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.     

Eclipsing Binaries in Open Clusters

The study of detached eclipsing binaries in open clusters can provide stringent tests of theoretical stellar evolutionary models, which must simultaneously fit the masses, radii, and luminosities of the eclipsing stars and the radiative properties of every other star in the cluster. We review recent progress in such studies and discuss two unusually interesting objects currently under analysis. GV Carinae is an A0 m + A8 m binary in the Southern open cluster NGC 3532; its eclipse depths have changed by 0.1 mag between 1990 and 2001, suggesting that its orbit is being perturbed by a relatively close third body. DW Carinae is a high-mass unevolved B1 V + B1 V binary in the very young open cluster Collinder 228, and displays double-peaked emission in the centre of the Hα line which is characteristic of Be stars. We conclude by pointing out that the great promise of eclipsing binaries in open clusters can only be satisfied when both the binaries and their parent clusters are well-observed, a situation which is less common than we would like.     

Eclipsing binaries in the All Sky Automated Survey catalogue

The All Sky Automated Survey (ASAS) is a long-term project to monitor bright variable stars over the whole sky. It has discovered 50 099 variables brighter than   V < 14 mag  south of declination +28°, and among them 11 076 eclipsing binaries. We present a preliminary analysis of 5384 contact, 2949 semi-detached, and 2743 detached systems. The statistics of the distribution provides a qualitative confirmation of decades old idea of Flannery and Lucy that the W UMa-type binaries evolve through a series of relaxation oscillations: the ASAS finds comparable number of contact and semi-detached systems.
The most surprising result is a very small number of detached eclipsing binaries with periods   P < 1 d  , the systems believed to be the progenitors of the W UMa stars. As many (perhaps all) contact binaries have companions, there is a possibility that some were formed in a Kozai cycle, as suggested by Eggleton and his associates.     

The first light-curve analysis of eclipsing binaries observed by the INTEGRAL/OMC

Three Algol-type binaries in Cygnus constellation were selected for an analysis from a huge database of observations made by the INTEGRAL/OMC camera. These data were processed and analyzed, resulting in a first light-curve study of these neglected eclipsing binaries. The temperatures of the primary components range from 9500 K to 10,500 K and the inclinations are circa 73° (for PV Cyg and V1011 Cyg), while almost 90° for V822 Cyg. All of them seem to be main-sequence stars, well within their critical Roche lobes. Nevertheless, further detailed analyses are still needed.     

A search for wide visual companions of exoplanet host stars: The Calar Alto Survey

We have carried out a search for co‐moving stellar and substellar companions around 18 exoplanet host stars with the infrared camera MAGIC at the 2.2 m Calar Alto telescope, by comparing our images with images from the all sky surveys 2MASS, POSS I and II. Four stars of the sample namely HD80606, 55 Cnc, HD46375 and BD–10°3166, are listed as binaries in the Washington Visual Double Star Catalogue (WDS). The binary nature of HD80606, 55 Cnc, and HD46375 is confirmed with both astrometry as well as photometry, thereby the proper motion of the companion of HD46375 was determined here for the first time.We derived the companion masses as well as the longterm stability regions for additional companions in these three binary systems. We can rule out further stellar companions around all stars in the sample with projected separations between 270AU and 2500AU, being sensitive to substellar companions with masses down to ∼60 M_Jup (S /N = 3). Furthermore we present evidence that the two components of the WDS binary BD–10°3166 are unrelated stars, i.e this system is a visual pair. The spectrophotometric distance of the primary (a K0 dwarf) is ∼67 pc, whereas the presumable secondary BD–10°3166B (a M4 to M5 dwarf) is located at a distance of 13 pc in the foreground. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Light-curve analysis and eclipse mapping of the contact binaries KQ Gem and V412 Her

CCD photometry of the short-period binary stars KQ Gem and V412 Her is presented, together with some spectroscopic observations of KQ Gem. Although both systems are classified in the General Catalogue of Variable Stars as having light curves of EB/KW type, our data and analyses, involving light-curve synthesis and stellar surface imaging, show that KQ Gem is an EB system that is in marginal contact and has an enhanced bright region around the substellar point on the secondary component, whilst V412 Her is an EW system, a true contact binary with a mass ratio of 0.46 and both stars having the same surface brightness. The properties of the components of the two systems are compared with other marginal-contact and contact binaries, and a plea is repeated for more theoretical work on the mass/energy interchanges in contact binaries.     

