A STUDY OF THE SPATIAL AND SPECTRAL CHARACTERISTICS OF THE CORONA OF AR LACERTAE

X-ray observations of the eclipsing RS CVn binary AR Lac covering both primary and secondary minimum, obtained with the position sensitive proportional counter (PSPC) on-board ROSAT, are presented. The X-ray light curves clearly show a deep primary eclipse in all three PSPC spectral bandpasses covering the bands 0.1-0.28 keV, 0.4-1.1 keV, and 1.1-2.4 keV. A shallow secondary minimum occuring before phase 0.5 is seen in the total fight curve. Phase-dependent spectral analysis is performed both with a two-temperature model as well as a hydrostatic loop model. During primary eclipse the emission measures of the low- and the high-temperature component drop, while the derived coronal temperatures show no orbital variation. The mean temperature values are 3 x 10(6) K and 14 x 10(6) K, respectively; in the context of the hydrostatic loop model, we find peak loop temperatures of approximately 35 x 10(6) K. In order to localize the X-ray emitting regions on the stellar surfaces, a coronal emission region modeling is performed. Two best-fit models are obtained; both models require one prominent coronal feature on each star, a compact structure on the G star (size approximately 0.03 R.), and a more extended structure associated with the K star (size approximately 1-2 R.). No evidence is found for hot plasma pervading the whole binary system, all the coronal structures appear to be associated with the individual binary components. In both models 55(45)% of the total X-ray intensity originate from the K (G) star.