13,595 research outputs found
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
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