SIMBAD references

We present narrowband images of the Kepler supernova remnant obtained with the Advanced Camera for Surveys aboard the Hubble Space Telescope. The images, with an angular resolution of 0.05', reveal the structure of the emitting gas in unprecedented detail. Radiative and nonradiative shocks are found in close proximity, unresolvable in ground-based spectra, indicating that the pre-shock medium is highly clumped. The ionization structure, traced by differences in the [O III] to [N II] flux ratio, varies on subarcsecond scales. The variation is due to both differences in shock velocity and gradients in the evolutionary stage of the shocks. A prominent complex of knots protruding beyond the boundary of the remnant in the northwest is found to consist of bright radiative knots, connected by arcuate nonradiative filaments. Based on the coincidence of the optical emission with a bright isolated knot of X-ray emission, we infer that this feature is due to a Rayleigh-Taylor finger that formed at the contact discontinuity and overtook the primary blastwave.