Astronomy and Astrophysics, volume 317, 203 (1997/1-1)
Neutral hydrogen compact absorption features in Cassiopeia A.
REYNOSO E.M., GOSS W.M., DUBNER G.M., WINKLER P.F. and SCHWARZ U.J.
Abstract (from CDS):
Very Large Array (VLA) observations of the λ21 cm H I line towards Cassiopeia A (Cas A) have been performed. The velocity interval observed was from -38 to -362(LSR)km/s, with a resolution of 2.6km/s and a beam size of 14.2"x11.4". Opacity images show the presence of a number of small absorption H I features in the velocity interval -62 to -69km/s (LSR) which, on the basis of several arguments, are postulated to be physically associated with Cas A. These cold H I knots have sizes of <0.1pc and show spatial substructure. Their velocities lie well outside the range of the intervening H I in the Perseus spiral arm, i.e. 0 to -55km/s. We demonstrate that the H I knots cannot be described as shocked interstellar cloudlets engulfed by the blast wave of the supernova remnant (SNR). Instead, we propose that these low velocity H I features are recombined wind driven clumps moving ahead of the supernova (SN) shock front. This hypothesis is supported by the ages derived for the knots, varying from 8x103 to 5x104years, which implies that these features were originally accelerated during the Wolf-Rayet (WR) phase of the precursor star.
ISM: supernova remnants - ISM: individual: Cas A - stars: mass loss