The CCD photometric study of the newly identified RS CVn binary star V1034 Hercules

This paper presents a new CCD Bessell VR_cI_c light curves and photometric analysis of the newly discovered RS CVn type eclipsing binary star V1034 Her. The light curves were obtained at the Çanakkale Onsekiz Mart University Observatory in 2006. Variations of the orbital period of the system were firstly studied. The (O − C) diagram with a low range of observing time of about 20 years shows an upward parabola, which indicates a secular increase in the orbital period of the system. The light curves are generally those of detached eclipsing binaries; however, there are large asymmetries between maxima. The VR_cI_c light curves were analysed with two different fitting procedures: Wilson–Devinney method supplemented with a Monte Carlo type algorithm and Information Limit Optimization Technique (ILOT). Our general results find V1034 Her. as a well detached system, in which the components are filling 65% of their Roche lobes. Light curve asymmetries of the system are explained in terms of large dark starspots on the primary component. The primary star shows a long-lived spot distribution with active longitudes in the same hemisphere.     

Velocity curve analysis of the spectroscopic binary stars PV Pup,HD 141929, EE Cet and V921 Her by nonlinear regression

We use the method introduced by Karami & Mohebi (2007), and Karami & Teimoorinia (2007) which enable us to derive the orbital parameters of the spectroscopic binary stars by the nonlinear least squares of observed vs. curve fitting (o-c). Using the measured experimental data for radial velocities of the four double-lined spectroscopic binary systems PV Pup, HD 141929, EE Cet and V921 Her, we find both the orbital and the combined spectroscopic elements of these systems. Our numerical results are in good agreement with those obtained using the method of Lehmann-Filhés.     

Sixty four nights of UBV photometry of early‐type stars at La Sila

UBV measurements of early‐type stars, mostly eclipsing binaries, obtained at La Silla in the years 1990 to 1994 with the ESO 50 cm telescope are presented. Most of these data were already used in our individual studies of several binaries. Now all photometric measurements were reduced again with an advanced technique and are made available electronically. Our data for MY Ser have not yet been published; new light curve is given and solved. The result is that MY Ser is a contact binary, with very large fill‐out parameter. Also a light curve and its solution for V1051 Cen are provided, and the problem of the period of V871 Cen is pointed out. Besides binaries (and the comparison and check stars) data for several stars in southern H II regions are included. Extinction and transformation coefficients are given (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

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.     

Eclipsing binaries in the MOST satellite fields

Sixteen new eclipsing binaries have been discovered by the MOST satellite among guide stars used to point its telescope in various fields. Several previously known eclipsing binaries were also observed by MOST with unprecedented quality. Among the objects we discuss in more detail are short‐period eclipsing binaries with eccentric orbits in young open clusters: V578 Mon in NGC 2244 and HD 47934 in NGC 2264. Long nearly‐continuous photometric runs made it possible to discover three long‐period eclipsing binaries with orbits seen almost edge‐on: HD 45972 with P = 28.1 days and two systems (GSC 154 1247 and GSC 2141 526) with P > 25 days. The high precision of the satellite data led to discoveries of binaries with very shallow eclipses (e.g., HD 46180 with A = 0.016 mag, and HD 47934 with A = 0.025 mag). Ground‐based spectroscopy to support the space‐based photometry was used to refine the models of several of the systems (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Accretion and dynamical interactions in small-N star-forming clusters: N= 5

