Orbital parameters and period variation studies of the short-period eclipsing binaries FG Sct, VZ Lib and VZ Psc

Abstract

We present eight sets of new light curves for binaries FG Sct, VZ Lib and VZ Psc, which are all contact eclipsing binaries with short orbital periods. We carried out our observations from 2016 to 2017 using the 60-cm telescope administered by National Astronomical Observatories, Chinese Academy of Sciences, the Holcomb Observatory at Butler University and the SARA-CT telescope in Chile. We firstly determined the orbital parameters of FG Sct using the O − C method and obtained photometric solutions utilizing the updated W-D program. We also studied its period variation and discovered that its orbital period is decreasing at a rate of 6.39(±0.24) × 10−8 d yr−1, which was likely caused by mass transfer from the primary component to the secondary component or angular momentum interchange between the two components via magnetic interactions. For VZ Lib and VZ Psc, we simultaneously analyzed their BV RI light curves in conjunction with the published radial velocities. In order to obtain the orbital parameters of VZ Lib, we also analyzed its period variation and revised cyclic change, which could be attributed to either the light-time effect due to a tertiary companion or magnetic activity cycle mechanism. We derived the periods of the tertiary component of VZ Lib to be 48.7(±0.1) yr or magnetic cycle to be 46.9(±1.9) yr. Strong emission lines at Ca ii H+K, Hα, Hβ, Hγ and Ca ii IRT were detected in the LAMOST spectra of VZ Psc, which imply chromospheric activities in this binary system.