Period variation and four color light curves investigation of AB And

New determined B, V, R and I light curves of AB And have been analyzed by the fourth version of the Wilson-Devinney code. This is the first time to obtain four color light curves of AB And simultaneously. It is found that AB And is a middle mass ratio W-type contact binary system with a degree of contact factor f=25.2%±0.2%. One dark spot on the primary component is introduced to explain the unequal height of the two maxima. The orbital period investigation based on all the visual, photographic, photoelectric and CCD times of light minimum shows that the period of AB And includes a long-term increase (dP/dt=1.46×10^-7 days yr) and an oscillation (A₃=0.121 days; T₃=98.3 years). These may be caused by mass transfer and the light time effect of a third compact companion.