Eclipsing Binaries with Possible Light-Time Effect

The period changes of six eclipsing binaries have been studied with focus on the light-time effect. With the least squares method we also calculated parameters of such an effect and properties of the unresolved body in these systems. With these results we discussed the probability of presence of such bodies in the systems with respect to possible confirmation by another method. In two systems we also suggested the hypothesis of fourth body or magnetic activity for explanation of the "second-order variability" after subtraction of the light-time effect of the third body.     

Monitoring Possible Light-Time Effect in the Orbital Period of Some Eclipsing Binaries at the Ankara University Observatory

A significant number of close binaries are known to be members of physically bound triple or multiple star systems. The O – C analysis technique which is based on the minima times of an eclipsing binary can reveal the light-time effect due to the presence of gravitationally bound and generally unseen close component(s) in the system. In this study we present shortly the O – C analysis results based on the light-time effect possibilities for two of the eclipsing binaries observationally followed by our group; TZ Boo and CF Tau.     

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.     

Disentangling Effective Temperatures of Individual Eclipsing Binary Components by Means of Color-Index Constraining

Eclipsing binary stars are gratifying objects because of their unique geometrical properties upon which all important physical parameters such as masses, radii, temperatures, luminosities and distance may be obtained in absolute scale. This poses strict demand on the model to be free of systematic effects that would influence the results later used for calibrations, catalogs and evolution theory. We present an objective scheme of obtaining individual temperatures of both binary system components by means of color-index constraining, with the only requirement that the observational data-set is acquired in a standard photometric system. We show that for a modest case of two similar main-sequence components the erroneous approach of assuming the temperature of the primary star from the color index yields temperatures which are systematically wrong by ∼ 100K.     

Doing Research on Eclipsing Binary Stars with Small Telescopes and PC computers

Astronomical research with a small telescope (20 cm – 40 cm) has always been a challenging problem. The invention of CCD cameras and personal computers has now put this question to past as small telescopes can do good and practicle science. This paper describes the use of small telescope in the study of eclipsing binary stars. Binary stars play an important role as astrophysical laboratories in our quest to understand the evolution and structure of stars. The most useful aspects of research with a small telescope in binary star research is; 1) as a viable teaching laboratory for begining students 2) to teach and learn the fundamental observational techniques that are common to many types of astronomical research areas 3) as a starting point to initiate research programs in observational astronomy, optics, instrumentation, computational astrophysics and 4) as a foundation to develop an infrastructure and technical know how for larger telescope facility. This revised version was published online in July 2006 with corrections to the Cover Date.     

Wind Ionization Structure of the Short-Period Eclipsing LMC Wolf-Rayet Binary BAT99-129: Preliminary Results

BAT99-129 is a rare, short-period eclipsing Wolf-Rayet binary in the Large Magellanic Cloud. We present here medium-resolution NTT/EMMI spectra that allow us to disentangle the spectra of the two components and find the orbital parameters of the binary. We also present VLT/FORS1 spectra of this binary taken during the secondary eclipse, i.e. when the companion star passes in front of the Wolf-Rayet star. With these data we are able to extract, for the first time in absolute units for a WR + O binary, the sizes of the line emitting regions.Based on observations obtained at the La Silla and Paranal Observatories, European Southern Observatory (Chile).     

Light-Time Effect in the Eclipsing Binaries GO Cyg, GW Cep, AR Aur and V505 Sgr

Orbital period changes of the eclipsing binaries GO Cyg and GW Cep are explained by the light-time effect for the first time. New minima of the eclipsing binary AR Aur improve the predicted light-time orbit. The light-time orbit with the quadratic ephemeris of the binary matches the new observations of V505 Sgr better than the linear one. As the light-time effect fits in corresponding O − C diagrams of all four systems have been reaching extreme values, the observations of minima times in forthcoming years are highly desirable.     

Eclipsing Binary Stars in Nearby Galaxies

We briefly discuss the survey programme we are conducting to detect eclipsing binaries in local group galaxies. Some lightcurves from studies of M31, IC 1613 and NGC 6822 are presented along with details of future work.     

Monitoring Secular Orbital Period Variations of Some Eclipsing Binaries at the Ankara University Observatory

This study concerns the long-term monitoring of the secular variation character in the orbital period of some short-period eclipsing binaries observed at the Ankara University Observatory. Among the systems of our observing list are CK Boo, V502 Oph and V836 Cyg that show long-term secular variations in their orbital periods. We use classical O-C diagram analysis technique as a tool to reveal the character of the period variations of these binary systems.     

EPIC 202060577的双星解轨和物理参数研究

EPIC 202060577是一个包含B型子星的食双星系统.根据K2测光数据获得了45个次极小时刻,确定其轨道周期为1.019648 d并给出了历元公式.基于大天区面积多目标光纤光谱望远镜(Large Sky Area Multi-Object Fiber Spectroscopic Telescope, LAMOST1,又称郭守敬望远镜)的光谱数据,使用ROTFIT程序获得了目标系统的主星光谱型、有效温度、金属丰度与表面重力加速度,并计算得到了视向速度曲线.通过PHOEBE (Physics Of Eclipsing Binaries)建模程序和emcee (Affine Invariant Markov chain Monte Carlo Ensemble Sampler)拟合程序,对EPIC 202060577进行了轨道求解并分析了RossiterMcLaughlin效应对视向速度曲线的影响.最终结果表明EPIC 202060577是一个质量比q=0.11的分离结构食双星系统(q=M2/M1, M1、M2分别为主星和伴星质量),主星的光谱型为B2/3,主星和伴星的质量、半径和有效温度分别为M1=12.56M⊙和M2=1.39M⊙,R1=4.58Rsun和R2=1.85Rsun, T1=18979 K和T2=8710 K, M⊙和Rsun分别为太阳质量和半径.根据所获得的物理参数,对EPIC 202060577的演化阶段进行了讨论.     

