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

¹ Institute of Astronomy & Astrophysics, National Observatory of Athens, I. Metaxa & V. Paulou, P. Penteli, 15236 Athens, Greece e-mail: [ptb;xilouris;johnal;thk;cgoudis]@astro.noa.gr
² Astronomical Laboratory, Department of Physics, University of Patras, 26500 Rio-Patras, Greece e-mail: pechris@upatras.physics.gr
³ Technological Education Institute of Crete, Department of Sciences, PO Box 1939, GR-710 04 Heraklion, Crete, Greece e-mail: fotis@stef.teiher.gr

Received: 4 December 2008
Accepted: 18 March 2009

Abstract

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 Hα+[ 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]/Hα ratio is greater than 1.2. The Spitzer images at 8 μm and 24 μm 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]/Hα > 1.5). The absence of [O iii] emission indicates slow shock velocities into the interstellar clouds” (≤100 km s^-1), while the [S ii]6716/6731 ratio indicates electron densities up to ~200 cm^-3. The Hα emission is measured to lie between 1.8 to 4.6  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.