The infrared diagnostic of a dusty plasma with applications to supernova remnants
IRAS observations of infrared emission from supernova remnants constitute the first observational evidence of shock-heated dust in the interstellar medium. These observations can provide valuable information on the morphology of supernova remnants, and on their interaction with the ambient interstellar medium. In particular, they can be used to study the physical condition and the cooling rate of dusty astrophysical plasmas. In this paper, consideration is given to the possibilities and limitations of using the infrared observations as a diagnostic for the shocked gas, and as a means of determining remnant parameters. The paper presents improved calculations for the cooling rate of a dusty plasma by means of gas-grain collisions, and the equilibrium temperature of the dust for a variety of plasma conditions. These results are then used to define the density-temperature parameter space of the plasma, which, given its infrared spectrum, should be occupied by the observed remnant. This constraint can be used to estimate distances to supernova remnants and to set limits on various parameters that determine their evolution. The analysis is applied to the remnants Cas A and the Cygnus Loop.