Magnetic Activity Study Of Low Mass Late-type Eclipsing Binaries

There are solar-like phenomena in the late-type stars with rapid rotation coupled with thick convective zones,such as star-spots,speckles,flares,prominences,etc.The magnetic field is the key factor of those activities.According to the theory of solar magnetic field generator,the magnetic activity of the sun is caused by the interaction between the external convection,rotation and the differential rotation.In order to extend the solar magnetic field generator theory to the sun-like stars,it is necessary to conduct detailed study on the magnetic activity and its relationships to rotation and other physical parameters of the sunlike stars.Studying the magnetic activities of late-type stars with various physical parameters gives researchers better understanding of the influence of different parameters on this phenomenon,thus a more detailed understanding of stellar magnetic activities.The main results of this dissertation are as follows:·Using 27 sets of multi-band photometry light curves of DV Psc acquired from a long term photometric campaign carried out in the last 10 years using the 1 m-class telescopes and the irst high-resolution spectroscopic data from 7 nights in Jan.2017 using the 2.16 m telecope,we analyzed the physical mechanisms of period variation,star-spot activity,optical lares,and chromospheric activities of DV Psc.There are two active regions of star-spots t longitude belts with periods of 3.60?±0.03?years and 3.42?±0.02?years at about 90^?and 70^?,respectively.Moreover,the magnitude difference of Max.I-Max.II shows cyclic scillation of 5.15?±0.01?years.The updated O-C diagram covering a period of approximately 20 years shows an oscillation in its orbital period.This oscillation might be caused y a third body with its orbital period of 14.58?±0.28?years.During our decade long photoetric campaign,we observed DV Psc for a total of 326.4 hours,detected 21 outbursts with lare energies in the range of?6.62-1106.85?×10²⁴J.The slope of the relationship between he phase of max flare and spots is 0.842?±0.083?,implying a positive correlation between pots and flares.Our high-resolution spectroscopic observations of DV Psc show obvious missions above continuum in the H_?line,and small self-reversal emissions of the Ca ii RT lines.DV Psc shows high level of activities in both photosphere and chromosphere.We revised the absolute parameters of DV Psc and found that the parameters of the two omponents are in good agreement with the 0.050 Gyr tracks of the theoretical model.·We present new BVRI light curves of the short-period W Uma type eclipsing binaries V1101 er and AD Phe from our observations carried out from 2014 to 2015 using SARA KP and ARA CT telescopes.We determined their orbital and star-spot parameters,derived updated ephemerides and found there existed a cyclic variation overlaying a continuous period ncrease?V1101 Her?and decrease?AD Phe?.This kind of cyclic variation may be atributed to the light-time effect via the presence of a third body or magnetic activity cycle.The orbital period increase suggests that V1101 Her is undergoing a mass transfer from the rimary to the secondary component[dM₁/dt=2.64?±0.11?×10^-6M_?/years]with a third ody[P₃=13.9?±1.9?years],or 2.81?±0.07?×10^-6M_?/years for increase and magnetic ycle[12.4?±0.5?years].The long-term period decrease suggests that AD Phe is undergoing a mass transfer from the secondary component to the primary component at a rate of 8.04?±0.09?×10^-8M_?/years for period decrease and a third body[P₃=56.2?±0.8?years],or–-7.11?±0.04?×10^-8M_?/years for decrease and magnetic cycle[50.3?±0.5?years].·We collected the orbital parameters of 208 short-period stars with magnetic cycles by the ethod of obtaining magnetic cycles such as orbital period variations,spot phase migration ariations,brightness variations,etc.We discovered the weak relationship between log-log cale of P_cyc/P_orbrb versus 1/P_orbrb with a slope is 0.711?±0.047?,indicating that the shorter tation period,the shorter magnetic activity cycle may be.We cross-matched the LAM-ST DR6 stellar spectra with the updated catalog of international variable stars index and btained 101572 spectral data for 57905 variable stars,arranged their physical parameters and measured the EW of the spectral lines?H_?,H_?,H_?,H_?,H₈,Ca ii H&K and Ca ii IRT? as stellar chromosphere activity indicator.By statistical analysis of the chromospheric activity of those variable stars,we found that there is a weak relationship between the EW of the chromospheric activity indicator H_?with the period of the variable stars,indicates that the chromospheric activity of short period variable stars are stronger than that of long period ones.