SIMBAD references

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.