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W.P.S. Meikle (Imperial College London)
For over thirty years it has been hypothesised that core-collapse supernovae are, or have been, a major source of dust in the universe. However, only in a very few cases has dust condensation in supernova ejecta been directly and convincingly demonstrated. Two methods are employed. In one procedure, the relative fading of the red wings of the broad optical or near-infrared spectral lines is used to infer the formation of attenuating dust. In the other method, evidence of newly-formed grains can be sought via thermal infrared emission. The characteristic temperature of condensing dust peaks in the mid-infrared region. However, apart from the exceptionally nearby SN 1987A, we have only recently been able to seek mid-infrared emission from supernovae. This has been made feasible by the advent of new infrared facilities, especially the Spitzer Space Telescope.
To use the infrared flux from a supernova to demonstrate grain condensation, we must proceed cautiously. At least 10 core-collapse supernovae have shown late-time near-infrared emission implying the presence of hot dust. But in many cases the radiation may have been due to an infrared "echo" i.e. if the progenitor produces a dusty wind, the early-time luminosity of the supernova can heat this dust yielding a high infrared luminosity. To distinguish between the condensation and IR-echo scenarios it is important to monitor the infrared emission over a wide spectral and temporal range. Ground-based monitoring of the Type IIn SN 1998S out to a wavelength of 4.7 microns has provided some of the most convincing evidence to date about the occurrence and location of dust formation in supernova ejecta. While the near-infrared range is valuable, potentially the most useful information lies in the largely unexplored region at even longer wavelengths. The Spitzer Space Telescope has started to provide this vital information.
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Bulletin of the American Astronomical Society, 37 #2
© 2005. The American Astronomical Soceity.