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.     

ASAS J174406+2446.8 is identified as a marginal-contact binary with a possible cool third body

ASAS J174406+2446.8 was originally found as a δ Scuti-type pulsating star with the period P=0.189068 d by ASAS survey.However,the LAMOST stellar parameters reveal that it is far beyond the red edge of pulsational instability strip on the log g-T diagram of δ Scuti pulsating stars.To understand the physical properties of the variable star,we observed it by the 1.0-m Cassegrain reflecting telescope at Yunnan Observatories.Multi-color light curves in B,V,R_c and I_c bands were obtained and are analyzed by using the W-D program.It is found that this variable star is a shallow-contact binary with an EB-type light curve and an orbital period of 0.3781 d rather than a δ Scuti star.It is a W-subtype contact binary with a mass ratio of 1.135(±0.019) and a fill-out factor of 10.4%(±5.6)%.The situation of ASAS J174406+2446.8 resembles those of other EB-type marginal-contact binaries such as UU Lyn,Ⅱ Per and GW Tau.All of them are at a key evolutionary phase from a semi-detached configuration to a contact system predicted by the thermal relaxation oscillation theory.The linear ephemeris was corrected by using 303 new determined times of light minimum.It is detected that the O-C curve shows a sinusoidal variation that could be explained by the light-travel-time effect via the presence of a cool red dwarf.The present investigation reveals that some of the δ Scuti-type stars beyond the red edge of pulsating instability strip on the log g-T diagram are misclassified eclipsing binaries.To understand their structures and evolutionary states,more studies are required in the future.     

Modern comprehensive study of the W UMa system TY Boo

New three color light curves of TY Boo were acquired during five nights from February to May 2006 in the BV R bandpass using a 50-cm F/8.4 RitcheyChr′etien telescope(Ba50)at the Baja Astronomical Observatory(Hungary),with a512×512 Apogee AP-7 CCD camera.A photometric solution of these light curves was obtained by means of the Wilson-Devinney code.The results showed that the less massive component is hotter than the more massive one,and the temperature difference between the components is △T～249 K.Long term investigation of the system based on all available data shows two stages of increase and a similar trend for decrease,which appears to be periodic behavior.A set of new light elements yields a new period(P=0.3171506d)and shows a periodic decrease with the rate d P/d E=5.858×10-12d cycle-1,6.742×10-9d yr-1or 0.058 s century-1.The evolutionary status of the system is discussed.     

Pulsation analysis of the high amplitude δ Scuti star CW Serpentis

Time-series photometric observations were made for the high amplitudeδScuti star CW Ser between 2011 and 2012 at the Xinglong Station of National Astronomical Observatories,Chinese Academy of Sciences.After performing the frequency analysis of the light curves,we confirmed the fundamental frequency of f=5.28677 c d 1,together with seven harmonics of the fundamental frequency,which are newly detected.No additional frequencies were detected.The O C diagram,produced with the 21 newly determined times of maximum light combined with those provided in the literature,helps to obtain a new ephemeris formula of the times of maximum light with the pulsation period of 0.189150355±0.000000003 d.     

New CCD photometric investigation of high amplitude δ Scuti star V2455 Cyg

New V-band CCD observations of variable star V2455 Cyg were performed during two nights in September 2017. According to all times of maximum light and new maxima, the O-C curve was analyzed.The period changes of V2455 Cyg were investigated and the rate of increasing period was obtained to be(1/P) d P/dt = 1.99 × 10~(-7) yr~(-1). Frequency analysis indicated that V2455 Cyg pulsates with the radial p mode and the fundamental frequency is 10.61574 d-1. Physical parameters of V2455 Cyg at mean temperature were determined(e.g., R = 2.52 R_⊙and M = 1.92 M_⊙). The position of this star in the H-R diagram confirms that V2455 Cyg is a high amplitude δ Scuti star.     

Multi-color light curves and orbital period research of eclipsing binary V1073 Cyg

New multi-color BV RcIcphotometric observations are presented for the W UMa type eclipsing binary V1073 Cyg. The multi-color light curve analysis with the Wilson-Devinney procedure yielded the absolute parameters of this system, showing that V1073 Cyg is a shallow contact binary system with a fill-out factor f = 0.124(±0.011). We collected all available times of light minima spanning 119 yr,including CCD data to construct the O-C curve, and performed detailed O-C analysis. The O-C diagram shows that the period change is complex. A long-term continuous decrease and a cyclic variation exist. The period is decreasing at a rate of P =-1.04(±0.18) × 10~(-10) d cycle~(-1) and, with the period decrease, V1073 Cyg will evolve to the deep contact stage. The cyclic variation with a period of P_3= 82.7(±3.6) yr and an amplitude of A = 0.028(±0.002) d may be explained by magnetic activity of one or both components or the light travel time effect caused by a distant third companion with M_3(i′= 90?) = 0.511 M_⊙.     

