The very short period W UMa system V 1022 Ophiuchi

Photoelectric light curves of V1022 Oph inB andV are presented. It has been confirmed that it is a W UMa type eclipsing binary with one of the shortest periods known (P<0.^d25). Some general properties of the system have been derived.Based on observations made at the European Southern Observatory (La Silla/Chile)     

Photometric Elements of the Eclipsing Binary AZ Vir

Using WOOD 's (1972) model we have analyzed MEINUNGER 's (1977) B and V photoelectric light curves – as yet unsolved–of the W UMa-type eclipsing binary AZ Vir, for which no photometric elements have as yet been determined. Our results describe AZ Vir as a contact pair in which the star eclipsed at the deeper minimum is smaller than its companion. AZ Vir appears to conform to the general properties of the W-type subclass of W UMa systems.     

Contact Binaries: A Study of the Proximity Effects and Gravity Darkening Based on Kopal’s Fourier Method

A new method for the determination of the proximity effects and gravity darkening exponents in contact binaries of W UMa type is presented. The method is based on Kopal’s method of Fourier analysis of the light changes of eclipsing variables in the Frequency Domain. The method was applied to 36 W UMa systems for which geometric and photometric elements have been derived by the most powerful techniques. The derived values are very close to those predicted by the existing theory of radiative transfer or convective equilibrium.     

New absolute magnitude calibrations for WUrsa Majoris type binaries

Parallaxes of W UMa stars in the Hipparcos catalogue have been analyzed. 31 W UMa stars, which have the most accurate parallaxes (σ_π /π < 0.15) which are neither associated with a photometric tertiary nor with evidence of a visual companion, were selected for re‐calibrating the Period‐Luminosity‐Color (PLC) relation of W UMa stars. Using the Lutz‐Kelker (LK) bias corrected (most probable) parallaxes, periods (0.26 < P < 0.87, P in days), and colors (0.04 < (B – V)₀ < 1.28) of the 31 selected W UMa, the PLC relation have been revised and re‐calibrated. The difference between the old (revised but not bias corrected) and the new (LK bias corrected) relations are almost negligible in predicting the distances of W UMa stars up to about 100 pc. But, it increases and may become intolerable as distances of stars increase. Additionally, using (J – H)₀ and (H – K_s)₀ colors from 2MASS (TwoMicron All Sky Survey) data, a PLC relation working with infrared data was derived. It can be used with infrared colors in the range –0.01 < (J – H)₀ < 0.58, and –0.10 < (H – K_s)₀ < 0.18. Despite of the fact that the 2MASS data refer to single epoch observations which are not guaranteed to be taken at maximum brightness of theWUMa stars, the established relation has been found surprisingly consistent and reliable in predicting LK corrected distances of W UMa stars (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

X-ray emission from the W UMa system TZ Bootis

HEAO-B (Einstein) satellite measurements with the Imaging Proportional Counter revealed the W UMa binary system TZ Bootis as an X-ray source. It is estimated that the luminosity ratioL _x/L_vof this system is about 10^–3.8 indicating that TZ Bootis is in the transition region between A- and W-type W UMa systems.     

A photometric study of V566 ophiuchi

The A-type W UMa system V566 Oph was observed photoelectrically in two wavebands (B andV) in the years 1988-1989 at the Kryonerion Astronomical Station of the National Observatory of Athens, Greece. The light curves of the system are analyzed using frequency-domain techniques and new geometric and photometric elements are derived. These elements are combined with the more recent spectroscopic data based on Reticon observations to yield the absolute parameters of the system. The evolutionary status of the system is considered and it is found that V566 Oph has started its evolution away from the Main Sequence. The period of the system continues to increase.     

V758 Centauri:UBV photometry

The W UMa system V758 Centauri has been observed photoelectrically in theUBV system at Bosque Alegre Station, and the comparison and check stars at Cerro Tololo Observatory. Full light curves were constructed from 1043 differentialUBV observations. A study of 11 photoelectric times of minimum light and of earlier photographic data shows that the period remained constant in the last century, V758 Cen shows a total occultation at secondary minimum, thus being an A-type W UMa system. Asymmetries are observed at primary minima whereas maxima are of different heights. Thermal decoupling of the components is suggested by the depth ratio of the minima; V758 Cen may be at the broken phase (or marginal contact) of a thermal relaxation oscillation.     

