Properties of Components in Contact Systems

A new sample of contact systems, consisting of more than 100 stars, was created for binaries for which the physical parameters have been determined using both photometric light curves and radial velocity measurements of both components. Properties of components are discussed including their evolutionary status.     

Ten CoRoT eclipsing binaries: Photometric solutions

Ten eclipsing binaries, identified in the scope of the CoRoT Space Mission, were selected for analysis. The photometric light curves were processed and analyzed, resulting in the first study of eclipsing binary candidates with their possible photometric solution, in the context of the above-mentioned Space Mission. The selected targets are detached and overcontact systems, for which we computed 2MASS temperatures, in addition to different physical parameters, including orbital period, orbit inclination angle, and temperatures, radius and luminosity ratios. This study reveals a large diversity of eclipsing binary systems obtained from the CoRoT data.     

A photometric study of two recently discovered,contact binaries-II: UCAC4 479-113658 and UCAC4 479-113711

In a previous paper, we have presented photometric studies of four recently discovered contact binaries (Djurašević, et al., 2016; hereafter Paper I) that were observed by the 1.88 m telescope of the Kottamia Astronomical Observatory (KAO) in Egypt. In this paper we continue studying two more recently discovered, by some of us, contact binaries UCAC4 479-113658 and UCAC4 479-113711, and analyze their light curves to determine orbital and physical parameters using the modeling program of G. Djurašević as in Paper I. The analysis shows that the two systems are W UMa contact binaries of late type main-sequence stars with a bright spot on the secondary less massive cool star of the first system; and spot on each component of the later system. We also conclude that both systems are most likely to be of the A-type class.     

Physical properties of three short period close binaries:KIC 2715417,KIC 6050116 and KIC 6287172

We present the physical parameters of three short period close binaries using data observed from the Kepler Space Telescope. All of these observations were taken in a single bandpass(which approximates the Johnson V-band). Our three systems are KIC 2715417, KIC 6050116 and KIC 6287172. The first system, KIC 2715417, is considered a semi-detached system with the secondary component filling its Roche lobe. The second system, KIC 6050116, is an overcontact system, while the third system, KIC 6287172, belongs to ellipsoidal variables as deduced from the Roche lobe geometry. For photometric analysis, we used the PHOEBE software package, which is based on the Wilson-Devinney code. Due to lack of spectroscopic data, the photometric mass ratios are determined from the analyses of light curves using the q-search method. The absolute parameters are determined using three different methods(Harmanec, Maceroni Van'tVeer and Gazeas Niarchos).     

Photometric analysis of 8 newly discovered short-period eclipsing binaries at Astronomical Observatory at Kolonica Saddle

We present photometric analysis of 8 short-period eclipsing binaries discovered and observed at Astronomical Observatory at Kolonica Saddle between 2007 and 2010 with different instruments. We determined their orbital periods and performed photometric analysis of their light curves. We found that 3 systems are detached binaries, 4 systems are over-contact binaries of W UMa type and one system is semi-detached with the secondary component filling its Roche lobe. Light curves of 2 systems exhibit asymmetries, explained by spot(s) on the surface of the components.     

Star-Spots Studies for Three Short Period RS CVn-Type Binaries

Light curve analysis for three short-period RS CVn-type binaries were performed, using: a) Fourier analysis techniques for light curve changes in the frequency domain; b) photometric curve fit by means of numerical quadratures to develop theoretical light curves appropriate to RS CVn stars. The two methods were applied to the systems ER Vul, BH Vir, and UV Psc. Improved physical and geometrical parameters are found by taking the average of the results measured by the above two methods.     

The Impact of CoRoT on Close Binary Research

The space experiment CoRoT will provide continuous monitoring and high accuracy light curves of about sixty thousand stars. Selected binary systems will be observed in the Additional Program frame as targets of long and continuous pointed observations. Moreover, thousands of new binaries will certainly be detected and hundreds of them will have extremely accurate light curves. This will allow studies of fine effects on the light curves, monitoring of stellar activity and, in combination with ground-based observations, will provide exquisite determination of stellar parameters. Among the new discoveries of interesting systems of special value will be those of low mass binaries.     

Role of the Rossiter-McLaughlin effect in the study of close binaries

This paper is devoted to binary stars belonging to the class of eclipsing-variable systems.Photometric and spectroscopic analysis of eclipses allows us to determine geometric parameters of the orbit and physical characteristics of stellar components as well as inclinations of stellar equators to the orbital plane. Estimations of inclinations can be obtained from measurement of the Rossiter-McLaughlin effect, which is discussed using examples of some eccentric binaries with an anomalous apsidal effect. Our task is to find the complete spectrum of solutions of the equation of apsidal motion, depending on the inclinations of the polar axes of the components to the orbital one for these systems, based on their individual spectroscopic and photometric observational data. The matrix of solutions allows us to select those pairs of polar inclinations that provide agreement with the observational apsidal period.     

