Formation and Evolution of Dust and Molecules in the Inhomogeneous Ejecta of Cassiopeia A

Tuesday, April 26, 2016 - 3:30pm PDT
Chiara Biscaro
University of Copenhagen
N232, Room 227
Event Type: 

Dust and molecules are observed in various supernovae and their remnants, but their formation and evolution in these hostile, shocked environments are still unclear. In the 330 years-old remnant Cas A, the reverse shock is currently reprocessing the material formed in the supernova ejecta. Our aim is to assess whether supernovae are important contributors to the dust budget of galaxies. The Cas A remnant results from the explosion of a 19 Msun star as a Type IIb supernova characterised by a low-density ejecta. We first model the formation of molecules, dust clusters, and dust grains in the supernova ejecta to derive dust grain size distributions. We then model the impact of the reverse shock on oxygen- and carbon-rich ejecta clumps, and investigate the post-shock chemistry by considering various reverse shock velocities. We study the destruction of molecules and dust clusters by the shock, and their reformation using a chemical kinetic model, and investigate the effect of thermal and non-thermal sputtering on the dust within the clumps. Our results show that only medium- and large-sized grains survive non-thermal sputtering in dense clumps, and that small dust grains do not efficiently reform in the shocked gas. This result indicates that the dust formed in the supernova ejecta and destroyed by the reverse shock is unable to reform from the gas phase in the remnant. We then investigate the effect of thermal sputtering on the clump dust
injected into the high-temperature interclump medium over several clump-crushing times. Oxide grains are almost completely destroyed, pointing to the inability of SN Type IIb to contribute significantly to the galactic dust budget. Large grains, such as formed in Type IIP
SNe as 1987A, are required to survive the remnant phase. SNRs with dense clumps and dust grain size distributions including large grains can be significant contributors to the dust budget in the early as well as in the local universe.


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