Orbital Solutions and Absolute Elements of the W UMa Binary MW Pavonis

We present differential $UBV$ photoelectric photometry obtained by Williamon of the short-period A-type W~UMa binary MW~Pav. With the Wilson-Devinney analysis program we obtained a simultaneous solution of these observations with the $UBV$ photometry of Lapasset (1977,1980), the $V$ measurements by the $ASAS$ program, and the double-lined radial velocity measurements of Rucinski & Duerbeck (2006). Our solution indicates that MW~Pav is in an overcontact state, where both components exceed their critical Roche lobes. We derive masses of $M_1 = 1.514 \pm 0.063 \, M_\sun$ and $M_2 = 0.327 \pm 0.014 \, M_\sun$, and equal-volume radii of $R_1 = 2.412 \pm 0.034 \, R_\sun$ and $R_2 = 1.277 \pm 0.019 \, R_\sun$ for the primary and secondary, respectively. The system is assumed to have a circular orbit and is seen at an inclination of $86.39\arcdeg \pm 0.63\arcdeg$. The effective temperature of the primary was held fixed at $6900$~K, whereas the secondary's temperature was found to be $6969 \pm 10$~K. The asymmetry of the light curves requires a large, single star spot on the smaller, less massive secondary component. A consistent base solution, with different spot characteristics for the Williamon, Lapasset, and $ASAS$ data, was found. The modeled spot varied little during the 40-year range of photometric observations. The combined solution utilized a third light component and found that the period is changing at a rate of dP/dt~=~$(6.50 \pm 0.19) \times 10^{-10}$.