First photometric study of ultrashort-period contact binary 1SWASP J140533.33+114639.1

In this paper,CCD photometric light curves for the short-period eclipsing binary 1 SWASP J140533.33+114639.1(hereafter J1405) in the BV R bands are presented and analyzed using the 2013 version of the Wilson-Devinney(W-D) code. It is discovered that 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 asymmetric light curves of the system,a cool starspot on the more massive component is employed. This shallow contact eclipsing binary may have been formed from a short-period detached system through orbital shrinkage due to angular momentum loss. Based on the(O-C) method,the variation of orbital period is studied using all the available times of minimum light. The(O-C) diagram reveals that the period is increasing continuously at a rate of d P/dt = +2.09×10~(-7) d yr~(-1),which can be explained by mass transfer from the less massive component to the more massive one.     

OO Aquilae:a solar-type contact binary with intrinsic light curve changes

New multi-color photometry of the solar-type contact binary OO Aql was obtained in 2012 and2013, using the 60 cm telescope at Xinglong Station of the National Astronomical Observatories, Chinese Academy of Sciences. From two sets of light curves LC_1 and LC_2, photometric models were performed by using the 2003 version of the Wilson-Devinney code. The overcontact factor of the binary system was determined to be f = 37.0(±0.5)%. The intrinsic variability of this binary occurs in light maxima and minima, which could result from a possible third component and magnetic activity of the late type components. Based on all available light minimum times, the orbital period may change in a complicated mode,i.e., sudden period jumps or continuous period variations. The period of OO Aql may possibly undergo a secular period decrease with a rate of d P /dt =-3.63(±0.30) × 10~(-8)d yr~(-1), superimposed by two possible cyclic variations in the O- C curve. The long-term period decrease may be interpreted as conserved mass transfer from the more massive component to the less massive one. The 21.5-yr oscillation may be attributed to cyclic magnetic activity, and the 69.3-yr one may result from the light-time effect of an unseen tertiary body.     

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.     

1SWASP J034439.97+030425.5: a short-period eclipsing binary system with a close-in stellar companion

First multi-wavelength photometric light curves(LCs) of the short-period eclipsing binary(EB)1 SWASP J034439.97+030425.5(hereafter J0344) are presented and analyzed by using the 2013 version of the Wilson-Devinney(W-D) code. To explain the asymmetric LCs of J0344, a cool star-spot on the less massive component was employed. The photometric solutions suggest that J0344 is a W-subtype shallow contact EB with a contact degree of f = 4.9% ± 3.0% and a mass ratio of q = 2.456 ± 0.013. Moreover,an obvious third light was detected in our analysis. We calculated the average luminosity contribution of the third light to the total light, and that value reaches up to 49.78%. Based on the O-C method,the variations of the orbital period were studied for the first time. Our O-C diagram reveals a secular decrease superimposed on a cyclic oscillation. The orbital period decreases at a rate of d P/dt =-6.07 ×10~(-7) d yr~(-1), which can be explained by the mass transfer from the more massive component to the less massive one. Besides, its O-C diagram also shows a cyclic oscillation with an amplitude of 0.0030 d and a period about 7.08 yr, which can be explained by the presence of a third body with a minimum mass of M3 min= 0.15 ± 0.02 M_⊙. The third component may play an important role in the formation and evolution of J0344 by drawing angular momentum from the central system.     

LO And: an A-subtype contact binary with a very cool third component

Despite the intensive investigations since the discovery of LO And approximately 60 yr ago, its evolutionary status and subtype are still a matter of controversy. By simultaneously modeling the radialvelocity curves and new light curves with the Wilson-Devinney code, we present new geometric,photometric and absolute parameters for this system. The simultaneous solution suggests that LO And is an A-subtype contact binary with a contact degree of 32.4%. The absolute parameters are modified to become M_1= 1.409 M⊙, M_2= 0.449 M⊙, R_1= 1.36 R⊙and R_2= 0.83 R⊙. From our observations and data from surveys, we determined 334 eclipse timings. The O-C diagram, constructed from the new eclipse timings and those reported in the literature, reveals a secular increase and a cyclic variation in its orbital period. The former is caused by conservative mass transfer from the secondary component with less mass to the primary one with more mass. The latter may be explained by either the cyclic magnetic activity on the two components or the light-time effect due to a third body. With the absolute physical parameters,we investigated its evolutionary status, and find that LO And is an unevolved contact binary undergoing thermal relaxation oscillation, which will eventually coalesce into a single star with rapid rotation.     

