UPDATED PHOTOMETRY AND ORBITAL PERIOD ANALYSIS FOR THE POLAR AM HERCULIS ON THE UPPER EDGE OF THE PERIOD GAP

Twenty-one new optical light curves, including five curves obtained in 2009 and sixteen curves detected from the AAVSO International Database spanning from 1977 to 2011, demonstrate 16 new primary minimum light times in the high state. Furthermore, seven newly found low-state transient events from 2006 to 2009 were discovered, consisting of five Gaussian-shaped events and two events with an exponential form with decay timescales of > tau((R) over dot2), which is required by numerical calculations of the secular evolution of cataclysmic variables. In order to explain the prominent periodic modulation, three plausible mechanisms-spot motion, the light travel-time effect, and magnetic active cycles-are discussed in detail.