Studies on the Equatorial Spot of G-type Contact Binary UV Lyn

Abstract

Abstract New CCD photometric observations of G-type contact binary UV Lyn were obtained in 2006 and 2020, when the light curves (LCs) showed positive O’Connell effect and negative O’Connell effect, respectively. From the previous studies, the LCs by other ground-based telescope are variable from 1973 to 2020, particularly the magnitude difference between the two maxima. These phenomena indicate that the component has been active in the past 47 yr. In addition, during monitoring by the space telescope Transiting Exoplanet Survey Satellite (TESS) from January to March 2020, we fortunately found continuous variations from the O’Connell effect in every cycle for the first time. The analysis also shows that in a short time, the positive O’Connell effect has been transformed into the negative one, which demonstrates that there are stronger magnetic activities on the surface of the component. By using the Wilson-Devinney code with a spot model, these photometric solutions confirm UV Lyn is a shallow W-subtype contact binary with a cool equatorial spot on the less massive component. The successive variability of the O’Connell effect possibly results from one equatorial cool spot shifting gradually along with time. We also investigated its O − C curve from these continuous LCs, and there is no apparent variation in such a short time. However, regarding the O’Connell effect as the indicator of magnetic activity indicates the system is possibly undergoing a periodic trend with a period of nearly 38 days. Comparing with the trend of the O − C curve, we could not find any relation between the period variation and magnetic activity.