Contact Binary Stars Research Articles

Origin of the orbital period change in contact binary stars

The evolution of contact binary star systems in mass asymmetry (transfer) coordinate is considered. The orbital period changes are explained by an evolution in mass asymmetry towards the symmetry (symmetrization of binary system). It is predicted that decreasing and increasing orbital periods are related, respectively, with the nonoverlapping and overlapping stage of the binary star during its symmetrization. A huge amount of energy [Formula: see text][Formula: see text]J is converted from the potential energy into internal energy of the stars during the symmetrization. As shown, the merger of stars in the binary systems, including KIC 9832227, is energetically an unfavorable process. The sensitivity of the calculated results to the values of total mass and orbital angular momentum is analyzed.

First photometric investigations of three eclipsing binaries: AST19571, AST21541, and AST38503

AST3-1 is the second-generation optical photometric telescope at Dome A in Antarctica. In this study, photometric solutions of three eclipsing binaries comprising AST19571, AST21541, and AST38503 were determined for the first time using the light curves obtained with AST3-1. The light curves for the three binaries in the Galactic disk field were analyzed with the Wilson–Devinney method. We found that AST19571 and AST21541 are intermediate-contact binary systems with fill-out factors of f=39.9(±5.4)% and 36.4( ± 4.7) %, respectively, and their mass ratios were determined as q=0.275(±0.0034) and 0.25( ± 0.0024). AST38503 was shown to be a deep-contact binary system with a degree of contact of f=66(±33)% and a mass ratio of q=0.314(±0.03). Some light minimum times were derived for the three contact binary stars. The results showed that the period of AST19571 is increasing at a rate of dp/dt=+4.71×10−7. This increase in the period could be explained by mass transfer between the components. The absolute parameters were estimated for the components of the three binaries.

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 Ic bands of the total-eclipsing 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 dP/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 DR2, absolute parameters were derived as M1 = 1.20 M⊙, M2 = 0.23 M⊙, R1 = 1.36 R⊙ and R2 = 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.

A new study of the variable star population in the Hercules globular cluster (M13; NGC 6205)★

We present the results from $VI$ CCD time-series photometry of the globular cluster M13 (NGC 6205). From the Fourier decomposition of the light curves of RRab and RRc stars we found an average metallicity of [Fe/H]zw = -1.58 $\pm$ 0.09. The distance to the cluster was estimated as 7.1 $\pm$ 0.1 kpc from independent methods related to the variable star families RR Lyrae, SX Phe and W Virginis, from the luminosity of the theoretical ZAHB and from the orbit solution of a newly discovered contact binary star. The RR Lyrae pulsation modes are segregated by the red edge of the first overtone instability strip in this OoII type cluster. A membership analysis of 52,800 stars in the field of the cluster is presented based on \textit{Gaia}-DR2 proper motions which enabled the recognition of 23,070 likely cluster members, for 7,630 of which we possess $VI$ photometry. The identification of member stars allowed the construction of a clean CMD and a proper ZAHB and isochrone fitting, consistent with a reddening, age and distance of 0.02 mag, 12.6 Gyrs and 7.1 kpc respectively. We report seven new variables; one RRc, two SX Phe stars, three SR and one contact binary. V31 presents double-mode nature and we confirm V36 as RRd. Fifteen variable star candidates are also reported. The analysis of eighteen stars in the field of the cluster, reported as RR Lyrae from the $Gaia$-DR2 data base reveals that at least seven are not variable. We noted the presence of a high velocity star in the field of the cluster.

Photometric study of contact binary star MW And

The Tarleton Observatory’s 0.8m telescope and CCD photometer were used to obtain 1298 observations of the short period eclipsing binary star MW And. The observations were obtained in Johnson’s BVR filters. The light curves show that MW And is an eclipsing binary star with a period of 0.26376886 days. Further analysis showed that the period of MW And is changing at the rate of 0.17sec/year. The photometric solutions were obtained using the 2015 version of the Wilson-Devinney model. The solutions show that MW And is an eclipsing binary star of W UMa type. Our analysis suggests that the system has a light curve of W-subtype contact system. Its spectral type of K0/K1, as estimated from its color, places it in the Zero-Age contact zone of the period-spectral type diagram. Luminosity from the solutions indicates that it is a double-line spectroscopic system and therefore, spectroscopic observations are recommended for further detail study.

