Multi-color photometric investigation of the totally eclipsing binary NO Camelopardalis.

Multi-color photometric light curves of NO Camelopardalis in V, RC, and IC bands are obtained and analyzed simultaneously using the Wilson-Devinney program. The solutions suggest that NO Cam is an A-subtype overcontact binary with a mass ratio of q = 0.439 and a contact degree of f = 55.5%. The small temperature difference (ΔT = 44 K) between its two components indicates that the system is under thermal contact. The high orbital inclination (i = 84.° 5) strengthens our confidence in the parameters determined from the light curves. All available times of minimum light are collected and period variations are analyzed for the first time. The O - C curve reveals that its period is increasing continuously at a rate of dP/dt = +1.46 × 10-9, which can be explained by mass transfer from the less massive component to the more massive one. After the upward parabolic variation is subtracted, the residuals suggest that there may be a cyclic variation with a period of 2.23 yr and an amplitude of A3 = 0.00153 d, which may due to the light-traveltime effect arising from the gravitational influence of a close-in tertiary component. The close-in companion reveals that early dynamic interaction among a triple system may have played a very important role in the formation of the WUMa-type binaries. [ABSTRACT FROM AUTHOR]