Photometric Mass Ratios of Eclipsing Binary Stars

Following a brief history of measurement of eclipsing binary mass ratios from light curves, we show that photometric mass ratios for overcontact and semi-detached binaries are reliable because the relative stellar radii, R/a, are accurately measured and not, as commonly claimed, because of information in the light variation outside eclipse. We explore the accuracy of photometric mass ratios by solving synthetic data of typical precisions for a semi-detached and an overcontact binary for orbital inclinations from 89^∘ down into the partial eclipse range.     

Spot Modelling of ζ Andromedae

The photometric light modulation of ζ Andromedae originates from the distorted geometry of the primary, and additionally, from spots of which parameters (temperature, size, location) are variable in time. We present spot modelling results for six two-colour light curves which show that spots preferably appear on the stellar surface towards the companion star and opposite to it, where the distortion also causes dimming. Therefore, simple fitting of the measured data for the ellipticity effect does not yield correct result. Instead, ellipticity calculated from exact stellar parameters should be removed from the data to get reliable spotted light curves.     

First photometric analysis of the two EW binaries ZTF J214226.88+435827.1 and KAO-EGYPT J214216.38+440015.1

The EW-type eclipsing binaries are strongly interacting systems known to have often both component stars filling their crucial Roche lobes and having a common envelope. We present new BVRI light curves of the eclipsing binaries ZTF J214226.88+435,827.1 (ZTF21+43) and KAO-EGYPT J214216.38+440,015.1 (KAO21+44) based on CCD observations acquired with the 1.88-m Kottamia Astronomical Observatory (KAO) at Newtonian and Cassegrain telescope focus. The modeling results show that these two systems are to be W UMa contact binaries belonging to EW subtypes. All the light curves show the inverse O'Connell effect. We computed new ephemeris for each system using our times of minima and that available in the literature. Using our new times of minima and epochs for both systems from all available observations, the orbital period changes of these structures are studied for our systems. Using the PHOEBE package, a preliminary determination of the two systems' photometric orbital and physical parameters has been present. The positions of the systems were also depicted on the Hertzsprung-Russell (H-R), M-L, and T_eff-L diagrams to test their evolutionary status.     

Disk wind in young binaries and the origin of the cyclic activity of young stars

We present the results of our numerical simulations of the cyclic brightness modulation in young binary systems with eccentric orbits and low-mass secondary components. We suggest that the binary components accrete matter from the remnants of the protostellar cloud, with the main accretor (according to current models) being the low-mass component. The brightness variations of the primary are attributable to the periodic extinction variations on the line of sight caused by the disk wind from the secondary and by the common envelope produced by this wind. The distribution of matter in the envelope was calculated in the ballistic approximation. When calculating the optical effects produced by the dust component of the disk wind, we adopted the dust-to-gas mass ratio of 1:100 characteristic of the interstellar medium and the optical parameters of the circumstellar dust typical of young stars. Our calculations show that the theoretical light curves for binaries with elliptical orbits exhibit a wider variety of shapes than those for binaries with circular orbits. In this case, the parameters of the photometric minima (their depth, duration, and shape of the light curve) depend not only on the disk-wind parameters and the orbital inclination of the binary to the line of sight, but also on the longitude of the periastron. We investigate the modulation of the scattered radiation from the common envelope with orbital phase in the single-scattering approximation. The modulation amplitude is shown to be at a maximum when the system is seen edge-on and to be also nonzero in binaries seen pole-on. We discuss possible applications of the theory to young stellar objects. In particular, several model light curves have been found to be similar to those of candidate FU Orionis stars (FUORs).     

Light curves of gas-eclipsed binary systems

Light curves have been calculated for the model of a binary system consisting of two spherical components, imbedded in a common spherically-symmetric, isotropically-scattering envelope with radially-varying opacity. The periodically-varying screening of stellar radiation by the envelope gives rise to regular light changes, which are similar to stellar eclipses during a superior conjunction of the components and in maxima resemble the light changes due to the reflection effect for Algol-type binaries, whereas for systems with nearly equal luminosities of the components they match light variations, caused by the gravitational distortions of stellar figures.It is shown that the light changes in AO Cas can be interpreted in terms of our model and we propose to call binaries of that type gas-eclipsed variables. The observed light curves RY Gem, RS CVn, VW Cep are compared with the model curves. It is indicated that the light curve of the Algol-type system RY Gem can be interpreted in the framework of the adopted model, provided that stellar eclipses are accompanied by the screening effect of the envelope.Asymmetry, local fluctuations, different widths of minima, and some other peculiarities of the observed light curves are discussed within the context of our model. It can be regarded as a certain optical counterpart of the Roche model, since the isophotes of the envelope resemble the Roche equipotentials in their behaviour.     

Hunting for overlooked eccentric eclipsing binaries from ASAS-3 survey

We present the results of searching for new candidates of eclipsing binaries with eccentric orbits in the ASAS Catalog of Variable Stars (ACVS) using publicly available data from the All Sky Automated Survey (ASAS) and the Transiting Exoplanet Survey Satellite (TESS). Unsupervised machine learning techniques were applied to find anomalies among the light curves of eclipsing binaries. The light curves modeling were performed using JKTEBOP code. The pulsation analysis was done with FAMIAS. We identified 19 new eclipsing binary candidates with non-zero eccentricities in the ACVS, including 10 candidates with eccentricities e ≥ 0.1. Estimates of eccentricities are given. We also report on possible presence of the small-amplitude stellar pulsations at least in two of the reported systems.     