Infrared spectroscopy of the merger candidate KIC 9832227

Context. It has been predicted that the object KIC 9832227 – a contact binary star – will undergo a merger in 2022.2 ± 0.7. We describe the near-infrared (NIR) spectrum of this object as an impetus to obtain pre-merger data. Aims. We aim to characterise (i) the nature of the individual components of the binary and (ii) the likely circumbinary environment, so that the merger – if and when it occurs – can be interpreted in an informed manner. Methods. We use infrared (IR) spectroscopy in the wavelength range 0.7–2.5 μm, to which we fit model atmospheres to represent the individual stars. We use the binary ephemeris to determine the orbital phase at the time of observation. Results. We find that the IR spectrum is best fitted by a single component with effective temperature 5920 K, log[g] = 4.1, and solar metallicity, consistent with the fact that the system was observed at conjunction. Conclusions. The strength of the IR H lines is consistent with a high value of logg, and the strength of the Ca II triplet indicates the presence of a chromosphere, as might be expected from rapid stellar rotation. The He I absorption we observe likely arises in He excited by coronal activity in a circumstellar envelope, suggesting that the weakness of the Ca II triplet is also likely chromospheric in origin.

Gas–Dynamical Features of the Envelopes of Contact Binary Stars

The results of three-dimensional numerical simulations of the gaseous envelope of a contact binary star with parameters similar to those of SV Cen are presented. The outflow of matter from the vicinity of the Lagrange point L2 leads to the formation of a disk-like common envelope with a radius of order three times the component separation. The characteristics of this envelope and its structure and dynamics are discussed, as well as possible observational manifestations of such an envelope.

TYC 1337-1137-1 and TYC 3836-0854-1: Two Low-mass Ratio, Deep Overcontact Systems Near the End Evolutionary Stage of Contact Binaries

New high-precision CCD photometric light curves of two contact binary stars, TYC 1337-1137-1 and TYC 3836-0854-1, are displayed and analyzed by using the Wilson–Devinney (W–D) program. The light curve solutions show that both of them are low-mass ratio, deep overcontact binary systems with a mass ratio of q = 0.1716 ± 0.0010 and a high fillout factor of f = 76.0 ± 2.9% for TYC 1337-1137-1, and q = 0.1900 ± 0.0032 and f = 79.4 ± 7.9% for TYC 3836-0854-1, respectively. These results indicate that they are near the end evolutionary stage of contact binaries. The absolute parameters were calculated by using the new method of mass–radius relationship (0.238 ± 0.009 M⊙ and 1.386 ± 0.050 M⊙ for TYC 1337-1137-1, 0.228 ± 0.014 M⊙ and 1.20 ± 0.07 M⊙ for TYC 3836-0854-1, respectively). The preliminary orbital period analysis suggests that long-term period increases exist for both of them, which may be interpreted in two possible ways. A first possibility is mass transfer conservation from the less massive component to the more massive one leading to an orbital period increase. In this case, when their orbital angular momentum is less than three times the total spin angular momentum, they may evolve into a rapidly rotating single star. A second possibility is that the parabolic variation in the (O − C) diagram is only a part of a long-period cyclic change caused by a potential third body. In future, more high-precision observations of these two binaries are needed to confirm the form of orbital period changes.

Absolute-magnitude Calibration for W UMa-type Systems Based on Gaia Data*

Abstract Tycho-Gaia Astrometric Solution (TGAS) parallax data are used to determine absolute magnitudes M V for 318 W UMa-type (EW) contact binary stars. A very steep (slope ≃ −9), single-parameter ( ), linear calibration can be used to predict M V to about 0.1–0.3 mag over the whole range of accessible orbital period, days. A similar calibration for the most common systems with days predicts M V values to about 0.06–0.16 mag. For orbital period values both shorter and longer than the central range, the period dependence is respectively steeper and shallower, i.e., the binaries are fainter in M V than predicted by the whole-range linear law. The steepness of the relation for short-period systems implies important consequences for the detectability of the faintest binaries, defining the short-period cut-off of the period distribution. Although the scatter around the linear -fit is fairly large (0.2–0.4 mag), the current data do not support the inclusion of a color term in the calibration.

