Multi-band photometric observations of eleven totally eclipsing contact binaries were carried out. Applying the Wilson-Devinney program, photometric solutions were obtained. There are two W-subtype systems, which are CRTS J133031.1+161202 and CRTS J154254.0+324652, and the rest systems are A-subtype systems. CRTS J154254.0+324652 has the highest fill-out factor with 94.3$\%$, and the lowest object is CRTS J155009.2+493639 with only 18.9$\%$. The mass ratios of the eleven systems are all less than 0.1, which means that they are extremely low mass ratio binary systems. We performed period variation investigation and found that the orbital periods of three systems decrease slowly, which may be caused by the angular momentum loss, and of six systems increase slowly, which indicates that the materials may transfer from the secondary component to the primary component. LAMOST low$-$resolution spectra of four objects were analyzed, and using the spectral subtraction technique, H$α$ emission line was detected, which means that the four objects exhibit chromospheric activity. In order to understand their evolutionary status, the mass-luminosity and mass-radius diagrams were plotted. The two diagrams indicate that the primary component is in the main sequence evolution stage, and the secondary component is above TAMS, indicating that they are over-luminous. To determine whether the eleven systems are in stable state, the ratio of spin angular momentum to orbital angular momentum ($J_{s}/J_{o}$) and the instability parameters were calculated, and we argued that CRTS J234634.7+222824 is on the verge of a merger.
M-dwarfs in extremely wide binary systems are very rare, and may thus have different formation processes from those found as single stars or close binaries in the field. In this paper we search for close companions to a new sample of 36 extremely wide M-dwarf binaries, covering a spectral type range of M1 to M5 and a separation range of 600 - 6500 AU. We discover 10 new triple systems and one new quadruple system. We carefully account for selection effects including proper motion, magnitude limits, the detection of close binaries in the SDSS, and other sample biases. The bias-corrected total h…
The stability of mass transfer is important in the formation of contact binaries from detached binaries when the primaries of the initially detached binaries fill their Roche lobes. Using Eggleton's stellar evolution code, we investigate the formation and the short-period limit of contact binaries by considering the effect of the instability of mass transfer. It is found that with decreasing initial primary mass from 0.89M$_{\rm \odot}$ to 0.63M$_{\rm \odot}$, the range of the initial mass ratio decreases for detached binaries that experience stable mass transfer and evolve into contact. If th…
The detached-binary channel is an important channel for the formation of contact binaries, according to which a detached binary might evolve into contact by evolutionary expansion of the components, or angular momentum loss through the effect of magnetic braking (MB). We have carried out a detailed binary population synthesis (BPS) study of this channel, and obtained the parameter regions for detached binaries to evolve into contact. Combining the observations from the $\emph{Kepler}$ satellite with our results, we found that the ratio of the birth rate of the progenitors of contact binaries t…
The period changes of contact binaries obtained by the analysis of eclipse minima timing are found mostly chaotic in nature. However, they are representable by a few cyclic changes superposed on a secular change. The cyclic changes are caused most probably by the third components revolving around the contact binaries. Some typical examples of the period changes of contact binaries are presented in the present contribution.
Data from the VSX, SDSS DR12, and Gaia DR2 catalogs were combined in order to explore the observed temperature distribution of known contact binaries. Color-temperature relations were applied to calculate the effective temperatures of approximately 20000 binaries and a temperature distribution was built using the results with a precision better than 160 K. The temperature distribution shifts to higher temperatures when increasing the distance of the observed objects. The distribution contains a a previously detected bump in the 6000-7000 K range. It is shown that this second maximum is caused …
High precision CCD observations of six totally eclipsing contact binaries were presented and analyzed. It is found that only one target is an A-type contact binary (V429 Cam), while the others are W-type contact ones. By analyzing the times of light minima, we discovered that two of them exhibit secular period increase while three manifest long-term period decrease. For V1033 Her, a cyclic variation superimposed on the long-term increase was discovered. By comparing the Gaia distances with those calculated by the absolute parameters of 173 contact binaries, we found that Gaia distance can be a…
The photometric and spectroscopic investigations of ten contact binaries were presented for the first time. It is discovered that the mass ratios of all the ten targets are smaller than 0.15, they are extremely low mass ratio contact binaries. Seven of them are deep contact binaries, two are medium contact binaries, while only one is a shallow contact system. Five of them show O'Connell effect, and a dark spot on one of the two components can lead to a good fit of the asymmetric light curves. The orbital period studies of the ten binaries reveal that they all exhibit long-term period changes, …
We performed new photometric observations for two contact binaries (i.e., CRTS J025408.1+265957 and CRTS J012111.1+272933), which were observed by the 1.0-m telescope at Xingjiang Astronomical Observatory. From our light curves and several survey data, we derived several sets of photometric solutions. We found that CRTS J025408.1+265957 and CRTS J012111.1+272933 were Aand W-type W UMa, respectively. The results imply that the spot migrates or disappears in two contact binaries, which were identified by chromospheric activity emissions (e.g. Hα emission) from LAMOST spectra. From the O-C curves…
We present the first light curve solution of 6 contact binary systems which are chosen from the ASAS catalog. The photometric elements and the estimated absolute parameters of all systems are obtained with the light curve analyses. We calculated the values of degree of contact for the systems. The location of the targets on the Hertzsprung-Russell diagram and the mass-radius plane is compared to the other well-known contact binaries and the evolutionary status of the systems are also discussed.
