  We observed the coronally active eclipsing binary, AR Lac, with the High
Energy Transmission Grating on Chandra for a total of 97 ks, spaced over five
orbits, at quadratures and conjunctions. Contemporaneous and simultaneous EUV
spectra and photometry were also obtained with the Extreme Ultraviolet
Explorer. Significant variability in both X-ray and EUV fluxes were observed,
dominated by at least one X-ray flare and one EUV flare. We saw no evidence of
primary or secondary eclipses. X-ray flux modulation was largest at high
temperature, indicative of flare heating of coronal plasma. Line widths
interpreted in terms of Doppler broadening suggest that both binary stellar
components are active. From line fluxes obtained from total integrated spectra,
we have modeled the emission measure and abundance distributions. A strong
maximum was found in the differential emission measure, characterized by peaks
at log T = 6.9 and 7.4, together with a weak but significant cooler maximum
near log T=6.2, and a moderately strong hot tail from log T= 7.6-8.2. Coronal
abundances have a broad distribution and show no simple correlation with first
ionization potential. While the resulting model spectrum generally agrees very
well with the observed spectrum, there are some significant discrepancies,
especially among the many Fe L-lines. Both the emission measure and abundance
distributions are qualitatively similar to prior determinations from other
X-ray and ultraviolet spectra, indicating some long-term stability in the
overall coronal structure.