The First Photometric Analyses Of Four New Discovered Ew-Type Eclipsing Binaries: GSC 1848-1264, GSC 0804-0118, GSC 0619-0232 And GSC 2936-0478

Photometric solutions of four new discovered W UMa-type binaries were carried out for the first time by using the 2003 version of the W-D program. It is discovered that all of the four systems are over-contact binaries. Two binaries, GSC 0804-0118 and GSC 2936-0478, are of A-subtype, while two other binaries, GSC 1848-1264 and GSC 0619-0232, are of W-subtype. From our solutions, the fundamental orbital and physical parameters were determined. For GSC 0619-0232 and GSC 2936-0478, the asymmetries of the light curves (i.e., the O'Connell effect) were explained by the presence of dark spots on the more massive components. Our photometric results reveal that GSC 0619-0232 is an important and interesting system. It is a W-type over-contact binary with a low mass ratio of q = 0.100 and a high over-contact degree of f = 93.4%, which suggests that GSC 0619-0232 may be evolved into a single rapid-rotating star.     

Observed photometric peculiarities of six eclipsing binaries with solar-type activity: I

From the observed light curves of six eclipsing binaries with solar-type activity and from the analysis of their period variations some problems in the interpretation of the observations came out: Are these binaries similar to classical RS CVn stars? Is the stellar surface spot coverage the unique interpretation of the observed light curves? Are these systems really linked with W UMa's? In a further study some models will be tempted to try to solve these problems.     

Late-type X-ray Emitting Binaries in the Solar Neighborhood and in Star Forming Regions

We present a spectroscopic and photometric follow-up of binary stars, discovered in a sample of X-ray sources, aimed at a deep characterization of the stellar X-ray population in the solar neighborhood and in Star Forming Regions (SFRs). The sources have been selected from the RasTyc sample, obtained by the cross-correlation between the ROSAT all-sky survey and Tycho catalogues (Guillout et al., 1999). Thanks to the high resolution spectroscopy, we have obtained good radial velocity curves, whose solutions provided us with the mass ratios and minimum masses of the components. We have also obtained an accurate spectral classification with codes specifically developed by us. In addition, we could obtain information on the age of the sources through the Lii-6708 line and on the chromospheric activity level through the Hα line.We show also some results on very young pre-main sequence (PMS) binaries discovered as optical counterparts of X-ray sources in SFRs. The spectroscopic and photometric monitoring has allowed us to determine the orbital and physical parameters and the rotation periods, that are of great importance for testing the models of PMS evolution.     

The common convective envelope model for W Ursae Majoris systems and the analysis of their light curves

The common convective envelope model for W UMa systems is used to analyse the light curves of the sixteen systems with spectroscopic mass ratios. From the derived photometric elements, an indication is found that Binnendijk's W-type systems have only shollow common envelopes, which is therefore suggested to be the cause of the difference between A- and W-type systems. It is also suggested that the structure of many contact binaries permits only a shallow common envelope and that further study of such envelopes will yield the modification in the model required if a closer fit to the W-type light curves is to be obtained.The model is also used with mass ratio as an additional photometric element to analyse the light curve of AW UMa. The solution obtained confirms the remarkably small mass ratio of 0.08 found by Mauder and by Mochnacki and Doughty.Originally presented at the IAU Colloquium No. 16 held at the University of Pennsylvania, Philadelphia, Pa., U.S.A., September 8–11, 1971.     

The structure of blue supergiant winds and the accretion in supergiant high-mass X-ray binaries

We have developed a stellar wind model for OB supergiants to investigate the effects of accretion from a clumpy wind on the luminosity and variability properties of high-mass X-ray binaries. Assuming that the clumps are confined by ram pressure of the ambient gas and exploring different distributions for their mass and radii, we computed the expected X-ray light curves in the framework of the Bondi–Hoyle accretion theory, modified to take into account the presence of clumps. The resulting variability properties are found to depend not only on the assumed orbital parameters but also on the wind characteristics. We have then applied this model to reproduce the X-ray light curves of three representative high-mass X-ray binaries: two persistent supergiant systems (Vela X−1 and 4U 1700−377) and the supergiant fast X-ray transient IGR J11215−5952. The model can reproduce the observed light curves well, but requiring in all cases an overall mass loss from the supergiant about a factor of 3–10 smaller than the values inferred from ultraviolet lines studies that assume a homogeneous wind.     

Light curve synthesis for binary systems: The stellar wind effect

Synthesis methods for light and radial velocity curves allow one to find the physical parameters of the components of binary systems of different types. We describe the basics of a new light curve synthesis algorithm for binaries that contain stars with extended expanding atmospheres. The algorithm can be used to study, e.g., light curves of binaries that contain Wolf-Rayet stars.