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Title:
The Expansion Center and Dynamical Age of the Galactic Supernova Remnant Cassiopeia A
Authors:
Thorstensen, John R.; Fesen, Robert A.; 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(Dominion Astrophysical Observatory, Herzberg Institute of Astrophysics, National Research Council of Canada, 5071 West Saanich Road, Victoria, BC V9E 2E7, Canada)
Publication:
The Astronomical Journal, Volume 122, Issue 1, pp. 297-307. (AJ Homepage)
Publication Date:
07/2001
Origin:
UCP
AJ Keywords:
ISM: individual (Cassiopeia A), ISM: Kinematics and Dynamics, ISM: Supernova Remnants
DOI:
10.1086/321138
Bibliographic Code:
2001AJ....122..297T

Abstract

We present proper motions for 21 bright main shell and 17 faint, higher velocity, outer ejecta knots in the Cas A supernova remnant and use them to derive new estimates for the remnant's expansion center and age. Our study included 1951-1976 Palomar 5 m prime focus plates, 1988-1999 CCD images from the KPNO 4 m and MDM 2.4 m telescopes, and 1999 HST WFPC2 images. Measurable positions covered a 23 to 41 yr time span for most knots, with a few outer knots followed for almost 48 yr. We derive an expansion center of α(J2000)=23h23m27.77s+/-0.05s, δ(J2000)=58°48'49.4"+/-0.4" (ICRS), with little difference between centers derived using outer or main shell knots. This position is 3.0" due north of that estimated by van den Bergh & Kamper. It also lies 6.6"+/-1.5" almost due north (P.A.=354deg) of the remnant's recently detected central X-ray point source, implying a transverse velocity for the X-ray point source ~=330 km s-1 at a distance of 3.4 kpc. Using the knots which lie out ahead of the remnant's forward blast wave, we estimate a knot convergent date of A.D. 1671.3+/-0.9 assuming no deceleration. However, a deceleration of just ~1.6 km s-1 yr-1 over a 300 yr time span would produce an explosion date ~=A.D. 1680, consistent with the suspected sighting of the Cas A supernova by J. Flamsteed. Based in part 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 NAS 5-26555.
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