Dust Destruction in Shock Waves in the Cygnus Loop

Abstract

Supernova remnant (SNR) shock waves are known to be important sources of dust destruction in the interstellar medium. Models of dust destruction in shocks have made various predictions of the destruction efficiency, but have generally been difficult to test in detail due to the uncertainties in the physical parameters in observed shocks and the required assumptions in the models. In this paper we present new Hubble Space Telescope data on shocks in the Cygnus Loop SNR that have been observed with enough precision over time to allow determination of their proper motions and thus the shock speeds. The observed UV emission comes from various ions from elements that are prevalent in dust. We present results of new models for these radiative shocks that include dust destruction, including the liberation of elements into the gas phase. The inclusion of sputtered grain material substantially alters the predicted cooling and spectra and gives us a better estimate of the effects of dust on the shock emission. The observed line ratios strongly support the predictions that radiative shocks with speeds vs = 90–160 km s−1 destroy dust with an efficiency that increases with shock speed approximately with the predicted rates.