Document Type
Article
Publication Date
2006
Publication Title
The Astrophysical Journal
Department
Department of Physics and Astronomy
Abstract
Analysis of broadband HST ACS and WFPC2 images of the young Galactic supernova remnant Cassiopeia A reveals a far larger population of outlying, high-velocity knots of ejecta with a broader range of chemical properties than previously suspected. ACS filte r flux ratios along with follow-up, ground-based spectra are used to investigate some of the kinema tic and chemical properties of these outermost ejecta. In this paper, we concentrate on a ≃ 1.5 sq arcmin region located along the eastern limb of the remnant where numerous outer emission knots are optica lly visible due to an interaction with a local circumstellar cloud, thereby providing a more complete an d unbiased look at the remnant’s fastest debris fragments. From a study of this region, we identify three main classes of outer ejecta: 1) Knots dominated by [N II] λλ 6548,6583 emission; 2) Knots dominated by oxygen emission lines especially [O II] λλ 7319,7330; and 3) Knots with emission line strengths similar to the [S II ] strong FMK ejecta commonly seen in the main emission shell. We identified a tota l of 69 [N II], 40 [O II], and 120 [S II] knots in the small eastern limb region studied. Mean tra nsverse velocities derived from observed proper motion for 63 N-rich, 37 O-rich, and 117 FMK-like k nots identified in this region were found to be 8100, 7900, and 7600 km s − 1 , respectively. 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 tha t the Cas A progenitor’s chemical layers were not completely disrupted by the supernova explosion ou tside of the remnant’s NE and SW high velocity ‘jet’ regions. In addition, we find the majority of O-r ich outer ejecta at projected locations out beyond (v = 6500 − 9000 km s − 1 ) the remnant’s fastest moving Fe-rich X-ray emission material (6000 km s − 1 ) 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 m antle did not extend past the progenitor’s N or O-rich outer layers for at least this section of the remnant.
DOI
10.1086/498092
Original Citation
Robert A. Fesen et al 2006 ApJ 636 859
Dartmouth Digital Commons Citation
Fesen, Robert A.; Hammell, Molly C.; Morse, Jon; Chevalier, Roger A.; Borkowski, Kazimierz J.; Dopita, Michael A.; Gerardy, Christopher L.; Lawrence, Stephen S.; Raymond, John C.; and van den Bergh, Sydney, "Discovery of Outlying High-Velocity Oxygen-Rich Ejecta in Cassiopeia A" (2006). Dartmouth Scholarship. 2644.
https://digitalcommons.dartmouth.edu/facoa/2644
