2008AJ....136..337Z

The first complete multi-color CCD photometric light curves of the eclipsing binary AS Ser were obtained over three nights in 2005. Using the latest Wilson-Devinney (WD) code, we computed the photometric elements of this system. It turns out that AS Ser is a near-contact binary system with both components filling more than 99% of their Roche lobes. It belongs to a marginal contact binary system within the parameter uncertainties. The marginal characteristic of AS Ser reveals that this target may be in a rare phase predicted by the thermal relaxation oscillation (TRO) theory. The asymmetry of the light curves can be explained by a dark spot on the secondary component, which is consistent with its late-type nature. Combining all available times of light minimum, we derived a new orbital period of AS Ser and found a periodic oscillation varying within an amplitude of 0.0049 days and a period of 11.8 years. This period change may be the result of the light-time effect due to a presumed tertiary component (M₃> 0.28M_☉) or might result from magnetic activity cycles of the two components.