Seven years photometry of the W UMa‐type eclipsing binary V2612 Oph

We present the first long‐term Johnson UBVR observations and comprehensive photometric analysis of the W UMa‐type eclipsing binary V2612 Oph. Observations in the time interval between 2003 and 2009 enabled us to reveal the seasonal and long‐term variations of the light curve. Hence, we found that the mean brightness level of the light curve shows a variation with a period of 6.7 years. Maximum and minimum brightness levels of the light curve exhibit a variation from year to year which we attribute to a solar‐like activity. The O – C variation of eclipse timings of the system shows a decreasing parabolic trend and reveals a period decrease at a rate of P = 6.27×10^‐7 day yr^‐1 with an additional low‐amplitude sinusoidal variation that has a similar period as the long‐term brightness variations. Our light curve analysis shows that the system is a W‐subtype W UMa eclipsing binary. We calculated masses and radii of the primary and secondary components as M₁ = 1.28 M_⊙, M₂ = 0.37 M_⊙ and R₁ = 1.31 R_⊙, R₂ = 0.75 R_⊙, respectively. The derived absolute photometric parameters allow us to calculate a distance of 140 pc, which confirms that the system is a foreground star in the sky field of the Galactic open cluster NGC 6633. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Photometric solution for the eclipsing binary system AO Camelopardalis

UBV light curves of AO Cam were analyzed with Wilson and Devinney's model. The system was found to be a contact configuration with a degree of overcontact of 1.4%. The mass ratio of the system is about 1.30, and the inclination is 75 _. ⁰ 9. The primary eclipse appears to be an occultation. Thus AO Cam has the characteristics of a W-type W UMa system. Its location in a period-spectral type diagram suggests that the system may be a zero-age contact system.     

New CCD photometry of the eclipsing binary system V1067 Her

We present a new set of CCD photometric observations for the short period eclipsing binary 1SWASP J1743 (= V1067 Her). We have determined the available times of light minima and two new linear and quadratic ephemerides have been obtained. The photometric solutions for the system have been performed using Wilson and Devinney Code. The 3D and fill out configuration revealed that V1067 Her is an over contact W UMa binary with relatively low fill-out factor of about 16%.We investigated the period variation for the system. It showed a strong evidence of period changes by using the (O-C) residual diagram method and we have concluded long-term orbital period decrease rate dP/dt= −3.0 × 10⁻⁷ d/yr, corresponding to a time scale 8.6 × 10⁵ yr. Such period decrease in the A-type W UMa systems is usually interpreted to be due to mass transfer from the more to the less massive component.     

1990 photometry of a small amplitude W UMa system LS Delphini

DifferentialUBV observations, carried out in 1990 observing season, of a small amplitude (0 _. ^m 15 inV andB) W UMa system LS Del = HD 199497 are presented. Wavelength-dependent light variations from cycle to cycle indicate that the system is in a very active phase, probably due to magnetic flare activity or mass transfer in the system. An analysis of the minima times indicate a probable secular increase of the photometric period which requires a mass transfer from less massive to more massive component. If this is true then the reverse-algol model by Liuet al. (1988) for this system would not be valid.     

Detection of a coherent oscillation with a 769.63-s period in the intermediate polar EI UMa (PG 0834+488)

Recently, it has been shown that the cataclysmic variable EI UMa should be attributed to intermediate polars on the basis of its X-ray spectrum. However, no short-period oscillations with a high degree of coherence typical of intermediate polars could be detected in this star. Therefore, it was suggested to call it a “hidden” intermediate polar. Using a multichannel photometer and a 70-cm telescope, we performed observations of EI UMa for 60 h. Analysis of the observations has clearly revealed a brightness oscillation with a period of 769.63±0.10 s and a mean semiamplitude of 0_· ^m 008 completely coherent during one month of our observations that was detectable during each of the 13 observing nights. On the basis of this detection, EI UMa should be considered a classical intermediate polar rather than a hidden one. In addition, we have managed to detect the orbital variability of EI UMa for the first time. The orbital light curve is extremely interesting, showing evidence of partial eclipses of the accretion flow.     

Synthetic light curves of two eclipsing binary systems,U Sge and AW UMa

Photometric curve fits have been investigated by means of numerical quadratures to develop theoretical light curves appropriate to stars built up in accordance with the Roche model. The method has been applied previously to β Per (Al-Naimiy and Budding, 1977) on the basis of available observations in red and infrared, while presently applied to two systems with contact components.

1. U Sge, spherical primary totally eclipsed by a contact component secondary. Improved photometric elements of the system have been found, and compared with those obtained by Kopal's method in the frequency domain. The outcome of the curve fitting corresponds well with the results of an analysis in the frequency domain.
2. AW UMa, exhibiting the shallowest minima known for totally eclipsing W UMa systems. The physical and geometrical elements of the system have been found, and the contact nature of the two components confirmed.

