EXTREME-ULTRAVIOLET EXPLORER INVESTIGATION OF 3 SHORT-PERIOD BINARY STARS

Extreme Ultraviolet Explorer spectroscopic observations (SW, MW, and L W bands, covering 80-160, 170-350, and 300-450 Angstrom with resolutio ns 0.5, 1, and 2 Angstrom respectively) and photometric observations ( Deep Sky Survey [DSS], broadband 70-140 Angstrom) have been obtained f or two contact binaries, 44i Boo B and VW Cep, and one close but detac hed binary, ER Vul. All three systems have orbital periods shorter tha n 1 day and thus are expected to show ''saturated'' levels of chromosp heric, transition region, and lower corona emissions. Only moderate fl aring activity was seen in the DSS light curves of all three stars. Th e phased DSS light curve of 44i Boo B shows one minimum at the eclipse of the hotter, smaller component, while the phased light curve of ER Vul has a slightly higher level at the first maximum, following the de eper eclipse. An unsuccessful attempt has been made to determine the t emperature dependence of the differential emission measure (DEM) of th e coronal plasma for 44i Boo B on the basis of iron ion emission lines . It utilized the singular value decomposition formalism developed by Schmitt et al. to handle the inverse problem of the spectrum-to-DEM ma pping. Implementation of this formalism suffered from the low number o f available spectral features and possibly also inconsistencies in the line strengths, which become amplified in the mathematical inversion process. However, experiments with the direct reconstruction of the sp ectra, which were generated with the DEM functions available from the literature, favor the distribution of Dupree et al. in preference to t he two-temperature model of McGale et al. A comparison of the relative line fluxes f(line)/f(bol) for selected strongest chromospheric, tran sition region, and low-corona emission lines in 44i Boo B, VW Cep, ER Vul, and the single, rapidly rotating star AB Dor shows that the curre ntly available data are consistent with the period-independent (''satu rated'') levels of activity for features forming at log T less than or equal to 5 in all four stars, while features formed at log T similar or equal to 6.8-7.1 are definitely the weakest in AB Dor.