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Title:
Discovery of Outlying High-Velocity Oxygen-Rich Ejecta in Cassiopeia A
Authors:
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.; van den Bergh, Sidney
Affiliation:
AA(Department of Physics and Astronomy, 6127 Wilder Laboratory, Dartmouth College, Hanover, NH 03755.), AB(Department of Physics and Astronomy, 6127 Wilder Laboratory, Dartmouth College, Hanover, NH 03755.), AC(Department of Physics and Astronomy, Arizona State University, Box 871504, Tempe, AZ 85287.), AD(Department of Astronomy, University of Virginia, P.O. Box 3818, Charlottesville, VA 22903.), AE(Department of Physics, North Carolina State University, Box 8202, Raleigh, NC 27695.), AF(Research School of Astronomy and Astrophysics, Australian National University, Cotter Road, Weston Creek, ACT 2611, Australia.), AG(Astrophysics Group, Imperial College, Blackett Laboratory, Prince Consort Road, London SW7 2BZ, UK.), AH(Department of Physics and Astronomy, Hofstra University, Hempstead, NY 11549.), AI(Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138.), AJ(Dominion Astrophysical Observatory, Herzberg Institute of Astrophysics, NRC of Canada, 5071 West Saanich Road, Victoria, BC V9E 2E7, Canada.)
Publication:
The Astrophysical Journal, Volume 636, Issue 2, pp. 859-872. (ApJ Homepage)
Publication Date:
01/2006
Origin:
UCP
ApJ Keywords:
ISM: Abundances, ISM: Individual: Name: Cassiopeia A, ISM: Kinematics and Dynamics, ISM: Supernova Remnants
DOI:
10.1086/498092
Bibliographic Code:
2006ApJ...636..859F

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. In this paper, we concentrate on a ~=1.5 arcmin2 region located along the eastern limb of the remnant where we identify three main classes of outer ejecta: (1) knots dominated by [N II] λλ6548, 6583 emission, (2) knots dominated by oxygen emission lines, especially [O II] λλ7319, 7330, and (3) knots with emission-line strengths similar to the [S II]-strong fast-moving knot (FMK) ejecta commonly seen in the main emission shell. Mean transverse velocities derived from observed proper motion for N-rich, O-rich, and FMK-like knots 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 between the suspected N-rich outer photospheric layer and S-rich FMK-like ejecta suggests that the progenitor's chemical layers were not completely disrupted by the supernova explosion outside of the remnant's northeast and southwest high-velocity ``jet'' regions. In addition, we find the majority of O-rich outer ejecta at projected locations out beyond the remnant's fastest moving Fe-rich X-ray emission material seen in Chandra and XMM-Newton data along the eastern limb, suggesting 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 this section of the remnant.

Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.

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