MULTI-FILTER LIGHT CURVES OF 29 VERY SHORT PERIOD CANDIDATE CONTACT BINARIES

ABSTRACT Light curves of 26 probable contact binary stars are made available, from a list of candidates with the shortest periods known. This is supplemented by sets of light curves of three previously studied systems. Photometry was obtained in the Johnson UBV, Cousins RI system. All stars but one were observed in four wavebands, either UBV R C or BV ( RI ) C , depending on brightness. Tentative spectral classifications are given for 23 of the stars. Effective temperatures are derived from infrared and optical photometric indices, and from spectral types. These are generally in good agreement. The multicolor photometry, spectral typing, and estimated effective temperatures can be used to model these systems in detail. A preliminary study, based on Fourier coefficients of the light curves, suggests that all the systems are indeed eclipsing stars, with all but a handful probably in contact configurations.

The active W UMa type binary star V781 Tau revisited

In this paper, new determined BVR_cI_c light curves and radial velocities of V781 Tau are presented. By analyzing the light curves and radial velocities simultaneously, we found that V781 Tau is a W-subtype medium contact binary star with a mass ratio of q=2.207+-0.005 and a contact degree of f=21.6(+-1.0)%. The difference between the two light maxima was explained by a dark spot on the less massive primary component. The orbital period change of V781 Tau was also investigated. A secular decrease at a rate of $-6.01(+-2.28)*10^{-8} d/yr and a cyclic modulation with a period of 44.8+-5.7 yr and an amplitude of 0.0064+-0.0011 day were discovered. The continuous period decrease may be caused by angular momentum loss due to magnetic stellar wind. Applegate mechanism failed to explain the cyclic modulation. It is highly possible that the cyclic oscillation is the result of the light travel time effect by a third companion.

SuperWASP J015100.23-100524.2: A SPOTTED SHALLOW-CONTACT BINARY BELOW THE PERIOD LIMIT

SuperWASP J015100.23-100524.2 (hereafter J015100) is an eclipsing binary with an orbital period of 0(d).2145 that is below the short-period limit of contact binary stars. Complete light curves of J015100 in B, V, R, and I bands are presented and are analyzed with the Wilson-Devinney method. It has been discovered that J015100 is a shallow-contact binary (f = 14.6(+/- 2.7)%) with a mass ratio of 3.128. It is a W-type contact binary where the less massive component is about 130 K hotter than the more massive one. The asymmetries of light curves are explained as one dark spot on the more massive component. The detection of J015100 as a contact binary below the period limit suggests that contact binaries below this limit are not rapidly destroyed. This shallow-contact system may be formed from a detached short-period binary similar to DV Psc (Sp. = K4/K5; P = 0(d).30855) via orbital shrinkage due to angular momentum loss through magnetic stellar wind.

The WFCAM multiwavelength Variable Star Catalog(Corrigendum)

Stellar variability in the near-infrared (NIR) remains largely unexplored. The exploitation of public science archives with data-mining methods offers a perspective for the time-domain exploration of the NIR sky. We perform a comprehensive search for stellar variability using the optical-NIR multi-band photometric data in the public Calibration Database of the WFCAM Science Archive (WSA), with the aim of contributing to the general census of variable stars, and to extend the current scarce inventory of accurate NIR light curves for a number of variable star classes. We introduce new variability indices designed for multi-band data with correlated sampling, and apply them for pre-selecting variable star candidates, i.e., light curves that are dominated by correlated variations, from noise-dominated ones. Pre-selection criteria are established by robust numerical tests for evaluating the response of variability indices to colored noise characteristic to the data. We find 275 periodic variable stars and an additional 44 objects with suspected variability with uncertain periods or apparently aperiodic variation. Only 44 of these objects had been previously known, including 11 RR~Lyrae stars in the outskirts of the globular cluster M3 (NGC~5272). We provide a preliminary classification of the new variable stars that have well-measured light curves, but the variability types of a large number of objects remain ambiguous. We classify most of the new variables as contact binary stars, but we also find several pulsating stars, among which 34 are probably new field RR~Lyrae and 3 are likely Cepheids. We also identify 32 highly reddened variable objects close to previously known dark nebulae, suggesting that these are embedded young stellar objects. We publish our results and all light-curve data as the WFCAM Variable Star Catalog.

