SUPERNOVA REMNANTS IN MOLECULAR CLOUDS

摘要

Massive (≥ 8 Mo) stars may end their lives in the molecular clouds in which they were born. O-type stars probably have sufficient photoionizing radiation and wind power to clear a region more than l5 pc in radius of molecular material. Early B stars (B1-B3 on the main sequence, or 8-l2 Mo stars) are not capable of this and may interact directly with molecular gas when they explode. Molecular clouds are known to be clumpy, with dense molecular clumps occupying only a few percent of the volume. A super-nova remnant then evolves primarily in the interclump medium, which has a density nH = 5-25 H atoms cm(-3). The remnant becomes radiative at a radius of ~6 pc, forming a shell that is magnetically sup-ported. The structure of the shell can be described by a self similar solution. When this shell interacts with the dense clumps, the molecular shock fronts are driven by a considerable overpressure compared to the pressure in the rest of the remnant. The expected range of clump sizes leads to a complex velocity distribution, with the possibility of molecular gas accelerated to a high velocity. Observations of the remnants W44 and IC 443 can be understood in this model. W44 has a shell expanding at ~ l50 km s~-1 into a medium with density 4-5 cm(-3). The shock emission expected in such a model is consistent with the observed Ha surface brightness and the [O I] 63 mu m line luminosity. The clump interaction is seen in OH maser emission, which shows a magnetic field strength that is consistent with that expected in the model. IC 443 appears to be expanding at a