The optical emission from a fast shock wave with application to supernova remnants

Abstract

The spectrum of Tycho's supernova remnant was observed and only the H-alpha, H-beta, and H-gamma lines were detected. The H-alpha line profile can be divided into two components: one with a width consistent with the instrumental resolution and one with a full width at half-maximum (FWHM) of 1800 plus or minus 200 km/s. The two components have similar intensities. The observations are interpreted in terms of a shock wave model. The shock wave is presumably encountering neutral atoms that have some probability of giving line emission before being ionized by the postshock gas. Charge exchange can occur in the postshock region, giving rise to a broad emission component from a population of fast neutral atoms. For Tycho's remnant, both the ratio of broad to narrow emission and the FWHM of the broad emission can be fitted if the shock velocity is 2300 plus or minus 500 km/s. Combined with the proper motion of the filament as found by Kamper and van den Bergh, the distance to Tycho's remnant is about 2.3 plus or minus 0.5 kpc. The absolute photographic magnitude of Tycho's supernova at maximum is then -18.8 plus or minus 1.3.