Supernovae in Molecular Clouds

Supernovae are expected to occur near the molecular material in which the massive progenitor star was born, except in cases where the photoionizing radiation and winds from the progenitor star and its neighbors have cleared out a region. The clumpy structure in molecular clouds is crucial for the remnant evolution; the supernova shock front can become radiative in the interclump medium and the radiative shell then collides with molecular clumps. The interaction is relevant to a number of phenomena: the hydrodynamics of a magnetically supported dense shell interacting with molecular clumps; the molecular emission from shock waves, including the production of the OH 1720 MHz maser line; the relativistic particle emission, including radio synchrotron and gamma-ray emission, from the dense radiative shell; and the possible gravitational instability of a compressed clump.Comment: 10 pages, 2 figures, review for proceedings of the Maryland conference on Young Supernova Remnant

Cassiopeia A and its Clumpy Presupernova Wind

The observed shock wave positions and expansion in Cas A can be interpreted in a model of supernova interaction with a freely expanding stellar wind with a mass loss rate of ~3e-5 Msun/yr for a wind velocity of 10 km/s. The wind was probably still being lost at the time of the supernova, which may have been of Type IIn or IIb. The wind may play a role in the formation of very fast knots observed in Cas A. In this model, the quasi-stationary flocculi (QSFs) represent clumps in the wind, with a density contrast of several 1000 compared to the smooth wind. The outer, unshocked clumpy wind is photoionized by radiation from the supernova, and is observed as a patchy HII region around Cas A. This gas has a lower density than the QSFs and is heated by nonradiative shocks driven by the blast wave. Denser clumps have recombined and are observed as HI compact absorption features towards Cas A.Comment: 13 pages, ApJL, in pres