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

TL;DR

This study presents the first optical detection of filamentary and diffuse emission from supernova remnant G 32.8-0.1, revealing shock-heated gas characteristics and correlating optical, infrared, and radio observations to understand its properties.

Contribution

First deep optical CCD imaging and spectral analysis of G 32.8-0.1, confirming shock-heated gas emission and correlating multi-wavelength data for this supernova remnant.

Findings

Optical filaments detected in Halpha+[N II] and [S II] lines.

Shock-heated gas indicated by [S II]/Halpha ratio > 1.2.

Correlation between optical filaments and infrared/radio emissions.

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 Halpha+[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]/Halpha ratio is greater than 1.2. The Spitzer images at 8 micron and 24 micron 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. Furthermore, the results from deep long-slit spectra also support the origin of the emission to be from shock-heated gas ([S II]/Halpha > 1.5). The absence of [O III] emission indicates slow shocks velocities into the interstellar "clouds" (< 100 km/s), while the [S II] 6716/6731 ratio indicates electron densities up to ~200 cm^{-3}. Finally, the Halpha emission is measured to lie between 1.8 to 4.6 x 10^{-17} erg/s/cm^2/arcsec^2, while from VGPS HI images a distance to the SNR is estimated to be between 6 to 8.5 kpc.