A CCD Photometric Study of the W UMa–Type Binary System EZ Hydrae

Abstract

New complete CCD light curves in B and V bands for EZ Hya are presented in this paper. The first photometric spectroscopic solution for this system was obtained by using the latest version of the Wilson‐Devinney program. The orbital inclination of 83 3(±0 6) confirms that this system is a total eclipsing binary system. Our solution indicates that EZ Hya is W‐type overcontact binary with a small mass ratio of q = 0.257(±0.001) and an overcontact degree of f = 34.2%. Combining our light curves with the radial velocity curves from King & Hilditch, we were able to give the absolute parameters of this system: a = 2.98(±0.61) R⊙, R1 = 1.54(±0.32) R⊙, R2 = 0.85(±0.18) R⊙, M1 = 1.37(±0.12) M⊙, and M2 = 0.35(±0.03) M⊙. A period analysis using all photoelectric and CCD times of minimum light suggests an oscillation period of 30.9(±0.61) yr and an amplitude of 0.0185(±0.0012) days. The sinusoidal change can be explained either by the presence of an unseen third body or as the result of magnetic activity cycles of both components.