AAS Meeting #193 - Austin, Texas, January 1999
Session 74. Supernova Remnants
Display, Friday, January 8, 1999, 9:20am-6:30pm, Exhibit Hall 1

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[74.02] HST-WFPC2 Imaging of Faint Balmer Filaments in the Cygnus Loop

R. Sankrit, W. P. Blair (Johns Hopkins Univ.), J. C. Raymond (Harvard-Smithsonian CfA), K. S. Long (STScI)

At the north-east edge of the Cygnus Loop supernova remnant, there is a network of faint filaments whose optical emission line spectrum is dominated by the Balmer lines of hydrogen. These filaments trace the shock front formed by the blastwave from the supernova explosion interacting with the walls of the cavity in which the supernova exploded.

As part of a Cycle 7 HST-STIS project for which the ultimate goal is to obtain spectra of these filaments at high spatial resolution, an EARLY ACQUISITION narrow band H\alpha image was taken with the WFPC2. We present this image, which shows the network of filaments in exquisite detail. The shock front is seen to be a gently rolling sheet lying more or less along the line of sight and reducing to a width of one WFC pixel or less when it is exactly edge on.

We estimate the H\alpha flux from the filaments and calculate shock models which match these observations. We then present the predicted strengths of important UV lines expected in the spectrum of the postshock gas. We show how the model calculations can be compared with high spatial resolution STIS spectra (to be obtained in mid-1999) to constrain the shock properties, and resolve the issue of whether the ions and electrons just behind the shock front come to rapid equilibrium or are more slowly equilibrated via Coulomb processes.

This work is supported by STScI grant GO-07289.01-96A to The Johns Hopkins University.

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