Molecules and dust in Cassiopeia A

Abstract

We study the dust evolution in the supernova remnant Cassiopeia A. We follow the processing of dust grains that formed in the Type II-b supernova ejecta by modelling the sputtering of grains. The dust is located in dense ejecta clumps that are crossed by the reverse shock. We also investigate further sputtering in the inter-clump medium gas once the clumps have been disrupted by the reverse shock. The dust evolution in the dense ejecta clumps of Type II-P supernovae and their remnants is also explored. We study oxygen-rich clumps that describe the oxygen core of the ejecta, and carbon-rich clumps that correspond to the outermost carbon-rich ejecta zone. We consider the various dust components that form in the supernova, several reverse shock velocities and inter-clump gas temperatures, and derive grain-size distributions and masses for the dust as a function of time. Both non-thermal sputtering within clumps and thermal sputtering in the inter-clump medium gas are studied. We find that non-thermal sputtering in the clumps is important for all supernova types and accounts for reducing the grain population by ∼40% to 80% in mass, depending on the clump gas over-density, the grain type and size, and the shock velocity in the clump. A Type II-b SN forms small grains that are sputtered within the clumps and in the inter-clump medium. For Cas A, silicate grains do not survive thermal sputtering in the inter-clump medium, while alumina, silicon carbide, and carbon dust may survive in the remnant. Our derived masses of currently processed silicate, alumina and carbon grains agree well with the values derived from the observations of warm dust, and seem to indicate that the dust is currently being processed within clumps by non-thermal sputtering. Out of the ∼0.03 M of dust formed in the ejecta, between 30% and 60% of this mass is present today in Cas A, and only 6% to 11% of the initial mass will survive the remnant phase. Grains formed in Type II-P supernovae are larger and better survive their journey in the remnant with mass fractions of surviving dust in the range 14−45%. For very dense ejecta, which describe the ejected material in supernovae such as SN1987A, non-thermal sputtering is inefficient within the clumps and dust survival efficiencies in the remnant range between 42% to 98% in mass. For the SN1987A model, the derived surviving dust mass is in the range ∼0.06−0.13 M . This type of supernovae with dense ejecta may then efficiently provide galaxies with dust. Specifically, silicate grains over 0.1 µm and other grains over 0, 05 µm survive thermal sputtering in the remnant. Therefore, pre-solar grains of supernova origin that are found in meteorites, in particular silicate and alumina grains, possibly form in the dense ejecta clumps of Type II-P supernovae.

Dust destruction by the reverse shock in the Cassiopeia A supernova remnant

“…Recently, Biscaro & Cherchneff (2016) derived a dust mass survival fraction between 6 and 11%, using the analytical model of Truelove & McKee (1999) and the SN dust composition and size distribution of Biscaro & Cherchneff (2014). All models discussed above (except Biscaro & Cherchneff 2016) assumed that the dust grains are embedded in homogeneous ejecta. Silvia et al (2010Silvia et al ( , 2012 performed 3D numerical simulations of the interaction of planar shocks with dense spherical clumps for a range of shock velocities, clump-ejecta density contrasts, and clump metallicities.…”

The dust mass in Cassiopeia A from a spatially resolvedHerschelanalysis

“…The destruction efficiency, furthermore, seems to depend on grain composition, with average destroyed fractions of 20, 38, 80 and 100 % grains for Fe, C, SiO2 and Al2O3 grains (Silvia et al 2010), respectively. Biscaro & Cherchneff (2016) found that non-thermal sputtering in dust clumps in Cas A plays an important role in dust destruction and predicted that it would reduce the current SN dust mass by 40 to 80 %. The largest grain radii that they considered for the Cas A case were < 0.02 µm.…”

Akari Near-Infrared Spectroscopy of the Extended Green Object G318.05+0.09: Detection of Co Fundamental Ro-Vibrational Emission

“…Cas A is a SNR of 340 years old and it is the only SNR in which both high-J rotational and ro-vibrational lines of warm CO gas have been detected (Rho et al 2012;Wallström et al 2013). Processing and evolution of dust and gas in SN ejecta after the explosion, in particular the effects of the reverse shock, have been becoming an important issue for the understanding of the net dust formation yield in SNe (Bianchi & Schneider 2007;Nozawa et al 2007Nozawa et al , 2010Nath et al 2008;Silvia et al 2010aSilvia et al , 2012Gall et al 2014;Dwek & Arendt 2015;Wesson et al 2015;Biscaro & Cherchneff 2016). Biscaro & Cherchneff (2014) show that dust and molecules in ejecta clumps are destroyed by the reverse shock, whereas CO gas can reform in the post-reverse shock gas, but dust clusters do not.…”

“…Biscaro & Cherchneff (2014) show that dust and molecules in ejecta clumps are destroyed by the reverse shock, whereas CO gas can reform in the post-reverse shock gas, but dust clusters do not. Processing of dust and gas in the post-reverse shock clumps depends sensitively on the environmental conditions (Biscaro & Cherchneff 2016). While no information is available of the SNR with which S2 is associated, if it is confirmed to be SN ejecta, further studies of S will provide important information on the study of the physical and chemical conditions of the ejecta.…”