Nucleosynthesis Layers and Dust Formation in Cas A

Details Nucleosynthesis Layers and Dust Formation in Cas A Nucleosynthesis Layers and Dust Formation in Cas A

Jun 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006aas...208.5901r&link_type=abstract

American Astronomical Society Meeting 208, #59.01; Bulletin of the American Astronomical Society, Vol. 38, p.139

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The combination of Spitzer IRAC and MIPS images and IRS 5-38 micron mapping has allowed us to isolate both the shocked circumstellar dust and the freshly formed dust in the Cassiopeia A supernova remnant. While the circumstellar dust is most clearly seen associated with the X-ray and radio and IRAC Channel 1 (synchrotron) forward shock regions, the freshly formed dust is associated with the ejecta. Ionic lines such as [Ar II] trace the distribution of the freshly formed dust, which shows a prominent spectral peak at 21 microns. Mg proto-silicates likely dominate this peak, with other silicate stretching modes visible around 9.8 microns. This dust therefore arises from deep in the O-burning layers of the explosion. We find, in isolated positions, a new type of featureless dust spectrum, whose emission appears dominated by Al2O3, and where the ionic lines of [Ar II], [Si II] and [S III] are relatively weak. This dust likely arises from higher, C-burning layers of the explosion. IRAC images from Channels 2, 3, and 4 reveal different nucleosynthetic layers, and imply asymmetries deep in the explosion which preserve these layers with little radial mixing. We conclude that the dust and ionic lines in the mid-infrared, and the hotter and more highly ionized optical and X-ray emission are then dominated by the nucleosynthesis layer currently encountering the reverse shock in each specific direction. We will briefly present evidence for other mixtures of dust components with the grain sizes and temperatures and correlation between the dust composition and the ionic lines of ejecta.This work is based, in part, on observations with the Spitzer Space Telescope, through an guest observer award issued by JPL/Caltech.

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