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Discovery of Outlying, High-Velocity Oxygen-Rich Ejecta in Cassiopeia A

R. A. Fesen·M. C. Hammell·J. Morse·R. A. Chevalier·K. J. Borkowski·M. A. Dopita·C. L. Gerardy·S. S. Lawrence·J. C. Raymond·S. van den Bergh
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Abstract

Hubble Space Telescope images of the young Galactic supernova remnant Cassiopeia A reveal a far larger population of outlying, high-velocity knots of ejecta with a broader range of chemical properties than previously suspected. We identify three main classes of outer ejecta: 1) Knots dominated by [N II] 6548,6583 emission; 2) Knots dominated by oxygen emission lines especially [O II] 7319,7330; and 3) Knots with emission line strengths similar to the [S II] strong FMK ejecta commonly seen in the main emission shell. The discovery of a significant population of O-rich ejecta situated in between the suspected N-rich outer photospheric layer and S-rich FMK-like ejecta suggests that the Cas A progenitor's chemical layers were not completely disrupted by the supernova explosion outside of the remnant's NE and SW high velocity `jet' regions. In addition, we find the majority of O-rich outer ejecta at projected locations out beyond (v = 6500 - 9000 km/s) the remnant's fastest moving Fe-rich X-ray emission material (6000 km/s) seen in Chandra and XMM data along the eastern limb. This suggests that penetration of Fe-rich material up through the S and Si-rich mantle did not extend past the progenitor's N or O-rich outer layers for at least this section of the remnant.

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R. A. Fesen, M. C. Hammell, J. Morse, R. A. Chevalier, K. J. Borkowski, M. A. Dopita, C. L. Gerardy, S. S. Lawrence, J. C. Raymond, S. van den Bergh. 2005-09-03. Discovery of Outlying, High-Velocity Oxygen-Rich Ejecta in Cassiopeia A. https://doi.org/10.1086/498092

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