Magnetic activity on two contact binaries: VW Boo and V1128 Tau from TESS data

Abstract

Using the continuous TESS data, we found small intrinsic variations in the light curves of VW Boo and V1128 Tau. We selected five sets of light curves and derived the photometric solutions by using the Wilson-Devinney code. The results indicate that the intrinsic light curve variations in VW Boo are attributed to the evolution of a cool spot. In the case of V1128 Tau, the disappearance or reappearance of a cool spot might account for the variation in three sets of light curves. The obtained solutions also reveal that these two systems are W-type shallow-contact binaries (f≤15%). Period analyses for these two systems were carried out based on all available times of minimum. The period analysis of VW Boo shows that its period is decreasing at a rate of dP/dt=−1.52×10−7d yr−1, together with a cyclic oscillation with a period of 27.17 yr and a semi-amplitude of 0.0063 d. Similarly, the orbital period of V1128 Tau also shows a secular decrease (dP/dt=−1.40×10−7d yr−1), accompanied by a cyclic oscillation (P3= 16.11 yr and K3=0.0011 d). The secular decrease might be caused by mass transfer, while the cyclic oscillation might result from the presence of a third body or magnetic activity.