Henry and Fekel are determining the rotational periods and light amplitudes. They will combine the photometric results with existing spectroscopic results to identify the single and binary stars in the sample and, where possible, to check for synchronous, pseudosynchronous, or asynchronous rotation of the binary stars. This star is difficult to observe at a single site because of its 3.96-day period. Henry has reprogrammed the telescope during the 1994 summer shutdown to make the additional sky background measurements to reduce or eliminate this problem. As part of this program, he has begun a period analysis of the 30-inch data to determine which stars show rotational modulation of brightness due to individual active regions.
Preliminary results suggest rotational modulation on at least several stars.
This should result in a paper detailing the 10-year brightness variations of these stars. Eaton has continued his analyses of zeta Aurigae binaries as probes of stellar chromospheres and winds. During the period of this report, he published analyses of IUE observations of 31 Cyg away from atmospheric eclipses and of AL Vel in an abnormally strong atmospheric eclipse. In addition, they obtained violet data from NSO at a few critical phases to measure strengths of Balmer lines and a few metallic lines. These spectra constitute the most extensive, probably the best, data set yet obtained for a zeta Aur binary, and they allow mass column densities through the wind and chromosphere to be measured accurately from the strength of Ly-alpha absorption.