Light curve solutions of six eclipsing binaries at the lower limit of periods for W UMa stars

Photometric observations are presented in V and I bands of six eclipsing binaries at the lower limit of the orbital periods for W UMa stars. Three of them are newly discovered eclipsing systems. The light curve solutions reveal that all shortperiod targets are contact or overcontact binaries and six new binaries are added to the family of short-period systems with estimated parameters. Four binaries have components that are equal in size and a mass ratio near 1. The phase variability shown by the V-I colors of all targets may be explained by lower temperatures on their back surfaces than those on their side surfaces. Five systems exhibit the O'Connell effect that can be modeled by cool spots on the side surfaces of their primary components.The light curves of V1067 Her in 2011 and 2012 are fitted by diametrically opposite spots. Applying the criteria for subdivision of W UMa stars to our targets leads to ambiguous results.     

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.     

First photometric analyses of five contact ASAS binaries

We present the first light curve solutions of five binary systems selected from All Sky Automated Survey (ASAS) Catalog of Variable Stars. The light curves of the systems are analyzed and the light parameters are derived. The estimated absolute parameters of the components and the degree of contact values for all targets are also calculated. We compared our results to other known contact binaries by emphasizing the locations of the components on the mass–radius and the H–R diagram. The evolutionary statuses of the systems are also discussed. Results of our analyses confirm that the systems are contact binaries.     

Photometric light curve solutions of three ultra-short period eclipsing binaries

We present the results of our study of the eclipsing binary systems CSS J112237.1+395219,LINEAR 1286561 and LINEAR 2602707 based on new CCD B, V, Rcand Iccomplete light curves. The ultra-short period nature of these stars, as reported by Drake et al., is confirmed and the system's periods are revised. The light curves were modeled using the 2003 version of the Wilson-Devinney code. When necessary, cool spots on the surface of the primary component were introduced to account for asymmetries in the light curves. As a result, we found that CSS J112237.1+395219 is a W UMa type contact binary system belonging to W subclass with a mass ratio of q = 1.61 and a shallow degree of contact of 14.8%where the primary component is hotter than the secondary one by 500 K. LINEAR 1286561 and LINEAR2602707 are detached binary systems with mass ratios q = 3.467 and q = 0.987 respectively. These detached systems are low-mass M-type eclipsing binaries with similar temperatures. The marginal contact,fill-out factor and temperature difference between components of CSS J112237.1+395219 suggest that this system may be at a key evolutionary state predicted by thermal relaxation oscillation(TRO) theory. From the estimated absolute parameters, we conclude that our systems share common properties with other ultrashort period binaries.     

Updated catalogue of the light curve solutions of contact binary stars

The catalogue of the light curve solutions of contact binary stars was updated. Based on the catalogue data we call the attention to a remarkable gap in the temperature distribution of contact binaries which remained unexplained. The absolute dimensions of the components were calculated in a reliable way. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Photometric solutions of some contact ASAS binaries

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.     

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)     

BV Dra and BW Dra: Two contact systems in one visual binary

UBV light curves obtained in 1975 for both components of ADS 9537 are presented. These light curves and the light curve of BV Dra by Yamasaki have been solved for geometrical parameters using the synthesis method under two hypotheses explaining theW-subclass light curves: (1) temperature excess of the less massive components; (2) spots on the more massive components; the results are very similar. Because of the poor determinacy of the solutions, mass-ratios have been assumed:q=0.8 for BV Dra and a range inq for BW Dra; our solutions suggest preference for smallerq in the latter system. We compare both variables and conclude that they follow the Main Sequence dependences. We give also a bried discussion of the existing information on other contact binaries in multiple (visual) systems: the contact binaries seem to follow the same statistical distributions for occurrence in multiples as found for detached binaries but severe selection effects limit detectability for multiple systems with wide orbits having semi-axes below 100 a.u.On leave from the Warsaw University Observatory.Visiting Astronomer, Kitt Peak National Observatory which is operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation.     