Recently, our understanding of the origin of W UMa-type contact binaries has become clearer. Initial masses of their components were successfully estimated by Yıldız and Doğan using a new method mainly based on observational properties of overluminous secondary components. In this paper, we continue to discuss the results and make computations for age and orbital evolution of these binaries. It is shown that the secondary mass, according to its luminosity, also successfully predicts the observed radius. While the current mass of the primary component is determined by initial masses, the curren…
This work describes the analysis of 64 early-type, massive contact or near-contact eclipsing systems from the Large Magellanic Cloud discovered by the OGLE-III survey. It presents the determination of the period-luminosity-colour relation followed by these objects, that is different from the one previously known for late-type W UMa stars. The relation for massive stars has a significantly steeper dependence on the colour, which is related to a much higher bolometric correction, however it is shallower in the period term. This leads to the conclusion, that the relation for the total population …
The period distribution of contact binaries exhibits a very sharp short period cut-off at 0.22 days. In order to provide valuable information on this short period limit, we observed ten totally eclipsing contact binaries with orbital periods near this cut-off. By detailed analysis using W-D code, we determined that two of these systems are A-subtype contact binaries while the others are W-subtype contact binaries and all the targets show shallow contact configurations. Half of the targets exhibit stellar spot activity and four of them have third light. A statistical work on well studied USPCBs…
In this study, we determined the physical parameters of W UMa type contact binaries and its stability of mass transfer with different stellar mass ranges over a broad space by applying the basic dynamical evolution equations of the W UMa type contact binaries using accretor and donor masses between 0.079 and 2.79 $M_{\odot}$. In these systems, we have studied the three sub-classes of the W UMa system such as A-, B- and W-type of W UMa contact binaries using the initial and final mass ranges and we investigated different stellar and orbital parameters for the sub-classes of W UMa systems. We ex…
The only well-studied red nova progenitor (V1309 Sco) was a contact binary with a 1.4-day period. The prospects for searching for similar systems, as well as stellar merger candidates in general, are explored in this work. The photospheric temperatures of 128 variables with periods P = 1.1 - 1.8 d classified as W UMa-type binaries are calculated using their colors listed in the SDSS catalog. A selection of 15 contact binaries with similar temperatures and periods as the V1309 Sco progenitor is thus compiled. The Kepler Eclipsing Binary Catalog is used to analyse systems with eclipse timing var…
We present the spectroscopic orbits of eleven nearby, mid-to-late M dwarf binary systems in a variety of configurations: two single-lined binaries (SB1s), seven double-lined binaries (SB2s), one double-lined triple (ST2), and one triple-lined triple (ST3). Eight of these orbits are the first published for these systems, while five are newly identified multiples. We obtained multi-epoch, high-resolution spectra with the TRES instrument on the 1.5m Tillinghast Reflector at the Fred Lawrence Whipple Observatory located on Mt. Hopkins in AZ. Using the TiO molecular bands at 7065 -- 7165 Angstroms,…
[Abridged] We test the evolutionary model of cool close binaries on the observed properties of near contact binaries (NCBs). Those with a more massive component filling the Roche lobe are SD1 binaries whereas in SD2 binaries the Roche lobe filling component is less massive. Our evolutionary model assumes that, following the Roche lobe overflow by the more massive component (donor), mass transfer occurs until mass ratio reversal. A binary in an initial phase of mass transfer, before mass equalization, is identified with SD1 binary. We show that the transferred mass forms an equatorial bulge aro…
In this paper, we present the first light curve synthesis and orbital period change analysis of nine contact binaries around the short period limit. It is found that all these systems are W-subtype contact binaries. One of them is a medium contact system while the others are shallow contact ones. Four of them manifest obvious O'Connell effect explained by a dark spot or hot spot on one of the component stars. Third light was detected in three systems. By investigating orbital period variations, we found that four of the targets display a secular period decrease while the others exhibit a long-…
