Periodic Variation Studies of the Two Short Period W UMa-type Eclipsing Binaries: LX Lyn and V0853 Aur

In this paper,new light curves(LCs) of contact eclipsing binary(CEB) systems LX Lyn and V0853 Aur are presented and analyzed by using the 2015 version of the Wilson-Devinney(W-D) code.In order to explain their asymmetric LCs,cool starspots on the components were employed.It is suggested that their fill-out degrees are f=12.0%(LX Lyn) and f=26.3%(V0853 Aur).At the same time,we found that LX Lyn is a W-type eclipsing binary(EB) with an orbital inclination of i=84°.88 and a mass ratio of q=2.31.V0853 Aur is also a W-type CEB with a mass ratio of q=2.77 and an orbital inclination of i= 79°.26.Based on all available times of light minimum,their orbital period changes are studied by using the O-C method.The O-C diagram of LX Lyn reveals a cyclic oscillation with a period of about 14.84 yr and an amplitude of 0.0019 days,which can be explained by the light-travel time effect(LTTE) due to the presence of a third body with a minimum mass of0.06M_⊙.For V0853 Aur,it is discovered that the O-C diagram of the system also shows a cyclic oscillation with a period of 9.64 yr and an amplitude of 0.03365 days.The cyclic oscillation of V0853 Aur can be attributed to the LTTE by means of a third body with a mass no less than 3.77M_⊙.The third body may play an important role in the formation and evolution of these systems.

Variable Stars in the 50BiN Open Cluster Survey.Ⅲ.NGC 884

Open clusters are the basic building blocks that serve as a laboratory for the study of young stellar populations in the Milky Way.Variable stars in open clusters provide a unique way to accurately probe the internal structure,temporal and dynamical evolutionary stages of individual stars and the host cluster.The most powerful tool for such studies is time-domain photometric observations.This paper follows the route of our previous work,concentrating on a photometric search for variable stars in NGC 884.The target cluster is the companion of NGC869,forming the well-known double cluster system that is gravitationally bound.From the observation run in 2016 November,a total of 9247 B-band CCD images and 8218Ⅴ-band CCD images were obtained.We detected a total of 15 stars with variability in visual brightness,including five Be stars,three eclipsing binaries,and seven of unknown types.Two new variable stars were discovered in this work.We also compared the variable star content of NGC 884 with its companion NGC 869.

Light curve solutions of six eclipsing binaries at the lower limit of periods for W UMa stars

Photometric observations are presented in V and I bands of six eclipsing binaries at the lower limit of the orbital periods for W UMa stars. Three of them are newly discovered eclipsing systems. The light curve solutions reveal that all shortperiod targets are contact or overcontact binaries and six new binaries are added to the family of short-period systems with estimated parameters. Four binaries have com- ponents that are equal in size and a mass ratio near 1. The phase variability shown by the V-I colors of all targets may be explained by lower temperatures on their back surfaces than those on their side surfaces. Five systems exhibit the O＇Connell effect that can be modeled by cool spots on the side surfaces of their primary components. The light curves of V1067 Her in 2011 and 2012 are fitted by diametrically opposite spots. Applying the criteria for subdivision of W UMa stars to our targets leads to ambiguous results.

Physical properties and catalog of EW-type eclipsing binaries observed byLAMOST

EW-type eclipsing binaries(hereafter called EWs)are strong interacting systems in which both component stars usually fill their critical Roche lobes and share a common envelope.Numerous EWs were discovered by several deep photometric surveys and there were about 40 785 EW-type binary systems listed in the international variable star index(VSX)by 2017 March 13.7938 of them were observed with LAMOST by 2016 November 30 and their spectral types were identified.Stellar atmospheric parameters of 5363 EW-type binary stars were determined based on good spectroscopic observations.In the paper,those EWs are cataloged and their properties are analyzed.The distributions of orbital period(P),effective temperature(T),gravitational acceleration(log(g)),metallicity([Fe/H])and radial velocity(RV)are presented for these observed EW-type systems.It is shown that about 80.6% of sample stars have metallicity below zero,indicating that EW-type systems are old stellar populations.This is in agreement with the conclusion that EW binaries are formed from moderately close binaries through angular momentum loss via magnetic braking that takes a few hundred million to a few billion years.The unusually high metallicities of a few percent of EWs may be caused by contamination of material from the evolution of unseen neutron stars or black holes in the systems.The correlations between orbital period and effective temperature,gravitational acceleration and metallicity are presented and their scatters are mainly caused by(i)the presence of third bodies and(ii)sometimes wrongly determined periods.It is shown that some EWs contain evolved component stars and the physical properties of EWs mainly depend on their orbital periods.It is found that extremely short-period EWs may be older than their long-period cousins because they have lower metallicities.This reveals that they have a longer timescale of pre-contact evolution and their formation and evolution are mainly driven by angular momentum loss via magnetic braking.

