EJECTA PLANETARY NEBULA REFLECTION NEBULA WIND Geometric center of light echo, based on ACS images obtained in September 2006. 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