Extremely Low Mass Ratio Contact Binaries. II. The First Photometric and Spectroscopic Investigations of Six Systems with Orbital Periods Longer than 0.5 days
We present the high precession photometric studies in V band and spectroscopic studies centered around H-alpha line for two extreme mass-ratio short period contact binaries ASAS J082243+1927.0 (V1) and ASAS J085710+1856.8 (V2). The variables in study are in the direction of open cluster Praesepe. From the light curve analysis V1 was found to be a low mass-ratio over-contact binary of A-type, with a mass ratio q 0.121 and fill-out factor f 72%, and V2 was found to be a low mass contact binary of W-type, with a mass-ratio q 1.29 and fill-out factor f 11% (marginal contact). The study of H-alpha …
Close detached binaries were theoretically predicted to evolve into contact by three subtypes of case A binary evolution: case AD, AR, and AS, which correspond to the formation of contact during dynamic-, thermal-, and nuclear-timescale mass transfer phase, respectively. It is unclear, however, what is the difference between contact binaries in these subtypes, and whether all of these subtypes can account for the formation of observed W UMa binaries. Using Eggleton's stellar evolution code with the nonconservative assumption, I obtained the low-mass contact binaries produced by case AD, AR, an…
Binary and multiple stellar systems are numerous in our solar neighborhood with 80 per cent of the solar-type stars being members of systems with high order multiplicity. The Contact Binaries Towards Merging (CoBiToM) Project is a programme that focuses on contact binaries and multiple stellar systems, as a key for understanding stellar nature. The goal is to investigate stellar coalescence and merging processes, as the final state of stellar evolution of low-mass contact binary systems. Obtaining observational data of approximately 100 eclipsing binaries and multiple systems and more than 400…
The energy transfer of W UMa contact binaries and its effects on the secondary in W UMa contact binaries are investigated. Relations are given between the mass ratio (q) and the relative energy transfer rates, i.e. U1, the ratio of the transferred luminosity to the surface luminosity of the primary and U2, the ratio of the transferred luminosity to the nuclear luminosity of the secondary. The theoretical curves(U1 vs q and U2 vs q) are derived. Although these curves can reflect the distribution of U1 vs q and U2 vs q, some observational systems are significantly deviated from these curves. It …
By analyzing two sets of complete $BVR_cI_c$ light curves of V342 UMa and three sets of complete $BVR_cI_c$ light curves of V509 Cam, we determined that the two systems are both W-subtype contact binaries and that V342 UMa shows a shallow contact configuration, while V509 Cam exhibits a medium contact configuration. Since 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 pe…
Possible M-type contact binaries were investigated by selecting W UMa-type variables with orbital periods below the 0.22-day cutoff. Gaia parallaxes were combined with Gaia and 2MASS photometry to obtain G and J-band absolute magnitudes of 674 red variable stars catalogued as contact binaries in the VSX database. The absolute magnitude of main sequence cool dwarfs varies strongly with spectral type, which was used to create a selection of 218 systems with primaries potentially of spectral types M0-M3. Lightcurves of the 46 systems with lowest near-infrared luminosities were inspected individua…
The two objects 1SWASP J150822.80-054236.9 and 1SWASP J160156.04+202821.6 were initially detected from their SuperWASP archived light curves as candidate eclipsing binaries with periods close to the short-period cut-off of the orbital period distribution of main sequence binaries, at ~0.2 d. Here, using INT spectroscopic data, we confirm them as double-lined spectroscopic and eclipsing binaries, in contact configuration. Following modelling of their visual light curves and radial velocity curves, we determine their component and system parameters to precisions between ~2 and 11%. The former sy…
W UMa-type contact binaries belong to close binary systems whose components exactly overflow their Roche lobes and share a common convective envelope (CCE). In the last twenty years, the long-term variations of their orbital periods have been thought to depend on several mechanisms. Now, we suggest a new mechanism: CCE-dominated mechanism. The CCE-dominated mechanism is found based on our numerical result, especially at high mass ratios, that the orbital periods (P) of contact binaries change very much with their fill-out factors (f). Because f is taken as a measurement of the thickness of CCE…