Photometric study and period analysis of the W UM-type binary system QW Gem

New multi-color photometric observations of the previously unstudied contact binary QW Gem are presented. Completely covered BVRI band light curves were obtained, including four new times of light minima. The light curves were simultaneously analyzed with the 2013 version of the Wilson-Devinney method, assuming a third light. The photometric solutions confirm that QW Gem is a W-type W UMa system with a fill-out factor of f~17%. The absolute parameters of the components were determined to be M_p= 1.33 ± 0.03 M_☉,M_s = 0.44 ± 0.01 M_☉,R_p = 1.25 ± 0.01 R_☉,R_s = 0.77 ± 0.01 R_☉,Lp= 1.68 ± 0.03 L_☉ and L_s = 0.68 ± 0.01 L_☉. The orbital period change of QW Gem was investigated by the O-C method using all available data. The results show that this binary system could have undergone a continuous orbital period decrease during the past two decades at a rate of about dP/dt =-2.55 × 10~(-7) d yr~(-1). In addition, a small-amplitude oscillation was detected to be superimposed on a long-term decrease.     

Absolute parameters and observed flares in the M-type detached eclipsing binary 2MASS J04100497+2931023

The eclipsing binary 2 MASS J04100497+2931023(J04100497+2931023) is classified its spectral type of M0±2 V on basis of a low-resolution spectral survey by the Large Sky Area Multi-Object Fiber Spectroscopic Telescope(LAMOST). The low-resolution spectra exhibit strong single-peak emission in the Hα line. We obtained the radial velocities of this binary by means of the Cross-Correlation Function method from the LAMOST medium-resolution spectra. Both components of J04100497+2931023 indicate strong emissions in the Hα line. We performed follow-up photometric observations of J04100497+2931023 using the Xinglong 85 cm telescope of National Astronomical Observatories, Chinese Academy of Sciences. We obtained its full light curve in V RI filters. We first determined their absolute parameters from simultaneously radial velocity and light curves by the Wilson-Devinney program. From our new light curves, we detected three flares for the first time, including one convective flare. The amplitudes,durations, energies, and spectral indices of three flares were also determined. J04100497+2931023 was monitored for approximately 29 h, which indicates that the flare rate is 0.1 flare per hour. We conclude that J04100497+2931023 is a low-mass detached eclipsing binary with strong magnetic activity.     

New CCD photometric investigation of the early-type overcontact binary BH Cen in the young star-forming Galactic cluster IC 2944

BH Cen is a short-period early-type binary with a period of 0.792 din the extremely young star-forming cluster IC 2944. New multi-color CCD photometric light curves in U, B, V, R and I bands are presented and are analyzed by using the Wilson-Devinney code. It is detected that BH Cen is a high-mass-ratio overcontact binary with a fill-out factor of 46.4% and a mass ratio of 0.89. The derived orbital inclination i is 88.9 degrees, indicating that it is a totally eclipsing binary and the photometric parameters can be determined reliably. By adding new eclipse times, the orbital period changes in the binary are analyzed. It is confirmed that the period of BH Cen shows a long-term increase while it undergoes a cyclic oscillation with an amplitude of A_3 = 0.024 d and a period of P_3 = 50.3 yr. The high mass ratio, overcontact configuration and long-term continuous increase in the orbital period all suggest that BH Cen is in the evolutionary state after the shortest-period stage of Case A mass transfer.The continuous increase in period can be explained by mass transfer from the secondary component to the primary one at a rate of˙M_2 = 2.8×10~(-6) M_⊙per year. The cyclic change can be plausibly explained by the presence of a third body because both components in the BH Cen system are early-type stars. Its mass is determined to be no less than 2.2 M_⊙at an orbital separation of about 32.5 AU. Since no third light was found during the photometric solution, it is possible that the third body may be a candidate for a compact object.     

New photometric investigation of the low-mass-ratio contact binary star V1853 Orionis

Four-color charge-coupled device(CCD) light curves in the B, V, Rc and I c bands of the totaleclipsing binary system V1853 Orionis(V1853 Ori) are presented. By comparing our light curves with those published by previous investigators, it is determined that the O'Connell effect on the light curves has disappeared. By analyzing those multi-color light curves with the Wilson-Devinney code(W-D code),it is discovered that V1853 Ori is an A-type intermediate-contact binary with a degree of contact factor of f = 33.3%(3.7%) and a mass ratio of q = 0.1896(0.0013). Combining our 10 newly determined times of light minima together with others published in the literature, the period changes of the system are investigated. We found that the general trend of the observed minus calculated(O-C) curve shows a downward parabolic variation that corresponds to a long-term decrease in the orbital period with a rate of d P/dt =-1.96(0.46)×10^-7 d yr^-1. The long-term period decrease could be explained by mass transfer from the more-massive component to the less-massive one. By combining our photometric solutions with data from Gaia DR_2, absolute parameters were derived as M_1 = 1.20 M⊙, M_2 = 0.23 M⊙, R_1 = 1.36 R⊙and R_2 = 0.66 R⊙. The long-term period decrease and intermediate-contact configuration suggest that V1853 Ori will evolve into a high fill-out overcontact binary.     

