A PHOTOMETRIC-STUDY OF THE VERY SHORT-PERIOD ECLIPSING BINARY EH HYDRAE

Recent Johnson-Cousins' B,V,R(c),I(c) photoelectric observations of the very short period W UMa variable, EH Hya are presented. These observations were made, using the Yale 1M telescope and the dry-ice-cooled Hamamatsu Ga-As PMT at Cerro Tololo Inter-American Observatory. The light curves reveal that the eclipses are total, and that the primary eclipse is an occultation. Thus, the system is of W-type, with the larger component being the cooler. Standard magnitudes were determined and a reddening estimate was made. A simultaneous solution of the B,V,R light curves was computed using the Wilson-Devinney synthetic light curve code. The solution indicates that the system consists of two late G-type stars in shallow contact with a fill-out factor of 12%. The difference in component temperatures is 336(8) K and the mass ratio is rather extreme, being 0.314(2). EH Hya is compared to other very short period binaries of late G-type and they are found to comprise a fairly homogeneous group with regards to mass ratios, degree of thermal contact, and magnetic activity. Recent results of contact binary observations are discussed along with their relationship to this group and their impact on our understanding of the dynamic structure of contact binaries.