Magnetic Activity and Period Variation Studies of the Four W Uma-type Eclipsing Binaries: UV Lyn, V781 Tau, NSVS 4484038, and 2MASS J15471055+5302107

Abstract

Abstract We present new photometric data and LAMOST spectra for the W UMa binaries UV Lyn, V781 Tau, NSVS 4484038, and 2MASS J15471055+5302107. The orbital and starspot parameters are obtained using the Wilson–Devinney program. Comparing the starspot parameters at different times, there are magnetic activities in these four binaries. The orbital period of UV Lyn is increasing at a rate of dP/dt = +8.9(5) × 10−8 days yr−1, which maybe due to mass transfer from the less massive component to the more massive component (dM 1/dt = −6.4 × 10−8 M ⊙ yr−1). The period variation of 2MASS J15471055+5302107 is also increasing at a rate of 6.0(4) × 10−7 days yr−1, which can be explained by mass transfer from the less massive component to the more massive component (dM 1/dt = −2.8 × 10−7 M ⊙ yr−1). The period variation of V781 Tau presents the downward parabola superimposed the cyclic oscillation. The period of V781 Tau is decreasing (dP/dt = −3.2(4) × 10−8 days yr−1), which can be explained by mass transfer from the more massive component to the less massive component (dM 2/dt = −2.2 × 10−8 M ⊙ yr−1). The cyclic oscillation may be due to the magnetic activity with a period of 30.8(5) yr rather than a third body. The period variation of NSVS 4484038 also shows the cyclic oscillation, which could be explained by the magnetic activity with 10.8(1) yr or a black hole candidate. Interestingly, there is a depth variation between the light minimum times of NSVS 4484038, which may also be caused by stellar magnetic activity.