AD Cancri: A Contact Binary with Components in Poor Thermal Contact

Abstract

We present the light curve and photometric solutions of the contact binary AD Cnc. The light curve appears to exhibit a typical O' Connell effect, with Maximum I brighter than Maximum II by 0.010 mag. in V. From 1987 to 2000, the light curve showed changes of shape: the depth of the primary eclipse increased by about 0.056(m) while that of the secondary eclipse decreased by about 0.032(m), so the difference between the primary and the secondary eclipses increased by about 0.088(m), while there was no obvious variation in the O' Connell effect. Using the present and past times of minimum light, the changes in the orbital period of the system are analyzed. The result reveals that the orbital period of AD Cnc has continuously increased at a rate of (dt)/(dp) = 4.4 x 10(-7) day yr(-1). The light curve is analyzed by means of the latest version of the Wilson-Devinney code. The results show that AD Cnc is a W-subtype contact binary with a small mass ratio of 0.267 and the two components are in poor thermal contact. AD Cnc has a component temperature difference exceeding 500 K, and exhibits a shallow contact of 3.6%. The asymmetry of the light curves is explained by the star spot model.