Spin Evolution of Neutron Stars in OB/X-ray Binaries

We have investigated the relation between the orbital period Porb and the spin period Ps of neutron stars in OB/X-ray binaries. By simulating the time-development of the mass loss rate and radius expansion of a 20M☉ donor star, we have calculated the detailed spin evolution of the neutron star before steady wind accretion occurs (that is, when the break spin period is reached), or when the OB star begins evolving off the main sequence or has filled its Roche lobe. Our results are compatible with the observations of OB/X-ray binaries. We find that in relatively narrow systems with orbital periods less than tens of days, neutron stars with initial magnetic field B0 stronger than about 3×1012 G can reach the break spin period to allow steady wind accretion in the main sequence time, whereas neutron stars with B0 < 3×1012 G and/or in wide systems would still be in one of the pulsar, rapid rotator or propeller phases when the companion evolves off the main sequence or fills its Roche lobe. Our results may help understand the various characteristics of the observed OB/neutron star binaries along with their distributions in the Ps-Porb diagram.

Photometric study of eclipsing binaries in the Large Magellanic Cloud--I.W UMa type binaries in the Large Magellanic Cloud

Eclipsing binaries are among the most important sources of information on stellar parameters like radii,masses,luminosities,etc.We present the analysis of six W UMa systems discovered in the Large Magellanic Cloud using the Wilson-Devinney method.

Physical Properties of 29 sdB+dM Eclipsing Binaries in Zwicky Transient Facility

The development of large-scale time-domain surveys provides an opportunity to study the physical properties as well as the evolutionary scenario of B-type subdwarfs(sdBs)and M-type dwarfs(dMs).Here,we obtained 33 sdB+dM eclipsing binaries based on the Zwicky Transient Facility(ZTF)light curves and Gaia Early Data Release3(EDR3)parallaxes.By using the PHOEBE code for light curve analysis,we obtain probability distributions for parameters of 29 sdB+dMs.R1,R2 and i are well determined,and the average uncertainty of mass ratio q is 0.08.Our parameters are in good agreement with previous works if a typical mass of sdB is assumed.Based on parameters of 29 sdB+dMs,we find that both the mass ratio q and the companion’s radius R2 decrease with the shortening of the orbital period.For the three sdB+dMs with orbital periods less than 0.075 days,their companions are all brown dwarfs.The masses and radii of the companions satisfy the mass–radius relation for low-mass stars and brown dwarfs.Companions with radii between 0.12 R_(⊙)and 0.15 R_(⊙)seem to be missing in the observations.As more short-period sdB+dM eclipsing binaries are discovered and classified in the future with ZTF and Gaia,we will have more information to constrain the evolutionary ending of sdB+dMs.

Light Curve Analysis and Period Study of Two Eclipsing Binaries UZ Lyr and BR Cyg

Two eclipsing binary systems,UZ Lyr and BR Cyg,are semi-detached types whose secondary component fills its Roche lobe.Although radial velocity and light curves of these systems have already been investigated separately,both their radial velocity and light curves are analyzed simultaneously for the first time in the present study.Also,the orbital period changes of these systems are studied.Our results show that the mass transfers between components have negligible effects on the orbital period changes of these systems,but two light travel time effects are the reasons for the periodic behavior of the O-C curve for UZ Lyr.We could not remark more information about orbital period changes for BR Cyg,but we find a new orbital period for it.By radial velocity and light curve analysis,we find a cold spot on the secondary component of BR Cyg.The new geometrical and physical parameters of both systems are obtained and their positions on the H-R diagram are demonstrated.

