| Contract binaries with W UMa type are short-period eclipsing systems.Their components process a common convective envelope,resulting in that the temperature difference between components is not large.Modeling variations by WD program is the main approach for determining physical parameters of eclipsing binaries.It is generally accepted that such binaries are formed from initial detached binaries via angular momentum loss due to magnetic torques caused by stellar winds,and eventually coalesce into fast rotating single stars or blue stragglers.Therefore,the analysis on contact binaries will be very meaningful for realizing stellar resolution.Observed brightness,spectrum and radial velocity changes can limit the geometric configuration of a system.Since 2016 to 2017,we had done photometry observation on short-period contact binaries VZ Lib,VZ Psc and FG Sct by the SARA CT at the Cerro Tololo Inter-American Observatory,Holcomb Telescope at Bulter University and the 60-cm Telescope at Xinglong Station of the National Astronomical Observatory of China.Correspondingly,we gained two,four and two light-curves respectively.Simultaneously,we derived two spectrum of VZ Psc by LAMOST and the 2.4-m Telescope at Yunnan Observatory of Chinese Academy of Science.Finally,we respectively determined orbital parameters?including the effective temperature and mass of primary and secondary component,mass ratio?,and analyzed the orbital variation and corresponding physical mechanisms.For VZ Lib,we derived 5 light curve minimum times,and analyzed its period variation.The O-C reveals a potential cyclic orbital period variation.By analysis,the period variation could be attributed to either the light-time effect due to a tertiary component or magnetic activity cycle mechanism.We derived the periods of the tertiary component of VZ Lib to be 48.7?±0.1?years or magnetic cycle to be 46.9?±1.9?years.For VZ Psc,we derived 7 light curve minimum times and obtained its physical parameters.After analyzing its orbital period,our result was different from pervious works and didn't find obvious orbital period variation.At the same time,we proved that there is indeed peculiar phenomenon in VZ Psc that high fillout factor and high temperature difference between components simultaneously existing.Making use of spectral subtraction method,we found that the spectrum of VZ Psc show strong emission lines of Ca II H+K,H?,H?,H?and Ca II IRT,which imply strong chromospheric activities.For FG Sct,we derived 4 light curve minimum times and firstly determined its orbital parameters.The O-C curve of FG Sct shows a downward parabolic trend.And we found its orbital period had a declining inclination of 6.39?±0.24?×10-8 days/year,which was likely caused by mass transfer from the secondary component to the primary component or angular momentum loss due to magnetic stellar wind.At present,the studies on contact binaries is mainly in optical band and will be extended to the radio band in the future.At the same time,we need to make effective use of LAMOST data,Kepler Space Telescope data and TESS?Transiting Exoplanet Survey Satellite?data just released. |
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