CORONA(E) OF AR LACERTAE .1. THE TEMPERATURE AND ABUNDANCE DISTRIBUTION

X-ray spectra of the RS CVn binary AR Lac, obtained from simultaneous observations with the ROSAT PSPC and the ASCA SIS and GIS detectors, h ave been analyzed to study the coronal temperature and abundance distr ibution. The spectra were jointly fitted with plasma emission models t o the following possible temperature distributions: (a) one with discr ete multitemperature emission components, (b) a continuous emission me asure with a power-law dependence on temperature, and (c) a continuous emission distribution parameterized by the sum of a sixth-order Cheby shev polynomial. We find that (i) solar abundance plasma models with e ither discrete or continuous emission measure (GEM) distributions are rejected, (ii) the best fit is obtained with a two-temperature (2T) pl asma emission model with an underabundance of the elements O, Mg, Si, S, Ar, Ca, and Fe by a factor of 3-4 relative to the solar photospheri c values, and (iii) the best-fit CEM distribution also has similarly r educed abundances but fits the data less well than the 2T model. These results are confirmed even when the Fe-L region, which is subject to uncertainties in the atomic physics, is excluded from the fit. We cons ider optical depth effects as unlikely to be the explanation for the o bserved weakness of the line complexes relative to the continuum. Anal ysis of the spectral data during the primary and secondary eclipses sh ows that the emission measure of the high-temperature component in the 2T models appears to be more affected by the primary eclipse than the low-temperature component, suggesting that part of the former is conc entrated in structures that are spatially more compact.