Distributions of Geometrical and Physical Parameters of Contact Binaries

The distributions of geometrical and physical parameters from the CCBS (Catalogue of Contact Binary Stars) and the ASAS-3 (The All Sky Automated Survey) are discussed. The distributions of orbital periods of light curves for 374 contact binaries from the CCBS as well as 3590 contact binaries, selected by Fourier decomposition of 4216 eclipsing binaries from the ASAS-3 database, are similar. The maxima of the period distributions are between 0.31–0.40 days (0.25–0.32 days for W-type and 0.35–0.40 days for A-type) and 0.40–0.45 days for the CCBS and ASAS-3 dataset, respectively.     

Photometric study of five kepler contact binaries

A lot of data in time domain were obtained by the Kepler mission, including many contact binaries. Long-term observation lets us obtain more information about the short time scale variation in their light curves or in their orbital periods. Unfortunately, the exposure time is too long (most of them are 30 minutes). Hence, many variations in light curves are smoothed. To avoid this problem, we analyzed some Kepler contact systems with both long-cadence mode and short-cadence mode data. Using the latest version of the Wilson-Devinney code, we obtained the physical parameters of a batch of contact binaries and find out four targets(KIC 5123176, KIC 5296877, KIC 8496820, KIC 9776718) have low mass ratios (q  <  0.25) and one target (KIC 7950962) has a mass ratio very close to unit.     

Hydromagnetic stability of a gas-liquid interface of coaxial cylinders

The method of Fourier analysis of the light changes in the frequency-domain has been studied and discussed for 92 light curves of different types of eclipsing binary systems.Geometrical and physical elements of the systems under analysis have been listed and discussed, accordingly the advantages and disadvantages of the method is presented.The results show that the method is suitable for analysis of detached and most of the semi-detached systems, while for contact binaries and -Lyrae-type stars it has some difficulties. The light curve synthesis method is recommended.     

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.     

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)     

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.     

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.     

Light curve solutions of the eccentric Kepler binaries KIC 4281895 and KIC 5115178 with tidally-induced humps

The paper presents our light curve solutions of the Kepler data of two eccentric, eclipsing binaries: KIC 4281895 and KIC 5115178. The derived orbital and stellar parameters reveal that their components are of G spectral type and undergo partial eclipses. We found tidally-induced light humps around the periastron phases of the two targets which are appearances of the recently discovered “heartbeat” phenomenon.     

Light curve solutions of the eclipsing Kepler binaries KIC 5080652, KIC 5285607, KIC 9236858 and KIC 11975363

We carried out light curve solutions of four detached binaries with circular orbits, observed by Kepler. As a result their orbital inclinations, temperatures and relative stellar radii were determined. We estimated also their global parameters on the base of the obtained solutions and empirical relation “temperature, luminosity” for MS stars. The out-of-eclipse light curves of KIC 5080652, KIC 9236858 and KIC 11975363 reveal a trend the bigger amplitudes to correspond to single-waved shape while the two-waved shape to be inherent to the smaller amplitudes. This type of variability was attributed to gradually transition between state with two almost opposite cool spots and state with bigger in size polar spot. We detected also several microflares of KIC 11975363 with amplitudes of 0.002–0.003 mag.     

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.     

New Techniques and Limitations of Light Curve Analysis

The solution of light curves of eclipsing binaries provides the simplest way of measuring the basic physical parameters of stars. The development of computers and numerical methods enables us to perform an analysis of large amount of photometric data by comparing it to more and more sophisticated physical models which are also suitable for stellar systems with different peculiarities. Nevertheless, some parameters of stellar systems are poorly determined by light curves alone, and simultaneous fitting together with other data is preferable. The progress of instrumentation not only improves the precision and resolution of data, but also overcomes the classical gaps between stellar systems observable as visual, photometric and spectroscopic binaries. This opens new problems in the development of techniques of data analysis, which can be treated as a generalization of light curve modeling. Some of these directions are outlined here. In particular, the disentangling of spectra with line-profile variability due to proximity effects is discussed.     

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.