A Library of Eclipsing Binary Light-Curves: Fast Initial Parameters Estimation, and on the Uniqueness of the Inverse Problem

In order to improve the light curve solutions we suggest to use a new approach. A library of the Fourier-coefficients (up to 20th term) of (several millions of) light curves was constructed each of the light curves has different input parameters. A light curve solution is made in a very fast way: its discrete Fourier-transform yields not more than some simple number which are compared to the Fourier-coefficients in the library. A chi-squared test can help us to estimate very good initial parameters for the differential correction analysis. The library can also be used to study the uniqeness problem of the light curve solutions. Here we investigated the uniqueness of the spot solution of SV Cam.     

HD 172189, a Cluster Member Binary System with a δ Scuti Component in the Field of View of COROT

Photometric and spectroscopic results for the star HD 172189, member of the open cluster IC 4756 in the summer field of the space mission COROT, are presented. From photometric observations in the Strömgren system carried out at various epochs, its binary nature as well as the presence of a δ Scuti-type pulsating component have been discovered. The frequency analysis of the whole dataset confirms a dominant frequency of 19.5974 c d^?1 with a maximum amplitude near 0.02 mag plus other frequencies in the range 18–20 c d^?1. A preliminary orbital solution from the light curve and from four FEROS spectra reveals two similar components of around 1.5 M _⊙ orbiting with a period of 5.702 d.     

A Method For Eclipsing Component Identification in Large Photometric Datasets

We describe an automated method for assigning the most likely physical parameters to the components of an eclipsing binary (EB), using only its photometric light curve and combined color. In traditional methods (e.g. WD and EBOP) one attempts to optimize a multi-parameter model over many iterations, so as to minimize the chi-squared value. We suggest an alternative method, where one selects pairs of coeval stars from a set of theoretical stellar models, and compares their simulated light curves and combined colors with the observations. This approach greatly reduces the EB parameter-space over which one needs to search, and allows one to determine the components' masses, radii and absolute magnitudes, without spectroscopic data. We have implemented this method in an automated program using published theoretical isochrones and limb-darkening coefficients. Since it is easy to automate, this method lends itself to systematic analyses of datasets consisting of photometric time series of large numbers of stars, such as those produced by OGLE, MACHO, TrES, HAT, and many others surveys.     

On using the beaming effect to measure spin-orbit alignment in stellar binaries with Sun-like components

The beaming effect (aka Doppler boosting) induces a variation in the observed flux of a luminous object, following its observed radial velocity variation. We describe a photometric signal induced by the beaming effect during eclipse of binary systems, where the stellar components are late type Sun-like stars. The shape of this signal is sensitive to the angle between the eclipsed star’s spin axis and the orbital angular momentum axis, thereby allowing its measurement. We show that during eclipse there are in fact two effects, superimposed on the known eclipse light curve. One effect is produced by the rotation of the eclipsed star, and is the photometric analog of the spectroscopic Rossiter-McLaughlin effect, thereby it contains information about the sky-projected spin-orbit angle. The other effect is produced by the varying weighted difference, during eclipse, between the beaming signals of the two stars. We give approximated analytic expressions for the amplitudes of the two effects, and present a numerical simulation where we show the light curves for the two effects for various orbital orientations, for a low mass ratio stellar eclipsing binary system. We show that although the overall signal is small, it can be detected in the primary eclipse when using Kepler Long Cadence data of bright systems accumulated over the mission lifetime.     

Radial Velocity and Light Curves Analysis of the Contact Binary V1073 Cygni

In this study complete BV light curves of the W Ursae Majoris binary V1073 Cygni obtained in 2005 are presented. We have used the spectroscopic data of V1073 Cyg obtained by Ahn et al. (1992) for analysis. The analysis of radial velocity and light curves was made with Wilson} program (1998) and the geometric and physical elements} of the system were derived. By searching the simultaneous} solutions of the system, we have determined the masses and radii of the components: 1.64M_⊙, 2.275R_⊙ for the primary component and 0.55M_⊙, 1.397R_⊙ for the secondary component respectively. The effective temperature of 6494 ± 53 K for the secondary component was also estimated.     

Modeling the 2004.5 Brightening of the Contact Binary V839 Oph

Time-series CCD photometry of the contact system V839 Oph on May, June and July 2004 showed a continuous brightening of the system in all phases of the light curve. A possible explanation of this brightening could be enhanced (magnetic) activity of the system, also noticed in the past. Mass transfer and/or energy exchange between the two components can explain the observed increase of brightness. All possible cases, concerning the location and shape of the spotted area, are discussed and the most probable model is presented.     

Photometric and spectroscopic investigation of the oscillating Algol type binary: EW Boo

We obtained the physical and geometrical parameters of the EW Boo system, which exhibits short period and small amplitude pulsations as well as brightness variations due to orbital motion of components. Towards this end we carried out photometric observations at Ankara University Kreiken Observatory (AUKO) as well as spectroscopic observations at TUBITAK National Observatory (TNO). The light and radial velocity curves obtained from these observations have been simultaneously analyzed with PHOEBE and the absolute parameters of the system along with the geometric parameters of the components have been determined. Using model light curves of EW Boo, light curve regions in which the pulsations are active have been determined and as a result of analyses performed in the frequency region, characteristic parameters of pulsations have been obtained. We find that the results are compatible with current parameters of similar systems in the literature. The evolutionary status of the components is propounded and discussed.