KIC 5197256: an eclipsing binary containing a δ Scuti variable star

This paper reports analysis of an eclipsing binary system KIC 5197256 with a δ Sct variable component.Utilizing light-curve modeling,several stellar parameters are derived,e.g.,temperature,mass,and mass ratio.The O-C diagram is a straight line with a negative slope which means that its period is almost constant for about 2 yr.Frequency analyses are performed for the residual light curve after subtracting the binary variations.The frequency spectrum reveals that one component star is a δ Scuti variable.Large frequency separation is cross-identified with the histogram graph and the Fourier transform method.Based on the large separation and density relationship,the mean density of the δ Sct component is estimated to be 0.05 g·cm~(-3).Five frequencies with the same frequency spacing in the range of 25 d~(-1)-34 d~(-1) are detected.Statistically,the pulsation amplitudes of δ Sct stars increase with decreasing of rotations,so we propose that KIC 5197256 might have a relatively large rotational velocity,and the frequency f_(10) might be the rotation frequency.     

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.     

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.     

A study of variable stars in the open cluster NGC 1582 and its surrounding field

This paper presents Charge-Coupled Device time-series photometric observations of the open cluster NGC 1582 and its surrounding field with Johnson B,V and R filters by using the Nanshan 1 m telescope administered by Xinjiang Astronomical Observatory.19 variable stars and three variable candidates were detected in a 45′×48.75′ field around the cluster.12 of the variable stars are newly-discovered variable objects.The physical properties,classifications and memberships of these 22 objects are studied through their light curves,their positions on the color-magnitude diagram and with archival data from the Naval Observatory Merged Astrometric Dataset.Among these objects,five are eclipsing binary systems,six are pulsating variable stars including one known S Scuti star and one newly-discovered RR Lyrae star.The distance to the RR Lyrae star is estimated to be 7.9 ± 0.3 kpc,indicating that the star is located far behind the cluster.Four variable stars are probable members of the cluster,and 13 of the 22 objects are confirmed to be field stars.     

A low-mass-ratio and deep contact binary as the progenitor of the merger V1309 Sco

Nova Sco 2008(=V1309 Sco) is an example of a V838 Mon type eruption rather than a typical classical nova. This enigmatic object was recently shown to have resulted from the merger of two stars in a contact binary. It is the first stellar merger that was identified to be undergoing a common envelope transient. To understand the properties of its binary progenitor, the pre-outburst light curves were analyzed by using the W-D method. The photometric solution of the 2002 light curve shows that it is a deep contact binary(f = 89.5(±40.5)%) with a mass ratio of 0.094. The asymmetry of the light curve is explained by the presence of a dark spot on the more massive component. The extremely high fill-out factor suggests that the merging of the contact binary is driven by dynamical mass loss from the outer Lagrange point. However,the analysis of the 2004 light curve indicates that no solutions were obtained even at an extremely low mass ratio of q = 0.03. This suggests that the common convective envelope of the binary system disappeared and the secondary component spiraled into the envelope of the primary in 2004. Finally, the ejection of the envelope of the primary produced the outburst.     

The high-amplitude δ Scuti variable CY Aqr is probably a triple system

Data representing 864 times of light maxima of the high-amplitude δ Scuti star CY Aqr were collected from the literature,based on which,long-term period changes of the variable star were investigated.A revised period and new ephemerides were given for the pulsating star.Remarkable cyclic variations were found in the O-C residuals which can be attributed to the light-time effects due to probable unseen components of the object.By using Kopal's method,the orbital parameters of the supposed component stars were derived.The solution suggests that CY Aqr is very probably in a triple system orbited eccentrically by two low-mass companions with periods of 54.2 and 47.3 yr.The lower limits on masses were estimated as0.04 M_⊙and 0.02 M_⊙,respectively,for the two hidden companions.     

Period–Luminosity Relationship for δ Scuti Stars Revisited

The Gaia DR3 parallax approach was used to estimate the absolute parameters of 2375 δ Scuti stars from the ASAS catalog.The selected stars have a variety of observational characteristics,with a higher than 80% probability of being δ Scuti stars.We have displayed all the stars in the Hertzsprung-Russell diagram along with the δ Scuti instability strip,the Zero Age Main Sequence and the Terminal Age Main Sequence.Then,we determined which fundamental and overtone modes each star belongs to using pu...     

Physical properties of γ Doradus pulsating stars and their relationship with long-period δ Scuti variables

We present LAMOST data on 168 γ Doradus(γ Dor) pulsating stars including stellar atmospheric parameters of 137 variables and spectral types for all of the samples. The distributions of period(P), temperature(T), gravitational acceleration(log(g)) and metallicity [Fe/H] are shown. It is found that most γ Dor variables are main-sequence stars with early F spectral types and temperatures from 6880 K to7280 K. They are slightly more metal poor than the Sun with a metallicity range from-0.4 to 0. On the H-R and log g-T diagrams, both the γ Dor and δ Scuti(δ Sct) stars occupy in the same region and some are beyond the borders predicted by current stellar pulsation theories. It is discovered that the physical properties of γ Dor stars are similar to those of long-period δ Sct(P 0.3 d) stars. The stellar atmospheric parameters are all correlated with the pulsation period for short-period δ Sct variables(P 0.3 d), but there are no such relations for γ Dor or long-period δ Sct stars. These results reveal that γ Dor and long-period δ Sct are the same group of pulsating stars and they are different from short-period δ Sct variables. Meanwhile, 33γ Dor stars are identified as candidates of binary or multiple systems.     

