| We present results from a modeling effort of simple shock phenomena in the Cygnus Loop and Cassiopeia A. Using multi-epoch MDM observations of a small, isolated cloud in the southwest region of the Cygnus Loop, we measure the velocity of the Balmer-dominated shock filaments as well as the velocity of the internal cloud shock. These results are used to constrain the primary parameter for interstellar clouds: the density contrast between the cloud and the interstellar medium. These results are used to present models for a strong shock interacting with a lumpy, but diffuse cloud. This model represents a refinement over previous shock-cloud models.; Using multi-epoch X-ray observations of the Cassiopeia A supernova remnant, we investigate a small bow shock which protrudes north of the identified forward shock front. Proper motion estimates for this object, combined with a spectral analysis suggest that the object is a bullet of ejecta, similar to those found in Vela. Model results are presented which show the evolution of an ejecta bullet across the SNR. These simulations suggest that bullet ejecta could arise in Cas A, and that the bullet material could survive the turbulent journey through shocked ejecta.; Finally, preliminary results from a study of the reverse shock structure in Cas A are presented. We present regions which show decaying fluxes over a four year period, but also show an increase in X-ray line emission, suggesting that the gas in these regions is approaching ionization equilibrium. Models for reverse shock formation and the reverse shock-ejecta interaction are discussed. |