The First Photometric Analysis of Two Low Mass Ratio Totally Eclipsing Contact Binaries:TIC 393943031 and TIC 89428764

Photometric analysis of the contact binaries TIC 393943031 and TIC 89428764 was carried out using Transiting Exoplanet Survey Satellite and SuperWASP data for the first time.Using the Wilson–Devinney code,we have found that TIC 393943031 is a low-mass-ratio deep contact binary with a fillout factor of 50.9(±1)%and a mass ratio of q=0.163±0.001.TIC 89428764 is a medium and low-mass-ratio contact binary with a fillout factor of 34.5(±1)%and a mass ratio of q=0.147±0.001.Furthermore,the period study reveals both the stars exhibit continuously increasing periods,the increasing rate is 4.21×10^(−7)day yr^(−1) for TIC 393943031 while 6.36×10^(−7)day yr^(−1) for TIC 89428764.The possible reason is mass transfer from the secondary component to the primary component for both stars.Meanwhile,we discussed their evolutionary phases and orbital angular momenta.

New Apsidal Motion in Four Eccentric Eclipsing Binaries:V610 Car,V944 Cep,V2815 Ori and V1260 Tau

This paper presents an apsidal motion analysis.The apsidal motion analysis of the eccentric eclipsing binaries V610 Car(P=4.84 days),V944 Cep(P=6.56 days),V2815 Ori(P=2.13 days),and V1260 Tau(P=5.43 days)was performed using minima times from the O-C Gateway database,ASAS-3,ASAS-SN,and TESS,following Lacy’s approach.The rates of change of periastron longitude were found to be 0.0253±0.0041,0.0347±0.0015,0.0288±0.0010 and0.0294±0°.0079 cycle^(-1),respectively.From the light curve study,the first photometric mass ratio of V944 Cep was found to be q=1.4994±0.0012.A new light curve of V944 Cep was obtained using TESS data.The first absolute dimensions of V944 Cep were M_(1)=1.10±0.01 M_(⊙),M_(2)=1.64±0.02 M_(⊙),R_(1)=2.04±0.37 R_(⊙),R_(2)=3.77±0.67 R_(⊙)for the hotter primary component(T_(1)=4925 K),and M_(1)=1.04±0.01 M_(⊙),M_(2)=1.57±0.02 M_(⊙),R_(1)=2.26±0.36 R_(⊙),R_(2)=3.74±0.59 R_(⊙)for the cooler primary component(T_(1)=4475 K).For V610 Car,V944 Cep,V2815 Ori and V1260 Tau,the apsidal motion periods were found to be 188±26 yr,186±8 yr,73±3 yr and 182±38 yr,respectively.For V944 Cep,the internal structural constants of the component stars log_(k2,obs)=-2.05±0.01 and log_(k2,theo)=-1.83 for hotter primary component and log_(k2,obs)=-1.97±0.01 and log_(k2,theo)=-1.89 for cooler primary component were calculated.

Photometric investigations on two totally eclipsing contact binaries:V342 UMa and V509 Cam

By analyzing two sets of complete BV Rc Ic light curves for V342 UMa and three sets of complete BV Rc Ic light curves for V509 Cam, we determined that the two systems are both W-subtype contact binaries and that V342 UMa manifests a shallow contact configuration, while V509 Cam exhibits a medium contact configuration. Given that both of them are totally eclipsing binaries, the physical parameters derived only by the photometric light curves are reliable. Meanwhile, the period changes of the two targets were analyzed based on all available eclipsing times. We discovered that V342 UMa shows long-term period decrease with a rate of-1.02(±0.54)× 10^-7 d yr^-1 and that V509 Cam displays long-term period increase with a rate of 3.96(±0.90)× 10^-8 d yr^-1. Both the conservative mass transfer and angular momentum loss via magnetic stellar winds can be used to interpret the long-term period decrease of V342 UMa. The longterm period increase of V509 Cam can be explained by mass transfer from the less massive star to the more massive one. The absolute parameters of the two binaries were estimated according to their Gaia distances and our derived photometric solution results. This method can be extended to other contact binaries without radial velocities but with reliable photometric solutions. Their evolutionary states were investigated and we found that they reveal properties that are identical to other W-subtype contact systems.

