Supernova Remnants in the Hα and Hβ Lines

Abstract

Three-dimensional gas-dynamic calculations of the evolution of supernova remnants are used to study the evolution of the emission in the Hα and Hβ recombination lines and the dispersion in the velocities of the ionized gas. The influence of variations in the abundances of chemical elements, in particular, iron, on the thermal and dynamic evolution of a supernova remnant is examined. It is found that the velocity dispersion of the gas in the shell of a young remnant varies over a wide range: essentially from zero to ~100-120 km/s, with a maximum value that decreases with time. Variation in the abundance of iron by ±0.5 dex in a gas with the solar abundance of other elements leads to a change in the thermal structure of a supernova shell and a proportionate change in the intensity of the Hα line emission. The recombination line intensity ratio I(Hα)/I(Hβ) decreases as a remnant ages, so it can serve as an indicator of its evolutionary status and can be used for more accurate identification of the contributions of supernova remnants and HII zones in I(Hα)-σ diagrams. It is shown that the ranges of the velocity dispersion of the gas and the intensity of Hα line emission for supernova shells lie within intervals that are traditionally associated with ionization zones, and this must be taken into account for correct interpretation of observations of star-formation regions in other galaxies.