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

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 83.3d(+/-0.6d) 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_solar, R₁=1.54(+/-0.32) R_solar, R₂=0.85(+/-0.18) R_solar, M₁=1.37(+/-0.12) M_solar, and M₂=0.35(+/-0.03) M_solar. 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.