Spectral imaging maps of AR Lacertae I. Results from IUE observations in 1994 October

In October 1994 the RS CVn eclipsing binary AR Lacertae was monitored by IU E during tao orbital cycles. We have used 59 low resolution spectra, acquir ed in the range 1150-1950 Angstrom, to derive light curves for emission lin es formed at different temperatures between about 10 000 and 200 000 K and to study the flare signatures versus temperature of line formation. We have analyzed a sequence of 59 high resolution Mg II k line profiles using mult i-Gaussian fits (the spectral imaging technique) to derive information of t he spatial structure of the chromospheres of both stars in the AR Lac syste m. We discuss the quiet chromospheric emission from both stars, and we show that enhanced Mg II emission is present in extended structures corotating with the KO SV star and close to the system center-of-mass. We also report on evidence for absorbing structures toward both the stars. This study of A R Lac used the new orbital elements of Marine et al. (1998) and spectra red uced and calibrated with NEWSIPS. A comparison between fluxes derived from the analyzed NEWSIPS spectra and from IUESIPS spectra is provided.