Ultra-short orbital period contact binaries (Porb < 0.26 d) host some of the smallest and least massive stars. These systems are faint and rare, and it is believed that they have reached a contact configuration after several Gyrs of evolution via angular momentum loss, mass transfer and mass loss through stellar wind processes. This study is conducted in the frame of Contact Binaries Towards Merging (CoBiToM) Project and presents the results from light curve and orbital analysis of 30 ultra-short orbital period contact binaries, with the aim to investigate the possibility of them being red nov…
Searching for Contact Binaries with LAMOST and TESS
Xinjiang Astronomical Observatory, Chinese Academy of Sciences（中国科学院新疆天文台）；School of Astronomy and Space Science, University of Chinese Academy of Sciences（中国科学院大学天文学与空间科学学院）；Department of Astronomy, Xiamen University（厦门大学天文学系）；College of Physics and Information Engineering, Quanzhou Normal University（泉州师范学院物理与信息工程学院）
We present new, high-quality multicolor observations of four recently discovered contact binaries: 1SWASP J064501.21+342154.9, 1SWASP J155822.10-025604.8, 1SWASP J212808.86+151622.0, and UCAC4 436-062932, and analyze their light curves to determine orbital and physical parameters using the modeling program of G. Djurašević. In the absence of spectroscopic observations, the effective temperatures of the brighter components are estimated from the color indices, and the mass ratios are determined with the q-search method. The analysis shows that all four systems are W UMa type binaries in shallow…
We present a study on low-mass contact binaries (LMCB) with orbital periods shorter than 0.3 days and total mass lower than about 1.4 solar mass. We show that such systems have a long pre-contact phase, which lasts for 8-9 Gyrs, while the contact phase takes only about 0.8 Gyr, which is rather a short fraction of the total life. With low mass transfer rate during contact, moderate mass ratios prevail in LMCBs since they do not have enough time to reach extreme mass ratios often observed in higher mass binaries. During the whole evolution both components of LMCBs remain within the MS band. The …
We present an extensive analysis of new light and radial-velocity (RV) curves, as well as high-quality broadening-function (BF) profiles of twelve binary systems for which a contact configuration with large temperature differencies between components has been reported in the literature. We find that six systems (V1010 Oph, WZ Cyg, VV Cet, DO Cas, FS Lup, V747 Cen) have near-contact configurations. For the remaining systems (CX Vir, FT Lup, BV Eri, FO Hya, CN And, BX And), our solutions of the new observations once again converge in a contact configuration with large temperature differencies be…
We carried out high-precision photometric observations of three eclipsing ultrashortperiod contact binaries (USPCBs). Theoretical models were fitted to the light-curves by means of the Wilson-Devinney code. The solutions suggest that the three targets have evolved to a contact phase. The photometric results are as follows: a) 1SWASP J030749.87-365201.7, q=0.439\pm0.003, f=0.0\pm3.6%; b) 1SWASP J213252.93-441822.6, q=0.560\pm0.003, f=14.2\pm1.9%; c) 1SWASP J200059.78+054408.9, q=0.436\pm0.008, f=58.4\pm1.8%. The light curves show O'Connell effects, which can be modeled by assumed cool spots. Th…
We first discuss a large set of evolutionary calculations of close binaries with a B-type primary at birth and with a period such that the Roche lobe overflow starts during the core hydrogen burning phase of the primary (intermediate mass and massive case A binaries). The evolution of both components is followed simultaneously allowing us to check for the occurrence of contact binaries. We consider various models to treat a contact system and the influence of these models on the predicted Algol-type system population is investigated. We critically discuss the available observations of Algol-ty…
Up to present date, no circumbinary planet around contact binaries were discovered neither by transit method nor by the minima times variation, although they are known having third component stars around. We thus ask: where are the circumbinary planets of contact binaries? By considering the physical and geometrical parameters we simulated the light curves of contact binaries with possible transiting circumbinary jovian planets. It seems either the circumbinary jovian planets are not formed around contact binaries, probably due to dynamical effects of the binary and third component stars, or t…
In this work, we aimed to derive the $gri$-band period-luminosity (PL) and period-luminosity-color (PLC) relations for late-type contact binaries, for the first time, located in the globular clusters, using the homogeneous light curves collected by the Zwicky Transient Factory (ZTF). We started with 79 contact binaries in 15 globular clusters, and retained 30 contact binaries in 10 globular clusters that have adequate number of data points in the ZTF light curves and unaffected by blending. Magnitudes at mean and maximum light of these contact binaries were determined using a fourth-order Four…
