Variability of the Rotation Period of the White Dwarf in the Magnetic Cataclysmic Binary System EX Hya

Observations have been made of the two-period magnetic cataclysmic system EX Hya using the RC16 and TOA-150 telescopes at the Tzec Maun Observatory on 6 nights during 2010-2011 (with alternating changeable VR filters). Data from the WASP, ASAS, and AAVSO archives have also been analyzed. The time series were processed using the MCV program. Changes in the rotation period of the white dwarf are analyzed on the basis of our own and previously published data on the times of the maxima. An ephemeris is obtained for the maximum radiative fluxes associated with the rotation of the magnetic white dwarf, T (max) =2437699.89079(59) + 0.0465464808(69)a (TM) E -aEuro parts per thousand 6.3(2) a (TM) 10(-13) E (2), which corresponds to a characteristic time scale of 4.67(12) center dot 10(6) years for the rotation spin-up. This value conflicts with the estimated mass of the white dwarf, 0.42 M (aEuro), derived from X-ray observations by Yuasa, et al. (2010), but is consistent with the estimated masses 0.79 M (aEuro) (white dwarf) and 0.108 M (aEuro) (red dwarf) obtained earlier by Beuermann and Reinsch (2008) and the assumption that capture of an accretion plasma by the magnetic field of the white dwarf is taking place near the boundary of the Roche lobe. The analyzed times of the minima do not support the assumption by Mauche, et al. (2009), of a statistically significant cubic term in the ephemeris. Despite the occurrence of outbursts in EX Hya, there are substantial differences from DO Dra, which supports the inclusion of the corresponding groups "outbursting intermediate polars" and "magnetic dwarf novae" in the detailed classification of intermediate polars.