Photometric investigation of the K-type extremely shallow contact binary V1799 Orion

New multi-color light curves of the very short period K-type eclipsing binary V1799 Ori were obtained and analyzed with the Wilson-Devinney code. The photometric solutions reveal that the system is a W-type shallow-contact binary with a mass ratio of q = 1.335(±0.005) and a degree of contact of about f = 3.5(±1.1)%.In general, the results are in good agreement with what is reported by Samec. Dramatic manifestations of the O'Connell effect that appear in the light curves can be explained well by employing starspots on the binary surface, which confirms that the system is active at present. Several new times of light minimum were obtained. All the available times of light minimum were collected, along with the recalculated and newly obtained values. Applying a least-squares method to the constructed O- C diagram,a new ephemeris is derived for V1799 Ori. The orbital period is found to show a continuous weak increase at a rate of 1.8(±0.6) × 10-8d yr-1. The extremely shallow contact, together with the period increase, suggests that the binary may be at a critical stage predicted by thermal relaxation oscillation theory.     

Three-dimensional orbit and physical parameters of HD 6840

HD 6840 is a double-lined visual binary with an orbital period of ～7.5 years. By fitting the speckle interferometric measurements made by the 6 m BTA telescope and 3.5 m WIYN telescope, Balega et al. gave a preliminary astrometric orbital solution of the system in 2006. Recently, Griffin derived a precise spectroscopic orbital solution from radial velocities observed with OPH and Cambridge Coravel.However, due to the low precision of the determined orbital inclination, the derived component masses are not satisfying. By adding the newly collected astrometric data in the Fourth Catalog of Interferometric Measurements of Binary Stars, we give a three-dimensional orbit solution with high precision and derive the preliminary physical parameters of HD 6840 via a simultaneous fit including both astrometric and radial velocity measurements.     

RT Leonis Minoris： an Unstable W Ursae Majoris System with a Spotted Component

Complete BV light curves of the W UMa type binary RT LMi are presented. From the observations, four times of minimum light were determined. Based on the new times of minimum light and those collected from the literature, changes in the orbital period of the system were found and analyzed with Kalimeris et al.'s method. The result shows that the orbital period possibly oscillates with a cycle of about 64 years and an amplitude of 1.2 × 10-6 days. The present CCD photometric observations reveal that the light curves are obviously asymmetrical, and show a positive O'Connell effect, while the light curves obtained in 1982 exhibit a negative O'Connell effect. The present light curves were analyzed by means of the latest version of the Wilson-Devinney code, which was also used to correct the photometric effects, including the distortion on the radial-velocity curves obtained by Rucinski et al. The following absolute dimensions have been derived: MI -1.28 ±0.08 M⊙, M2 = 0.48 ±0.06 M⊙, R1 = 1.28 ±0.06 R⊙,     

Period investigation of Algol systems TZ Eri and TU Her

TZ Eri and TU Her are both classic Algol-type systems(Algols). By observing and collecting times of minimum light, we constructed the O-C curves for the two systems. The long-time upward and downward parabolas shown in these diagrams are considered to be the result of the combination of mass transfer and angular momentum loss. The secular orbital period change rates are d P/dt = 4.74(±0.12) ×10~(-7) d yr~(-1) and d P/dt =-2.33(±0.01) × 10~(-6) d yr~(-1), respectively. There are also cyclic variations in their O-C curves which might be caused by the light-travel time effect(LTTE). A circumbinary star may exist in the TZ Eri system with a mass of at least 1.34 M_⊙, while there are possibly two celestial bodies that almost follow a 2 : 1 resonance orbit around the TU Her binary pair. Their masses are at least 2.43 M_⊙and 1.27 M_⊙.     

V2551 Cyg:a pulsating star with enigmatic peculiarities

Intensive photometric and spectral observations of the variable star V2551 Cyg are presented.The light curve shape reveals that the target is a pulsating star, contrary to its previous classification as an eclipsing binary. The period and amplitude of the light curve, the amplitudes of color changes and the radial velocity curve of V2551 Cyg are similar to those of a high-amplitude δ Scuti variable. The target seems to pulsate with the fundamental mode. However, V2551 Cyg exhibits several important peculiarities:(i) the decreasing branch of its light curve is steeper than the increasing one;(ii) the radial velocity curve has a flat section in the phase range 0.7–1.2 and short increase of the negative radial velocity at phase 0.7;(iii) the rotational velocity is quite big for a HADS star;(iv) the Fourier coefficients of V2551 Cyg are quite different from those of HADS stars. The target classification is difficult due to these peculiarities.