Period variations of Algol-type eclipsing binaries AD And, TW Cas and IV Cas

We present new analyses of variations in O-C diagrams of three Algol-type eclipsing binary stars：AD And,TW Cas and IV Cas.We have used all published minima times（including visual and photographic）as well as newly determined ones from our and Super Wasp observations.We determined orbital parameters of 3^（rd） bodies in the systems with statistically significant errors,using our code based on genetic algorithms and Markov chain Monte Carlo simulations.We confirmed the multiple nature of AD And and the triple-star model of TW Cas,and we proposed a quadruple-star model of IV Cas.

Double-lined M dwarf eclipsing binaries from Catalina Sky Survey and LAMOST

Eclipsing binaries provide a unique opportunity to determine fundamental stellar properties. In the era of wide-field cameras and all-sky imaging surveys, thousands of eclipsing binaries have been reported through light curve classification, yet their basic properties remain unexplored due to the ex- tensive efforts needed to follow them up spectroscopically. In this paper we investigate three M2-M3 type double-lined eclipsing binaries discovered by cross-matching eclipsing binaries from the Catalina Sky Survey with spectroscopically classified M dwarfs from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope survey data release one and two. Because these three M dwarf binaries are faint, we further acquire radial velocity measurements using GMOS on the Gemini North telescope with R ~4000, enabling us to determine the mass and radius of individual stellar components. By jointly fitting the light and radial velocity curves of these systems, we derive the mass and radius of the primary and secondary components of these three systems, in the range between 0.28-0.42 MQ and 0.29-0.67 R, respectively. Future observations with a high resolution spectrograph will help us pin down the uncertainties in their stellar parameters, and render these systems benchmarks to study M dwarfs, providing inputs to improving stellar models in the low mass regime, or establishing an empirical mass-radius relation for M dwarf stars.

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

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.

Photometric investigation of eight ultra-short period eclipsing binaries from OGLE

We performed a detailed photometric analysis of eight ultra-short period eclipsing binaries(USPEBs) using the Wilson-Devinney method. We present the modeled light curves and derived photometric solutions. The USPEBs with period(P)≤0.21 d considered in our study belong to W-subtype having shallow contact factor(f)<~20%, high mass ratio(q)>~0.7 and later spectral types. The absolute parameters for these short-period binaries were derived applying empirical relations. We discuss the evolutionary stage of these USPEBs using the mass-radius, color-density and period-color diagrams. The objects showed poor metallicities, and some objects were even found to be existing around fully convective limits. The period distribution of USPEBs exhibited a sharp cut-off at 0.22 d;however, we observed significant deficits for our objects in the literature. We examined the statistics of USPEBs studied to date(in terms of the distribution of period, mass ratio and component temperatures of USPEBs) and observed that a dominant distribution of component temperatures for these USPEBs was towards lower temperatures.

Absolute parameters of the three totally-eclipsing W UMa stars NSVS 2443858,NSVS 780649 and V1098 Her

We present the first photometric analysis of three totally-eclipsing W UMa binaries,NS VS2443858,NSVS 780649 and V1098 Her.The absolute astrophysical parameters of the stellar components were determined by means of Gaia distances and light curve solutions.The results show that:(ⅰ)Two of the systems,NSVS 2443858 and V1098 Her,are of A subtype while the obtained temperature of the secondary component of NSVS 780649 indicates that it is a W-subtype system;(ⅱ)The estimated mass ratios approach the lower limit of the mass ratio assumed by researchers in recent years so our targets could be classified as extreme mass ratio binary(EMRB)systems;(ⅲ)All the systems have deep contact configurations,so they also are deep low mass ratio(DLMR)systems;(ⅳ)The components of our systems are stars of F and G spectral type and undergo total eclipses;(ⅴ)The sum 0.871 M⊙of the component masses of NSVS 780649 is below the mass limit of 1.0-1.2 M⊙assumed for the known contact binary stars.

