The peculiar supernova remnant CTB 80

Deep CCD exposures of the peculiar supernova remnant CTB 80 in the light of the H alpha + [N II], [S II], [O II], and [O III] filters have been obtained. These images reveal significant shock heated emission in the area of the remnant. An extended bright diffuse nebula in the south-east part of CTB 80 overlaps soft X-ray emission from ROSAT but it does not appear to be related to the remnant under study. New diffuse and filamentary structures are detected to the south, south-east, and north of PSR 1951+32, most likely associated with CTB 80. Especially, the sulfur line image shows emission in the north along the outer boundary of the IRAS and H I shells. The [O III] emission is filamentary, suggesting shock velocities greater than 100 km s(-1) but its spatial extent is quite limited. Lower shock velocities are expected in the north and north-east areas of the remnant, since [O II] emission is present, while [O III] line emission is not detected. The comparison between the [O III] and[O II] line images further suggest the presence of significant inhomogeneities in the interstellar medium. The flux-calibrated images do not indicate the presence of incomplete recombination zones, and we estimate that the densities of the preshock clouds should not exceed a few atoms per cm(3). The typical projected angular widths of the observed filaments are similar to 30". Typical surface brightness values of the long [O III] filament in the south are similar to 12 10(17) erg s(-1) cm(-2) arcsec(-2) while the [O II] image is characterized by flxes of 10-20 10(-17) erg s(-1) cm(-2) arcsec(-2). The area covered by the optical radiation along with the radio emission at 1410 MHz suggest that CTB 80 occupies a larger angular extent than was previously known.