The Observations And Studies On Short-period Red Dwarf Binaries

Generally,the red dwarf binaries belong to close binary systems,which are consisting of two late-type main sequence stars,and their components are always K or M type stars,with a mass less than 0.8 solar mass and effective temperature ranges from 2500 K to 5000 K.The red dwarf is one of most members in our universe,the main feature of them are long main sequence phase,strong magnetic activity and difficult observations etc.Through the study of these red dwarf binaries,we can detach the mechanism of how that short period contact binaries are formed and limit the theoretical model by the obtained results.Recently,as the development of some sky survey,a lot of red dwarf binary candidates are found.We studied some of them by photometry in detail and obtained corresponding results as follows:1.The preliminary photometric solutions are derived by using the 2013 ver-sion of the Wilson–Devinney?W–D?code.The photometric solutions suggest that1SWASP J200503.05-343726.5 is a shallow-contact eclipsing binary?f=9.0%?with a mass ratio about 1.0 near the period limit,it is also in geometrical contact.The main reason of so high mass ratio could be that these W UMa type close binaries are little evolved whose primaries have a mean densities close to those zero-age main sequence stars.Just because of this,they formed contact binary system with a high initial mass ratio at least 0.7.The distortion of the light curves are also discovered,which can be explained by the presence of one cool-spot in the primary components due to its magnetic activity.Based on all collected eclipse times,the orbital pe-riod change was analyzed.It is suggested that the orbital period of the 1SWASP J200503.05-343726.5 shows an increase at a rate of dP/dt=5.43×10^-8days yr^-1.The period increase may be caused by mass transfer from the less massive compo-nent to the more massive one.This shallow-contact system may be formed from a detached short-period binary via orbital shrinkage because of dynamical interactions with a third component or by magnetic braking.2.The CCD photometric light curves for the short-period eclipsing binary 1SWASP J140533.33+114639.1?hereafter J1405?in the BV R bands are presented and ana-lyzed using the 2013 version of the Wilson-Devinney?W-D?code.It is discovered that the J1405 is a W-subtype shallow contact binary with a contact degree of f=7.9±0.5%and a mass ratio of q=1.55±0.02.In order to explain the asym-metric light curves of the system,a cool star-spot on the more massive component was employed.This shallow contact eclipsing binary may be formed from a short-period detached system through the orbital shrinkage due to angular momentum loss.Based on?O-C?method,the variation of the orbital period was studied using all the available times of the minimum light.The?O-C?diagram reveals that the period is increasing continuously at a rate of dP/dt=+2.09×10^-7days yr^-1,which can be explained by mass transfer from the less massive component to the more massive one.3.First multi-wavelength photometric light curves?LCs?of the short-period eclipsing binaries?EBs?1SWASP J224747.20-351849.3 and 1SWASP J034439.97+030425.5are presented and analyzed using the 2013 version of the Wilson-Devinney method.In order to explain the asymmetric LCs of 1SWASP J034439.97+030425.5,a cool star-spot on the less massive component was employed.It is discovered that both of them are possible triple-system with obvious third light detected in our analysis,the average luminosity contribution of the tertiary component to the total light is49.78%,67.89%for J0344 and J2247,respectively.At the same time,all of them are W-subtype contact EBs.The contact degree and mass ratio are f=4.9±3.0%,q=2.456±0.013 for J034439.97+030425.5,f=30.9±10.8%,q=1.204±0.040for 1SWASP J224747.20-351849.3,respectively.According to the?O-C?method,the variations of the orbital period were studied using all the available times of the minimum light.The?O-C?diagrams reveal parabolic changes of their orbital period,which can be explained by the mass transfer between two components of the system.Another interpretation is that it maybe only a part of long-time period cyclic variation caused by the presence of a third body.The third body may play an important role in the formation and evolution of these short-period binary systems by drawing angular momentum from the central system.4.In this paper,we presented four-color?BV R_cI_c?photometric light curves?LCs?for the two similar low-mass detached binaries NSVS 11868841 and GJ 3236.These LCs were analyzed using the 2013 version of the Wilson-Devinney?W-D?code with cool star-spots.It revealed that both of them were active at present,and the cool star-spots'evolution were discussed by comparing different photometric solutions in different seasons.Besides,a total of 5 flare events confirmed for GJ 3236in our observations?about 20 hours?,which revealed a high flare rate about 0.025flares per hour.According to all available times of the light minimum,we analyzed the variations of orbital period using the?O-C?method.A short-time oscillation of NSVS 11868841 about 1.76 years exhibited in its?O-C?diagram,in contrast,for GJ 3236,similar change was not found.Based on our research results and published statistical studies about?O-C?cycle oscillation,we supported the conclusion that short-time periodical variations of orbital period between 1-7 years for EA-type eclipsing binaries?EBs?were possible caused by the tertiary components,and Applegate mechanism need much longer time to work for these active late-type detached EBs.5.New photometric observations of NSVS 01286630 were performed and ob-tained two sets of four-color?B,V,R_c,I_c?light curves?LCs?.Using the 2013version of the Wilson-Devinney?W-D?code,we analyzed these data.The photo-metric solutions reveal that NSVS 01286630 is an active detached eclipsing binary?EB?with a high orbit inclination?nearly 90^??.Remarkably,the value of mass ratio q for NSVS 0128663 is more than 1,but,the effective temperature of the more massive component is lower than the less massive one,which offers an important evidence that the surface of the secondary component of NSVS 01286630 is covered with big cool-star-spots.Besides,star-spots activity is also discussed according to the dynamo mechanism.Based on our new CCD mid-eclipse times and the data published until now,the variation of orbital period were analyzed in detail using a weighted least-squares method.Finally,a cycle oscillation about 3.61 years is dis-covered due to the light-travel time effect?LTTE?,which means the presence of a third body.By means of the minimum mass of this third component we estimated M_3min=0.1 M_?.The third body may affect the orbital evolution of the central binary system by transferring the angular momentum.6.The multi-color?V,R,R_c,I,I_c,W?light curves?LCs?for ultrashort-period?less than 0.2 days?eclipsing binary?EB?2MASS J11553339+3544399?hereafter J1155?are presented and analyzed using the 2013 version of the Wilson-Devinney code.It is discovered that J1155 is a rare detached M-M dwarf EB system with a mass ratio of 0.93,the primary?more massive and hotter?and secondary components are filling 90%and 84.8%of their critical Roche lobes,respectively.It maybe formed from the wider orbits via angular momentum loss?AML?due to magnetic braking and spin-orbit synchronization.Based on the empirical mass-radius relation,the masses and radii calculated for the components of J1155 are M₁=0.475±0.035M_?,M₂=0.441±0.044 M_?,R₁=0.516±0.089 R_?and R₂=0.491±0.105 R_?.By means of the collected light minima times,the orbital period changes of the system were investigated for the first time.The observed-calculated?O-C?diagram shows a cyclic oscillation with an amplitude of 0.00315 days and a period about 9.51 years,which is likely to be due to the light-travel time effect?LTTE?caused by the presence of a third body with a mass of M₃sin?i^???0.125 M_?.The distance of this tertiary component to the mass center of the triple system is about 3.96 AU,and it may play an important role in the early evolution of J1155 by drawing angular momentum from the central system.After BW03 V38 and GSC 2314-0530,our research found another key target in the special evolutional phase.This new discovery offers an important sample to study the formation,evolution and magnetic activity of M-M dwarf EBs.