2011PASP..123...34L

We present new multiband CCD photometry for AA UMa made on eight nights between 2009 January and March; the light curves are the first ever compiled. Historical light curves, as well as ours, display partial eclipses and inverse O'Connell effects, with Max I fainter than Max II. Among possible spot models, a cool spot on either of the component stars and its variability with time permit good light-curve representations for the system. A total of 194 eclipse timings over 81 yr, including our five timings, were used for ephemeris computations. We found that the orbital period of the system has varied due to a periodic oscillation overlaid on an upward parabolic variation. The continuous period increase at a fractional rate of is consistent with that calculated from the Wilson & Devinney code and can be interpreted as a thermal mass transfer from the less massive to the more massive secondary star at a rate of. The periodic component is in satisfactory accord with a light-time effect due to an unseen companion with a period of 28.2 yr, a semiamplitude of 0.007 days, and a minimum mass of, but this period variation could also arise from magnetic activity.