     

Ultraviolet light curves of V535 Arae

Observations of V535 Ara obtained with IUE define the light curve of this long-period W UMa binary in the ultraviolet and let us estimate its gravity darkening. This star was chosen as a contact binary near the high-T _eff limit for convection. The ultraviolet colours and spectral type correspond to (B–V)₀=0.24, or A8V, and imply the star should have very little residual convection in its envelope. The gravity darkening thus ought to be large, as in a radiative star, unless it is modified by circulation in the common envelope, or unless all stars this warm are convective. The light-curve analysis is complicated by a long-term wave that depresses the orbital phases before and after secondary eclipse. We have obtained four solutions to a combination of optical and ultraviolet light curves, two for high, radiative gravity darkening and two for low, convective gravity darkening. For each value of the gravity-darkening exponent, we let the larger, more massive binary component either (a) have a dark spot in its back side or (b) have an excessively hot side facing its companion. The light curves were fitted equally well in all four cases; however, in all but the one with low-gravity darkening and a hot inner face there was a rather large global temperature difference between the two stars. The primary component of this system appears to be significantly undermassive for its spectral type, more so than the primary in AW UMa, but this probably results simply from systematic errors in a radial-velocity solution by Schöffel. It is suggested that the W UMa binaries are found only at spectral types later than about A8 because their outer envelopes must be convective to transfer luminosity.     

Photometric analysis of recently discovered eclipsing binary GSC 00008-00901

Photometric analysis of BVR _C light curves of newly discovered eclipsing binary GSC 0008-00901 is presented. The orbital period is improved to 0.28948(11) days. Photometric parameters are determined as well. The analysis yielded to conclusion that system is an over-contact binary of W UMa type with components not in thermal contact. The light curves from 2005 show the presence of a spot on the surface of one of the components, while light curves from 2006 are not affected by maculation.     

Photoelectric study of AW UMa

UBV photoelectric photometry of the eclipsing binary system AW UMa has been presented. A slightly improved period of 0 _. ^d 4387304 has been given. The colour of the system has been discussed. Eccentricity is present in the system. Light and colour curves show that intrinsic light variations may be present in the system. The presence of mass transfer is a possibility.     

Aq Psc – Analysis of New Light Curves

New BV light curves of the A-type W UMa star AQ Psc (P = 0.476d) have been observed and are described. A few times of minimum light are obtained and the ephemeris is improved. The light curves are analyzed for the binary parameters with a light curve synthesis method. Combining the results with Lu and Rucinski’s spectroscopic mass ratio we determined the masses and radii of the components: M ₁ = 1.69M _⊙, M ₂ = 0.38M _⊙, R ₁ = 1.77R _⊙, and R ₂ = 0.89R _⊙.     

Period study of AW UMa

A detailed period study of the eclipsing binary system AW UMa is presented. A new period (P=0^d.4387317) is given. Period changes in different portions of the O-C diagram, based on new period, have been estimated. The total change in period (P) ranges from 2.2×10^–7 to 2.8×10^–6 d, which is normal for AW UMa systems. Two distinct linear trends of period are visible in the O-C diagram. A third trend shows a new change in the period behaviour, which is yet to be confined.     

The peculiar eclipsing star BD+13°3496 (V508 ophiuchi): New BV observations and light curve analysis

New BV photoelectric observations of the W UMa-type system V508 Ophiuchi, made in 1986 at the Kryonerion Astronomical Center of the National Observatory of Athens, Greece, are given. The corresponding mean light curves, as well as those obtained in 1981 at the same station using the same instruments, are analysed using frequency-domain techniques. The geometrical and photometric elements of the system have been found. These are combined with the now available spectroscopic data of the system to get its absolute elements. A general discussion for the light variations between the old and the new observations is made. From the light curve analysis it was found that V508 Oph is an A-type W UMa binary with both of its components to fill their corresponding Roche lobes.     

食双星的分光轨道解:AA UMa

使用像管摄谱仪和Reticon探测器获得了食双星AA UMa的高色散和高时间分辨率的光谱,并用交叉相关函数法测得其视向速度。从光谱特征来看,AA UMa是一对W UMa型食双星。本文首次给出了AA UMa的分光轨道解。在圆周运动的假设下,轨道根数测定为:P=0.468171天;T_0(相应于测光主极小时刻)=HJD2,446,520.4448;K_1=124.0公里/秒;K_2=227.7公里/秒。像其他一些使用本方法获得分光轨道解的食双星一样,AA UMa系统的质心速度没有能够唯一地确定,但是V_0=-34.8公里/秒可能是一个较好的估值。根据分光轨道根数,本文给出了新的测光历元公式:HJD Min I=2,446,520,4448(8)+0.468171(48)·E。AA UMa两子星的光谱型十分相似,与变星总表(GCVS)所列的GoV相一致。两子星的质量比为0.54,星等差为0.36(～B)