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2000ApJ...539..687O - Astrophys. J., 539, 687-705 (2000/August-3)
Calibration of nebular emission-line diagnostics. II. Abundances.
OEY M.S. and SHIELDS J.C.
Abstract (from CDS):
Our data agree well with both the modeled R23 and S23 abundance diagnostics for O and S. We present the first theoretical tracks for S23, which are in excellent agreement with a larger available data set. However, contrary to earlier suggestions, S23 is much more sensitive to the ionization parameter (U) than is R23. This occurs because S23 does not sample S IV, which is often a significant population. We therefore introduce S234≡([S II]+[S III]+[S IV])/Hβ and demonstrate that it is virtually independent of U. Predicted and observed spatial variations in S234 are thus dramatically decreased in contrast to S23. The intensity of [S IV] 10.5 µm can be easily estimated from the simple correspondence between [S IV]/[S III] and [O III]/[O II]. Using this method to estimate S234 for data in the literature yields excellent agreement with our model tracks, hence we give a theoretical calibration for S234. Our models show that the double-valued structure of S23 and S234 remains an important problem as for R23, and, at present, we consider calibrations of these S diagnostics reliable only at Z≲0.5Z☉. However, the slightly larger dynamic range and excellent compatibility with theoretical predictions suggest the S parameters to be more effective abundance diagnostics than R23.
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Journal keyword(s): Galaxies: Abundances - Galaxies: ISM - ISM: H II Regions - ISM: Abundances - Galaxies: Magellanic Clouds - ISM: Supernova Remnants
Simbad objects: 12
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