We present results from high-resolution hydrodynamical simulations that explore the effects of small-scale clustering in star-forming regions. A large ensemble of small- N clusters with five stellar seeds have been modelled and the resulting properties of stars and brown dwarfs statistically derived and compared with observational data.
Close dynamical interactions between the protostars and competitive accretion driven by the cloud collapse are shown to produce a distribution of final masses that is bimodal, with most of the mass residing in the binary components. When convolved with a suitable core mass function, the final distribution of masses resembles the observed initial mass function, in both the stellar and substellar regimes. Binaries and single stars are found to constitute two kinematically distinct populations, with about half of the singles attaining velocities ≥2 km s⁻¹, which might deprive low-mass star-forming regions of their lightest members in a few crossing times. The eccentricity distribution of binaries and multiples is found to follow a distribution similar to that of observed long-period (uncircularized) binaries.
The results obtained support a mechanism in which a significant fraction of brown dwarfs form under similar circumstances as those of normal stars but are ejected from the common envelope of unstable multiple systems before their masses exceed the hydrogen burning limit. We predict that many close binary stars should have wide brown dwarf companions. Brown dwarfs, and, in general, very low-mass stars, would be rare as pure binary companions. The binary fraction should be a decreasing function of primary mass, with low-mass or substellar primaries being scarce. Where such binaries exist, they are expected either to be close enough (semimajor axis ∼10 au) to survive strong interactions with more massive binaries or to be born in very small molecular cloud cores.     

The proper-motion signal of unresolved binaries in the Hipparcos catalogue

We present an investigation of the differences between quasi-instantaneous stellar proper motions from the Hipparcos catalogue and long-term proper motions determined by combining Hipparcos and the Astrographic Catalogue. Our study is based on a sample of about 12000 stars of visual magnitude from 7 to 10 in two declination zones on the northern and equatorial sky. The distribution of the proper-motion differences shows an excess of large deviations. This is caused by the influence of orbital motion of unresolved binary systems. The proper-motion deviations provide statistical evidence for 360 astrometric binaries in the investigated zones, corresponding to about 2400 such binaries in the entire Hipparcos catalogue, in addition to those already known. In order to check whether the observed deviations are compatible with standard assumptions on the basic parameters of binary stars, we model the impact of orbital motion on the observed proper motions in a Monte Carlo simulation. We show that the simulation yields an acceptable approximation of the observations, if a binary frequency between 70% and 100% is assumed, i.e.if most of the stars in the sample are assumed to have a companion. Thus Hipparcos astrometric binaries confirm that the frequency of non-single stars among field stars is very high. We also investigate the influence of the mass function for the secondary component on the result of the simulation. A constant mass function and mass functions with moderate increase towards low masses lead to results, which are compatible with the observed proper-motion effects. A high preponderance of very-low-mass or substellar companions as produced, for example, by a M^—1 power law is not in agreement with the frequency of proper-motion deviations in our sample of stars.     

First analysis of eight Algol-type systems: V537 And,GS Boo,AM CrB,V1298 Her,EL Lyn,FW Per,RU Tri,and WW Tri

Analyzing available photometry from the Super WASP and other databases, we performed the very first light curve analysis of eight eclipsing binary systems V537 And, GS Boo, AM CrB, V1298 Her, EL Lyn, FW Per, RU Tri, and WW Tri. All of these systems were found to be detached ones of Algol-type, having the orbital periods of the order of days. 722 new times of minima for these binaries were derived and presented, trying to identify the period variations caused by the third bodies in these systems.     

A Possible Explanation of the O‘Connell Effect in Close Binary Stars

A theoretical model for explaining the O‘Connell effect of close binary stars is given based on the hypothesis that the circumstellar material of a binary system is captured by its components.The results inferred form the model suggest that late-type and /or short-period binaries can easily produce obvious O‘Connell effect and that the occurrence of O‘Connell effect has no relation with the type of binaries,These conclusions are in agreement with the observed results.The observed O‘Connell effects of six binary systems are examined by the model.For three W-subtype W UMa binaries(YY Eri,BX Per and SW Lac).the densities of the materials captured by the two components are assumed to be equal,and the calculated O‘Connell effect is found to be almost equal to the observed effect.For three A-subtype W UMa systems(CN And,FG Hya and AU Ser),the two densities are assumed to be different,and are calculated separately.The calculated O‘Connell effect turns out to agree better with the observed effect than that was formerly obtained.     

