Supernova remants in M 31.

Image-tube photographs of eight fields in M3 1, using interference filters that isolate Hα + [N II] and [S II], have revealed nebulae that may be supernova remnants in this galaxy. Spectroscopic observations show that 11 of these nebulae resemble galactic supernova remnants (SNRs). The [O III] temperatures determined for four of these SNRs are in the range of 37,000-65,000 K. The [S II] ratios indicate densities in the S⁺ zone in the range of 150-730 cm^-3. 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 E₀ 3 × 10⁵⁰ 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. Interpretation of the remnant spectra through shock-wave models suggests an increase in the nitrogen abundance by a factor of 4 from the outermost SNR near 20 kpc to the innermost near 4 kpc. Some of these SNRs might be detectable as radio sources with the Very Large Array (VLA) telescope; two of them are coincident with Einstein X-ray sources.