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We present the analysis of PSPC X-ray observations for a sample of 18 early-type (E and S0) galaxies observed with the ROSAT PSPC. We extracted x-ray spectra for each galaxy both over an extended region containing most of the x-ray flux and, for the more luminous galaxies, in annular regions. Although the emission is sharply peaked toward the galaxy center, due to the possibility of strong radiative cooling in the central region as well as the possible presence of a nuclear source, we investigated, when feasible, the change in the spectral parameters found when fitting the emission from the entire galaxy and by omitting the central region when extracting the spectrum. In modelling the x-ray spectra, we used a Raymond thermal spectrum and allowed the gas temperature and the hydrogen absorption, as well as the heavy element abundances, to be free parameters. In our spectral analysis, we varied all the elements heavier than helium simultaneously. However, the emission lines of iron dominate the spectrum at temperatures around 1~keV, which is appropriate for early-type galaxies. Hence, with the spectral resolution available with the PSPC, the measured constraint is essentially only for iron.
In general, we find that the more X-ray luminous, hotter galaxies have iron abundances at about solar, while the less luminous cooler galaxies have lower abundances. We compare our results to recent ASCA abundance measurements and to measurements of larger systems, groups and clusters, containing significant quantities of hot gas. Finally, we discuss possible explanations for the observed correlation and discuss correlations of the measured iron abundance with other galaxy parameters.
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