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 IUE during two orbital cycles. We have used 59 low resolution spectra, acquired in the range 1150-1950 Å, to derive light curves for emission lines 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 MgII k line profiles using multi-Gaussian fits (the spectral imaging technique) to derive information of the spatial structure of the chromospheres of both stars in the AR Lac system. We discuss the quiet chromospheric emission from both stars, and we show that enhanced MgII emission is present in extended structures corotating with the K0 IV star and close to the system center-of-mass. We also report on evidence for absorbing structures toward both the stars. This study of AR Lac used the new orbital elements of Marino et al. (1998) and spectra reduced and calibrated with NEWSIPS. A comparison between fluxes derived from the analyzed NEWSIPS spectra and from IUESIPS spectra is provided.