Abstract
In this paper, new determined \(BVR_{c}I_{c}\) light curves and radial velocities of V781 Tau are presented. By analyzing the light curves and radial velocities simultaneously, we found that V781 Tau is a W-subtype medium contact binary star with a mass ratio of \(q=2.207\pm0.005\) and a contact degree of \(f=21.6(\pm1.0)~\%\). The difference between the two light maxima was explained by a dark spot on the less massive primary component. The change of the orbital period of V781 Tau was also investigated. A secular decrease at a rate of \(-6.01(\pm2.28)\times 10^{-8}~\mbox{d}/\mbox{yr}\) and a cyclic modulation with a period of \(44.8 \pm 5.7~\mbox{yr}\) and an amplitude of \(0.0064\pm0.0011~\mbox{day}\) were discovered. The continuous period decrease may be caused by angular momentum loss due to a magnetic stellar wind. The Applegate mechanism failed to explain the cyclic modulation. It is highly possible that the cyclic oscillation is the result of the light travel time effect by a third companion.
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IRAF is distributed by the National Optical Astronomy Observatories, which are operated by the Association of Universities for Research in Astronomy under cooperative agreement with the National Science Foundation.
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Acknowledgements
This work is partly supported by the National Natural Science Foundation of China (Nos. 11203016, U1431105), by the Natural Science Foundation of Shandong Province (No. ZR2014AQ019), and by the Open Research Program of Key Laboratory for the Structure and Evolution of Celestial Objects (No. OP201303). We thank the anonymous referee very much for her/his help, constructive comments, and suggestions, which helped to improve this paper.
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Li, K., Gao, DY., Hu, SM. et al. The active W UMa type binary star V781 Tau revisited. Astrophys Space Sci 361, 63 (2016). https://doi.org/10.1007/s10509-016-2649-8
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DOI: https://doi.org/10.1007/s10509-016-2649-8