A photometric study of two neglected eclipsing binaries

We present the first BVR photometry,period variation and photometric light curve analysis of two poorly studied eclipsing binaries,V1321 Cyg and CR Tau.Observations were carried out from November 2017 to January 2020 at the observatory of Uzhhorod National University.Period variations were studied using all available early published as well as our minima times.We used the newly developed ELIS a code for the light curve analysis and determination of photometric parameters for both systems.We found that V1321 Cyg is a close detached eclipsing system with a low photometric mass ratio of q=0.28 which suggests that the binary is a post-mass transfer system.No significant period changes in this system are detected.CR Tau is,on the other hand,a semi-detached system where the secondary component almost fills its Roche lobe.We detected a long-term period increase at a rate of 1.49 × 10^(-7) d yr^(-1),which supports mass transfer from the lower mass secondary component to the more massive primary.

Absolute physical parameters of three poorly studied detached eclipsing binaries

The photometric and spectroscopic data for three double-lined detached eclipsing binaries were collected from the photometric and spectral surveys.The light and radial velocity curves of each binary system were simultaneously analyzed using Wilson-Devinney(WD)code,and the absolute physical and orbital parameters of these binaries were derived.The masses of both components of ASASSN-V J063123.82+192341.9 were found to be M1=1.088±0.016 and M20.883±0.016 M⊙;those of ASAS J011416+0426.4 were determined to be M1=0.934±0.046 and M2=0.754±0.043 M⊙;and those of MW Aur were derived to be M1=2.052±0.196 and M21.939±0.193 M⊙.Finally,the evolutionary status of these detached binaries was discussed based on their absolute parameters and the theoretical stellar models.

Long-period eclipsing binaries:towards the true mass-luminosity relation.I.the test sample,observations and data analysis

The mass-luminosity relation is a fundamental law of astrophysics.We have suggested that the currently used mass-luminosity relation is not correct for the M/M⊙>2.7 range of mass since it was created utilizing double-lined eclipsing binaries,where the components are synchronized and consequently change each other's evolutionary path.To exclude this effect,we have started a project to study longperiod massive eclipsing binaries in order to construct radial velocity curves and determine masses for the components.We outline our project and present the selected test sample together with the first HRS/SALT spectral observations and the software package,FITTING BINARY STARS(FBS),that we developed for the analysis of our spectral data.As the first result,we present the radial velocity curves and best-fit orbital elements for the two components of the FP Car binary system from our test sample.

Discovery of four W UMa type eclipsing binaries in the field of open cluster ASCC 5

We carried out time-series photometric observations in the Re-band of the young, poorly studied open cluster ASCC 5 during November and December, 2012, to search for magnetically active stars, and discovered four eclipsing binary stars in this field. In order to characterize these four newly discovered binaries, we derived their orbital periods by their times of light minimum, estimated their effective tem- peratures based on their （J - H） colors and analyzed their light curves using the Wilson-Devinney light curve modeling technique. Our analyses reveal that all of them are contact binaries with short orbital periods of less than 0.5 d, with spectral types from late-F to mid-K. Among them, one is a typical A subtype contact binary with a mass ratio around 0.5 and a period of 0.44 d, and one is an H subtype contact binary with a high mass ratio around 0.9 and a short period of about 0.27 d. The other two systems show low amplitudes of light variation （Ant 〈0.11m）; their actual photomet- ric mass ratios could not be determined by the light curve modelings, probably due to their attributes of being partially eclipsing stars. A preliminary analysis for these two systems indicates that both of them are likely to be W subtype contact binaries with low orbital inclinations. In addition, both of these two low amplitude variables show asymmetric distorted light curves （e.g., O＇Connell effect of ARc --~0.02m） during the observing runs, suggesting the presence of starspots on these two systems. More inter- estingly, the one showing a large case of the O＇Connell effect presented a remarkable variation in the shape of the light curve on a time scale of one day, indicating that this star is in a very active state. Therefore, these two stars need spectroscopic observations to precisely determine their parameters, as well as further photometric observations to understand the properties of their magnetic activity, e.g., the evolution of starspots.