Discovery of optical emission from the supernova remnant G 32.8-0.1 (Kes 78)

Deep optical CCD images of the supernova remnant G 32.8-0.1 were obtained where filamentary and diffuse emission was discovered. The images were acquired in the emission lines of H alpha + [N II] and [S II]. Filamentary and diffuse structures are detected in most areas of the remnant, while no significant [O III] emission is present. The flux-calibrated images suggest that the optical emission originates from shock-heated gas since the [S II]/H alpha ratio is greater than 1.2. The Spitzer images at 8 mu m and 24 mu m show a few filamentary structures to be correlated with the optical filaments, while the radio emission at 1.4 GHz in the same area is found to be very well correlated with the brightest optical filaments. The results from deep long-slit spectra also support the origin of the emission being from shock-heated gas ([S II]/H alpha > 1.5). The absence of [O III] emission indicates slow shock velocities into the interstellar "clouds" (<= 100 km s(-1)), while the [S II]lambda lambda 6716/6731 ratio indicates electron densities up to similar to 200 cm(-3). The H alpha emission is measured to lie between 1.8 to 4.6 x 10(-17) erg s(-1) cm(-2) arcsec(-2), while from VGPS HI images the distance to the SNR is estimated to be between 6 to 8.5 kpc.