On the Rd Edge of the δ Scuti Instability Strip

The δ Scuti star ctalogue is used to derive the observational locations of such stars on the HR diagram.The theoretical and observational instability strips are compared to check the theoretical red edge obtained by considering nonlocal time-dependent convection theory.The observational instability strip almost overlaps with the theoretical one,but the observed blue and red envelopes are hotter overlaps with the theoretical one,but the observed blue and red envelopes are hotter than the theoretical edges.The distribution of δ Scuti stars in the pulsation strip is not uniform.     

Spectroscopic and photometric studies of a candidate pulsating star in an eclipsing binary:V948 Her

Eclipsing binary stars with a pulsating component are powerful tools that allow us to probe the stellar interior structure and the evolutionary statuses with a good accuracy. Therefore, in this study,spectroscopic and photometric examinations of an eclipsing binary system V948 Her are presented. The primary component of the system is classified to be a candidate δ Scuti variable in the literature. The fundamental stellar, atmospheric and orbital parameters, and the surface abundance of the star were determined and the pulsation behaviour was investigated in this study. The orbital parameters were derived by the analysis of radial velocity and Super WASP light curves. The spectral classification was found to be F2V. The initial atmospheric parameters of the primary component were derived by analysis of the spectral energy distribution and hydrogen lines. The final atmospheric parameters and chemical abundances of the primary component were obtained by using the method of spectrum synthesis. As a result, the final atmospheric parameters were determined as T_(eff)= 7100±200 K, log g= 4.3±0.1 cgs and ξ = 2.2 ± 0.2 km s~(-1). The surface abundance was found to be similar to solar. The fundamental stellar parameters of both components were also obtained to be M = 1.722 ± 0.123, 0.762 ± 0.020 M⊙, R =1.655 ± 0.034, 0.689 ± 0.016 R⊙for primary and secondary components, respectively. The pulsation characteristic of the primary component was examined using Super WASP data and the pulsation period was found to be ~0.038 d. The position of the primary pulsating component was also obtained inside the instability strip of δ Sct stars. The primary component of V948 Her was defined to be a δ Sct variable.     

Eclipsing binary XZ CMi in a hierarchical quadruple system

The new complete BV Rc Ic light curves and spectra of the short-period eclipsing binary XZ CMi are presented. The results from the combined analysis based on the photometric and spectroscopic data show that XZ CMi is a near contact binary with the secondary component filling its critical Roche lobe while the primary filling 91% of its Roche lobe. The investigation of the O-C diagram reveals that its orbital period is continuously increasing, which is consistent with the derived configuration and caused by the mass transfer from the less massive star to the more massive one. In addition, an obvious periodic modulation with the amplitude of0.0187(±0.0016) d and a high eccentric of 0.86(±0.04) is detected, which could be the results of the light time effect as a third star with the mass no less than 0.42(±0.09) M⊙orbiting around the central eclipsing binary once every 95.7(±2.1) yr. Furthermore, we found a visual companion star at 2.4′′ east by south of this system at a much greater distance by direct image. The large third light contribution found from the light curve analysis could be well explained by the existence of the third star and the fourth visual one.The similar parallax and proper motion imply that the components of this hierarchical quadruple system might be bounded by gravitation. Spectroscopic observations for two visual components were carried out by the LAMOST and 2.16 m telescopes, respectively. Their different values of [Fe/H] suggest that they were not born from the same origin. Thus, XZ CMi system is an interesting and important target to study the formation of the multiple stars.     

Investigating variable stars in the open cluster NGC 1912 and its surrounding field

In this work,we studied the variable stars in the open cluster NGC 1912 based on the photometric observations and Gaia DR2 data.More than 3600 CCD frames in B,V,R filters were reduced,and we obtained the light curves that span about 63 hours.By analyzing these light curves,we detected 24 variable stars,including 16 periodic variable stars,seven eclipsing binaries and one star whose type is unclear.Among these 24 variable stars,11 are newly discovered,which are classified as sixγDoradus stars,oneδScuti star,three detached binaries and one contact binary.We also confirmed 13 previously known variable stars.Based on cluster members identified by Cantat-Gaudin et al.(2018),we inferred cluster memberships for these detected variable stars.Using Gaia DR2 data,we plotted a new color-magnitude diagram for NGC1912,and showed the nature of variable cluster members in kinematical properties and heliocentric distance.Among the 24 variable stars,seven variables are probable cluster members,which show homogeneity in kinematic characters and space position with the established cluster members.Four of the seven variable cluster members are the previously discovered stars,consisting of twoγDor stars and twoδSct stars.The remaining three variable cluster members,which are allγDor stars,are firstly detected in this work.The main physical parameters of these variable cluster members estimated from the color-magnitude diagram are log(age/yr)=8.75,[Fe/H]=-0.1,m-M=10.03 mag,and E(B-V)=0.307.     

