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J. Rho (Caltech), T. Kozasa (Hokkaido U.), J. Smith (UAZ), L. Rudnick, J. Ennis (UMN), W. Reach (Caltech), T. DeLaney (CfA), H. Gomez (Cardiff U.)
Dust formation in supernovae has long been invoked to understand the large depletions of refractory elements in the ISM. Recent discovery of huge quantities of dust in galaxies and quasars at very high redshift suggests that dust was produced efficiently in the first generation of supernovae. Young supernova remnants are viable laboratories to study dust formation and the Cassiopeia A supernova remnant is the best site for it.
We performed Spitzer IRS mapping observations of Cassiopeia A. Our IRS mapping covers the entire supernova remnant of Cas A, producing mid-infrared spectra every ~5 arcsec. The gas lines and continuum both were strong for most of positions, and gas lines include Ar, Ne, O, Si, S and Fe. A few dust features are identified using spectroscopy and a line-free dust map (19-23 micron) which is closely resembles the ejecta maps such as [Ar II], [O VI], and [Ne II]. A dominant dust feature is continuum which peaks at 21 micron, not seen in other astronomical objects and previously interpreted as a unique class of silicates minerals. Most of the brightest parts of the dust maps are dominated by this type of dust, and this dust is strongly correlated to [Ar II], [OIV], and [Ne II] emission, implying that dust is freshly formed in the ejecta. A second dust feature we identified is silicate emission features around 9.8 micron corresponding to the stretching mode. Most interestingly, we identified another type of dust, featureless dust, from a few positions from the dust maps, where the ejecta lines are not prominent and yet they are not from the forward shock region. Our observations confirm that the young supernova remnant Cas A is an active site of dust formation. We will discuss dust properties such as dust composition, grain sizes, temperatures of the dust, and dust formation conditions from this unique dust forming sites of the Cassiopeia A young supernova remnant.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.