SDSS J001641-000925: THE FIRST STABLE RED DWARF CONTACT BINARY WITH A CLOSE-IN STELLAR COMPANION

SDSS J001641-000925 is the first red dwarf contact binary star with an orbital period of 0.19856 days that is one of the shortest known periods among M-dwarf binary systems. The orbital period was detected to be decreasing rapidly at a rate of P similar to 8 s yr(-1). This indicated that SDSS J001641-000925 was undergoing coalescence via a dynamical mass transfer or loss and thus this red dwarf contact binary is dynamically unstable. To understand the properties of the period change, we monitored the binary system photometrically from 2011 September 2 to 2014 October 1 by using several telescopes in the world and 25 eclipse times were determined. It is discovered that the rapid decrease of the orbital period is not true. This is contrary to the prediction that the system is merging driven by rapid mass transfer or loss. Our preliminary analysis suggests that the observed minus calculated (O-C) diagram shows a cyclic oscillation with an amplitude of 0.00255 days and a period of 5.7 yr. The cyclic variation can be explained by the light travel time effect via the presence of a cool stellar companion with a mass of M-3 sin i' similar to 0.14M(circle dot). The orbital separation between the third body and the central binary is about 2.8AU. These results reveal that the rarity of red dwarf contact binaries could not be explained by rapidly dynamical destruction and the presence of the third body helps to form the red dwarf contact binary.

PHOTOMETRIC INVESTIGATION OF THE TOTALLY ECLIPSING CONTACT BINARY V12 IN THE INTERMEDIATE-AGE OPEN CLUSTER NGC 7789

NGC 7789 is an intermediate-age open cluster with an age that is similar to the mean age of contact binary stars. V12 is a bright UMa-type binary star with an orbital period of 0.397 day. The first complete light curves of V12 in V, R, and I bands are presented and analyzed with the W-D (Wilson and Devinney) method. The results shows that V12 is an intermediate-contact binary (f = 43%) with a mass ratio of 3.848, and it is a W-type contact binary where the less massive component is slightly hotter than the more massive one. The asymmetries of the light curves are explained by the presence of a dark spot on the more massive component. The derived orbital inclination (i = 83.6o) indicates that it is a total eclipsing binary, which suggests that the determined parameters are reliable. The orbital period may show a long-term increase at a rate of P = +2.48 x 10-6 days/year that reveals a rapid mass transfer from the less massive component to the more massive one. However, more observations are needed to confirm this conclusion. The presence of an intermediate-contact binary in an intermediate-age open cluster may suggest that some contact binaries have a very short pre-contact timescale. The presence of a third body or/and stellar collision may help to shorten the pre-contact evolution.

The WFCAM multiwavelength Variable Star Catalog

Context. Stellar variability in the near-infrared (NIR) remains largely unexplored. The exploitation of public science archives with data-mining methods offers a perspective for a time-domain exploration of the NIR sky. Aims. We perform a comprehensive search for stellar variability using the optical-NIR multiband photometric data in the public Calibration Database of the WFCAM Science Archive (WSA), with the aim of contributing to the general census of variable stars and of extending the current scarce inventory of accurate NIR light curves for a number of variable star classes. Methods. Standard data-mining methods were applied to extract and fine-tune time-series data from the WSA. We introduced new variability indices designed for multiband data with correlated sampling, and applied them for preselecting variable star candidates, i.e., light curves that are dominated by correlated variations, from noise-dominated ones. Preselection criteria were established by robust numerical tests for evaluating the response of variability indices to the colored noise characteristic of the data. We performed a period search using the string-length minimization method on an initial catalog of 6551 variable star candidates preselected by variability indices. Further frequency analysis was performed on positive candidates using three additional methods in combination, in order to cope with aliasing. Results. We find 275 periodic variable stars and an additional 44 objects with suspected variability with uncertain periods or apparently aperiodic variation. Only 44 of these objects had been previously known, including 11 RR Lyrae stars on the outskirts of the globular cluster M 3 (NGC 5272). We provide a preliminary classification of the new variable stars that have well-measured light curves, but the variability types of a large number of objects remain ambiguous. We classify most of the new variables as contact binary stars, but we also find several pulsating stars, among which 34 are probably new field RR Lyrae, and 3 are likely Cepheids. We also identify 32 highly reddened variable objects close to previously known dark nebulae, suggesting that these are embedded young stellar objects. We publish our results and all light curve data as the WFCAM Variable Star Catalog.