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.     

High amplitude δ Scuti star BO Lyn with evidence of a late A-type companion in an elliptical orbit

We present 145 times of light maximum for high amplitude δ Scuti star BO Lyn based on several sky surveys(CRTS,DASCH,NSVS,OMC and Super WASP)and our photometric observations.Combining with the data in literature,a total of 179 times of light maximum are used to analyze the O-C diagram of BO Lyn.We find that it can be described by an upward parabolic component and a periodic variation with a period of 34.5±0.1 yr.The latter could be caused by the light travel time effect as a result of an additional companion orbiting in a highly elliptical orbit(e=0.64±0.03).Our study indicates that the companion’s luminosity cannot be ignored,and it should be a late A-type main-sequence star.The long-term period change of BO Lyn is also detected,and its value,1.52±0.26×10~(-3)d Myr~(-1),is consistent with evolutionary models.We suggest that more spectroscopic and photometric observations are needed in the future to confirm the nature of the BO Lyn system.     

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.     

The first photometric analysis of the totally eclipsing contact binary V811 Cep

The first photometric analysis of V811 Cep was carried out.The first complete light curves of V,R and I bands are given.The analysis was carried out by the Wilson-Devinney(W-D) program,and the results show that V811 Cep is a median-contact binary(f=33.9(±4.9) %) with a mass ratio of 0.285.It is a W-subtype contact binary,that is,the component with less mass is hotter than the component with more mass,and the light curves are asymmetric(O' Connell effect),which can be explained by the existence of a hot spot on the component with less mass.The orbital inclination is i=88.3°,indicating that it is a totally eclipsing binary,so the parameters obtained are reliable.Through the O-C analyzing,it is found that the orbital period decreases at the rate of ■=-3.90(±0.06) × 10~(-7)d yr~(-1),which indicates that the mass transfer occurs from the more massive component to the less massive one.     

New variable stars from the photographic archive: semi-automated discoveries,attempts at automatic classification and the new field 104 Her

Using 172 plates taken with the 40-cm astrograph of the Sternberg Astronomical Institute(Lomonosov Moscow University) in 1976–1994 and digitized with a resolution of 2400 dpi, we discovered and studied 275 new variable stars. We present the list of our new variables with all necessary information concerning their brightness variations. As in our earlier studies, the new discoveries show a rather large number of high-amplitude Delta Scuti variables, predicting that many stars of this type remain not detected in the whole sky. We also performed automated classification of the newly discovered variable stars based on the Random Forest algorithm. The results of the automated classification were compared to traditional classification and showed that automated classification was possible even with noisy photographic data. However, further improvement of automated techniques is needed, which is especially important when considering the very large numbers of new discoveries expected from all-sky surveys.     

Pulsation and Long-Term Variability of the High-Amplitude δ Scuti Star AD Canis Minoris

Time-series photometry was made for the large-amplitude δ Scuti star AD CMi in 2005 and 2006. High-quality photometric data provided in the literature were used to analyze the pulsation of the star, with the derived multiple frequencies fitted to our new data. Besides the dominant frequency and its harmonics, one low frequency (2.27402 c d -1) is discovered, which provides a reasonable interpretation for the long-noticed luminosity variation at the maximum and minimum light. Combining the nine new times of light maxima determined from the new data with the 64 times collected from the literature, we analyzed the long-term variability of AD CMi with the O - C technique. The results provide the updated value of period of 0.122974478 days, and seem to be in favor of the model of combination of the evolutionary effect and light-time effect of a binary system, of which some parameters are hereby deduced.     

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.     

Lunar-based Ultraviolet Telescope study of the well-known Algol-type binary TW Dra

By using the Lunar-based Ultraviolet Telescope(LUT) from 2014 December 2 to December 4,the first near-UV light curve of the well-known Algol-type binary TW Dra is reported,which is analyzed with the 2013 version of the W-D code.Our solutions confirmed that TW Dra is a semi-detached binary system where the secondary component fills its Roche lobe.The mass ratio and a high inclination are obtained(q = 0.47,i = 86.68°).Based on 589 available data spanning more than one century,the complex period changes are studied.Secular increase and three cyclical changes are found in the corresponding orbital period analysis.The secular increase changes reveal mass transfer from the secondary component to the primary one at a rate of 6.8 × 10~(-7)M_⊙yr~(-1).One large cyclical change of 116.04 yr may be caused by disturbance of visual component ADS 9706 B orbiting TW Dra(ADS 9706A),while the other two cyclical changes with shorter periods of 22.47 and 37.27 yr can be explained as the result of two circumbinary companions that are orbiting around TW Dra,where the two companions are in simple 3 :5 orbit-rotation resonances.TW Dra itself is a basic binary in a possible sextuple system with the configuration(1 + 1) +(1 + 1) +(1 + 1),which further suggests that multiplicity may be a fairly common phenomenon in close binary systems.