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H. E. Bond (STScI), A. Henden (USNO), N. Panagia, W. B. Sparks (STScI), S. Starrfield (Arizona State U.), R. M. Wagner (U Arizona)
V838 Mon is an extremely peculiar novalike variable whose outburst was discovered in 2002 January. Unlike classical novae, its spectrum has remained that of a late-type stellar photosphere throughout the outburst. Starting in 2002 February, a rapidly evolving light echo appeared around the star. We have begun a program of imaging polarimetry of the light echo, using the newly installed Advanced Camera for Surveys (ACS) on the Hubble Space Telescope, along with ground-based imaging, photometry, and spectroscopy.
At this writing, we have obtained ACS images in April, May, and September, with two more visits scheduled before the Seattle meeting. The ACS images reveal a wealth of sub-arcsecond structure in the light echo, whose appearance varies dramatically as the light-echo paraboloid expands with time and samples different cuts through the circumstellar dust. In addition to the fine-scale cirrus-like structures, it appears that the dust contains a series of several discrete shells around the star, and a large central cavity. Our images can provide a geometric distance to the star, using two independent methods: (1) determining the exponent of the time dependence of the angular radii of the shells as a function of angular radius, and (2) determining the location of maximum linear polarization in the echoes; this marks material lying a distance c\Delta t from the star in the plane of the sky, where \Delta t is the time since the outburst. At this writing, these methods are suggesting that the distance lies in the approximate range of 3 to 7 kpc.
The absolute magnitude of the star at the maximum of its outburst was therefore in the range MV=-7 to -9. V838 Mon may be related to a red variable (``M31 RV'') that appeared in M31 in the late 1980's, with a similar absolute magnitude, light curve, and late-type spectrum.
The author(s) of this abstract have provided an email address for comments about the abstract: bond@stsci.edu
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.