Are the W Ursae Majoris-type systems EK Comae Berenices and UX Eridani surrounded by circumstellar matter?

The variations of the orbital periods of two nearly neglected W UMa-type eclipsing binaries, EK Comae Berenices and UX Eridani, are presented through a detailed analysis of the O–C diagrams. It is found that the orbital period of EK Com is decreasing and the period of UX Eridani is increasing, and several sudden jumps have occurred in the orbital periods of both binaries. We analyze the mechanism(s), which might underlie the changes of the orbital periods of both systems, and obtain some new results. The long-term decrease of the orbital period of EK Comae Berenices might be caused by the decrease of the orbital angular momentum due to a magnetic stellar wind (MSW) or by mass transfer from the more massive to the less massive component. The secular increase in the orbital period of UX Eridani might be caused by mass transfer from the less massive to the more massive star. The possible mechanisms, which underlie the sudden changes in the orbital periods of the close binary systems are as the followings: (1) the variations of the structure due to the variation of the magnetic field; (2) the rapid mass exchange between the close binaries and their circumstellar matter. Finally, the evolutionary status of the systems EK Comae Berenices and UX Eridani is discussed.     

Abundances from Disentangled Component Spectra of Close Binary Stars: An Observational Test of an Early Mixing in High-Mass Stars

Recent theoretical calculations of stellar evolutionary tracks for rotating high-mass stars suggests that the chemical composition of the surface layers changes even whilst the star is evolving on the Main Sequence. The abundance analysis of binary components with precisely known fundamental stellar quantities allows a powerful comparison with theory. The observed spectra of close binary stars can be separated into the individual spectra of the component stars using the method of spectral disentangling on a time-series of spectra taken over the orbital cycle. Recently, Pavlovski and Hensberge (2005, A&A, 439, 309) have shown that, even with moderately high line-broadening, metal abundances can be derived from disentangled spectra with a precision of 0.1 dex. In a continuation of this project we have undertaken a detailed abundance analysis of the components of another two high-mass binaries, V453 Cyg, and V380 Cyg. Both binaries are well-studied systems with modern solutions. The components are close to the TAMS and therefore very suitable for an observational test of early mixing in high-mass stars.     

Hα Photometry of Two Contact Binaries

We carried out optical and Hα photometry of two contact binaries (V861 Herculis, EQ Tauri). The light curve modeling revealed stellar spots in both contact systems and strong Hα excess in the position of the observed stellar spots. A correlation was found between the V−R and R−H_α colour indices of V861 Her.     

Velocity curve analysis of the spectroscopic binary stars RZ Cas,CC Cas,HS Her,HD 93917, V921 Her and Y Cygni by the artificial neural networks

We use an Artificial Neural Network (ANN) to derive the orbital parameters ofspectroscopic binary stars. Using measured radial velocity data of six double‐lined spectroscopic binary systems RZ Cas, CC Cas, HS Her, HD 93917, V921 Her and Y Cygni, we find corresponding orbital and spectroscopic elements. Our numerical results are in good agreement with those obtained by others using more traditional methods (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Light curve solutions of the ultrashort‐period Kepler binaries

We carried out light‐curve solutions of the ultrashort‐period binaries with MS components observed by Kepler. All six targets turned out almost in thermal contact with contact or slightly overcontact configurations. Two of them, KID 4921906 and KID 6309193, are not eclipsing but reveal ellipsoidal and spot variability. One of the components of KID 8108785 exhibits inherent, quasi‐sinusoidal, small‐amplitude variability. KID 12055255 turned out tobe a very rare case of ultrashort‐period overcontact binary consisting of two M dwarfs. Our modeling indicated that the variability of KID 9532219 is due to eclipses but not to δ Sct pulsations as it was previously supposed. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)