A set of 27 evolutionary models of cool close binaries was computed under the assumption that their evolution is influenced by the magnetized winds. Initial periods of 1.5, 2.0 and 2.5 d were considered. For each period three values of 1.3, 1.1 and 0.9 solar mass were taken as the initial masses of the more massive components. Here the results of the computations of the first evolutionary phase are presented, which starts from the initial conditions and ends when the more massive component reaches its critical Roche lobe. In all considered cases this phase lasts for several Gyr. For binaries w…
We investigated the statistical properties of both cool and hot starspots in eclipsing binary stars. The starspot and binary parameters for contact and semi-detached systems were collected from literature, which were determined on the basis of synthetic light-curve analysis. We examined associations between these parameters. As a result, the cool spots in W-type binaries show properties similar to those of sunspots and starspots generated by dynamos, which differs from those of the cool spots in A-type binaries. The properties of hot spots also differ between the W- and A-type samples. From th…
Contact binary star systems represent the long-lived penultimate phase of binary evolution. Population statistics of their physical parameters inform understanding of binary evolutionary pathways and end products. We use light curves and new optical spectroscopy to conduct a pilot study of ten (near-)contact systems in the long-period ($P$>0.5 d) tail of close binaries in the Kepler field. We use PHOEBE light curve models to compute Bayesian probabilities on five principal system parameters. Mass ratios and third-light contributions measured from spectra agree well with those inferred from the…
We used the 50 cm Binocular Network (50BiN) telescope at Delingha Station (Qinghai Province) of Purple Mountain Observatory (Chinese Academy of Sciences) to obtain simultaneous $V$- and $R$-band observations of the old open cluster NGC 188. Our aim was a search for populations of variable stars. We derived light-curve solutions for six W Ursae Majoris (W UMa) eclipsing-binary systems and estimated their orbital parameters. The resulting distance to the W UMas is independent of the physical characteristics of the host cluster. We next determined the current best period--luminosity relations for…
The majority of close massive binary stars with initial periods of a few days experience a contact phase, in which both stars overflow their Roche lobes simultaneously. We perform the first dedicated study of the evolution of massive contact binaries and provide a comprehensive prediction of their observed properties. We compute 2790 detailed binary models for the Large and Small Magellanic Clouds each, assuming a conservative mass transfer. The initial parameter space for both grids span total masses from 20 to 80$\,\textrm{M}_{\odot}$, orbital periods of 0.6 to 2 days and mass ratios of 0.6 …
A sample of 542 eclipsing binaries (EBs) with periods shorter than 2 d were selected from the Microlensing Observations in Astrophysics (MOA) EB catalogue (Li et al. 2017) for eclipse-time variation analysis. For this sample we were able to obtain the time series from MOA-II that span 9.5yr. We discovered 91 EBs, out of the 542 EBs, with detected light-travel-time effect signals suggesting the presence of tertiary companions of orbiting periods from 250 d-28 yr. The frequency of EBs with tertiary companions in our sample increases as the period decreases and reaches a value of 0.65 for contact…
We report on a study of eclipse timing variations in contact binary systems, using long-cadence lightcurves in the Kepler archive. As a first step, 'observed minus calculated' (O-C) curves were produced for both the primary and secondary eclipses of some 2000 Kepler binaries. We find ~390 short-period binaries with O-C curves that exhibit (i) random-walk like variations or quasi-periodicities, with typical amplitudes of +/- 200-300 seconds, and (ii) anticorrelations between the primary and secondary eclipse timing variations. We present a detailed analysis and results for 32 of these binaries …
The time-series component of WISE is a valuable resource for the study of variable objects. We present an analysis of an all-sky sample of ~450,000 AllWISE+NEOWISE infrared light curves of likely variables identified in AllWISE. By computing periodograms of all these sources, we identify ~56,000 periodic variables. Of these, ~42,000 are short-period (P<1 day), near-contact or contact eclipsing binaries, many of which are on the main sequence. We use the periodic and aperiodic variables to test computationally inexpensive methods of periodic variable classification and identification, utilizing…
