A Study of Extragalactic Supernova Remnants.

Image tube photographs of eight fields in the nearby spiral. galaxy M31, using interference filters that isolate the emission lines. of H(alpha) + {N II} at (lamda)6570 (ANGSTROM) and {S II}(lamda)6725 (ANGSTROM), have revealed nebulae. that we believe to be supernova remnants (SNRs) in this galaxy. Spectroscopic observations have been used to confirm this. identification for twleve of these nebulae. An estimate of the. pressure in the optical filaments and the measured diameter. permit an estimate of the initial energy in each remnant; we find a mean value of E(,0) (TURNEQ) 3 x 10('50) ergs. However, the energy calculated in this way appears to be correlated with the remnant's diameter, an effect which may be related to magnetic pressure in the filaments. Comparison of our SNR spectra to shock wave models has allowed us to estimate abundances of nitrogen, oxygen and sulfur in the interstellar gas of M31. We have also observed eleven H II regions in M31 for comparison to the SNRs. Element abundances for these have been derived by an empirical method and are in substantial agreement with the abundances as derived from the SNRs. The variation of abundances as a function of galactocentric distance in M31 are found to be similar to the abundance gradients in our own Galaxy, with nitrogen and oxygen both decreasing by a factor of four or five from 4 to 23 Kpc. We have also investigated an emission region in the irregular. galaxy NGC 4449 which is believed to be a very luminous, young. SNR similar to the galactic remnant Cassiopeia A. From optical spectrophotometry we find broad emission lines of {O I}(lamda)(lamda)6300,6363; {O II}(lamda)(lamda)3727,7325; {O III}(lamda)(lamda)4363,4959,5007; {S II}(lamda)4070 and {Ne III}(lamda)3869 with widths that suggest an expansion at 3500 km s('-1). From the fluxes in the oxygen lines, we find that about 0.1 M(,(CIRCLE)) of oxygen is present in the gas that is presently cooling. The absence of hydrogen in the oxygen rich knots suggests that nucleosynthesis has been important in the star that created this remnant. Combining the optical data with x-ray observations from the HEAO-B (Einstein) X-ray Observatory, we have been able to derive a consistent overall picture of the interaction between the SNR and the H II region in which it is embedded.