Radiative shock-wave theory. I - Chemical abundance diagnostics and galactic abundance gradients
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Abstract
Using an extensive grid of fully radiative plane-parallel shock models, the way in which both the visible forbidden and UV intercombination lines may be used for chemical abundance diagnostics in supernova remnants is investigated. It is found that, for shock velocities in excess of a critical value, the emergent spectrum depends primarily on abundance rather than on the shock conditions. Available spectrophotometry confirms this conclusion, and the data are used to show, first, that the oxygen/nitrogen abundance ratio decreases by about a factor of 5 for a factor of 10 increase in oxygen abundance; second, that the oxygen/sulphur abundance seems constant at 45 + or - 15 from galaxy to galaxy; and third, that the abundance gradient in M31 is -0.05 + or - 0.02 dex/kpc.