A period study and revised photometric model for the eclipsing binary ZZ Cyg

We present new photometry of the eclipsing binary ZZ Cyg. From all accumulated eclipsing times, we constructed the (O–C) curve, which can be described by a downward parabola with a possible light-time orbit. The period decrease rate is dP/dt=-5.73(±0.18)dyr-1. The modulated period, semi-amplitude and eccentricity for the light-time orbit are Pmod=71.4(±1.1)yr, A=0.0071(±0.0005)day and e=0.420(±0.053), respectively. After removing effects of the magnetic activity, this kind of cyclic oscillation may be attributed to light-time effect via an additional companion. By using the W-D code, the photometric model was updated, which identified that ZZ Cyg is a near-contact binary. We find that a hot spot may occur on the primary that explains the asymmetric light curve. The secular period decrease may possibly cause the fill-out factor of the primary to increase. Finally it will finally fill its Roche lobe. This kind of binary, ZZ Cyg, may evolve into contact binary star.

Evolution of red Nova V4332 Sagittarii remnant

We present the multicolor BV RI photometry and BTA/SCORPIO spectroscopy for the red nova V4332 Sgr, performed in 2005–2012. We have analyzed the behavior of the nova remnant, considering our observations along with all the published observations and archival photographic photometry. The atomic and molecular emission spectra show an exponential weakening. Since 2003, the line fluxes have on the average decreased 30-fold. The continuum of the M-type giant in the spectrum has weakened abruptly between 2006 and 2008, twice in the red and by 4 times in the blue range. The variations in the spectral energy distribution of the stellar continuum after the outburst correspond to a decrease in the surface temperature of the M-type giant by 1000 K. The presence of a faint star of about 20m is possible. The star can be either a member of the system or a field star. It is found that the phenomenon of the red nova in this system is not related with the M-type star. The progenitor of the explosion could be a blue straggler, which has disappeared from the spectral energy distribution after the explosion of 1994. It is most likely that this object was a contact binary system. To explain the “cold explosion” of V4332 Sgr, we have accepted the hypothesis of merging components of a contact binary star in a hierarchical triple or multiple system. There are evidences of dynamical destruction of the outburst remnant and accretion of its matter to the M-type giant. The cause of the red nova phenomenon is thought to be a sudden explosive energy release in the center of a star having a massive envelope, and a subsequent expansion of the envelope in the conditions close to adiabatic. As a result of the explosion, thermal energy reaches the surface of the envelope a year or a few years after the outburst, whereas the envelope already has a large surface area. The cause of the explosion in the center of the star can be both a merger event of the nuclei of two stars in the contact system with a formed common massive envelope and instability in the core of a single massive star. Thus, the red novae can be heterogeneous objects at different evolutionary stages.

Close-in companions to contact binary stars

W UMa-type contact binaries are composed of two late-type main-sequence stars, where both components are filling their critical Roche Lobes and sharing a common convective envelope. Their formation and evolution are unsolved problems in stellar astrophysics. This kind of binary systems have the lowest angular momentum and shortest orbital periods among main-sequence binaries. One of the possibilities for their origin is that the angular momentums of binary stars are transferred from the central binaries to close-in companions. In this paper, we will summarize some of our recent progresses on searching for close-in companions to contact binary stars, including the closest stellar companion to a contact binary at an orbital separation of about 0.8 AU. Then, based on the observational properties of those close-in companions, the formation and the evolution of contact binaries will be discussed.

Analysis of photometric light curves for massive contact binary OB stars. V701 Scorpii

To study the influence of circumstellar gaseous matter on the observed photometric characteristics of early-type, massive contact binaries, we investigated residual curves (difference between the observed and calculated brightnesses as functions of the orbital phase) for the star V701 Scorpii. The residual curves can be used to estimate the influence of gaseous matter in the common envelope on the observed light curves for different phase intervals, and to qualitatively describe the associated distortion of light from the system’s components. Changes of the residual curves from filter to filter indicate the wavelength dependence of the distortion of the light from the components in the circumstellar matter. Differences between the residual curves for different observing epochs testify to time variations in the conditions in the circumstellar matter. We compared the residual curves obtained for different photometric bands and observing epochs using correlation analyses. The distortion of the light from the components of V701 Scorpii in the UV differs from that in the visual and changes in time. This conclusion is supported by the calculated values of the overflow of the first critical Roche lobe by the components.