Radial velocity and light curves analysis of the eclipsing binary NN Vir

The eclipsing binary NN Vir is a short period system showing an EW‐type light curve. Photometric observations of NN Vir were done by Gomez‐Ferrellad & Garcia‐Melendo (1997) at Esteve Duran Observatory. We used photometric data of NN Vir for light curve analysis. The available spectroscopic data of NN Vir is new and we also used the first radial velocity data of this system obtained by Rusinski & Lu (1999) for analysis. The radial velocity and light curves analysis was made with the latest version ofWilson program(1998) and the geometric and physical elements of the system are derived. By searching the simultaneous solutions of the system, we have determined the masses and radii of the components : 1.89(M_⊙) and 1.65(R_⊙) for the primary component; 0.93(M_⊙) and 1.23(R_⊙) for the secondary component. We estimated effective temperatures of 7030(K) for the primary and 6977(K) for the secondary component. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The Algol-type eclipsing binaries RW CrB and VZ Leo: new RI photometric study and search for pulsations

In this study we present the new R and I light curve solutions for the eclipsing binary systems RW CrB and VZ Leo, which for VZ Leo is the first one in the literature. Our new observations have been analyzed using the Wilson-Devinney code from which new geometric and photometric elements are derived. The geometry of both stars is that of a semi-detached binary system where the secondary component fills its Roche lobe while the primary component is well inside. In the case of RW CrB, asymmetry in the light curve was explained by a spot model. The orbital period changes of both systems were studied and the results indicated a period decrease which can be explained by angular momentum loss. We also investigated the possibility of pulsations of the primary components since these systems are mentioned as candidates of δ Sct type pulsation. However, a time-series analysis of the residual curves in the filter I does not indicate any evidence of periodic light variation for both systems. Finally, we compared the results obtained for both binary stars to those of similar systems.     

A photometric study of the contact binary AZ Virginis

New light curves and photometric solutions of the contact binary AZ Vir are presented in this paper. The light curves appear to exhibit a typical O'Connell effect, with Maximum I being 0.021 mag (V) and 0.023 mag (B) brighter than Maximum II, respectively. From the observations, six times of minimum light were determined and from the present times of minimum light and those collected from the references, the light elements of the system were improved. The light curves were analyzed by means of the Wilson‐Devinney program. The results suggest that AZ Vir is a W‐subtype contact binary with a mass ratio of q = 0.623(2). The asymmetry of the light curves is explained by star spot models. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Radial Velocity and Light Curve Analysis of the Eclipsing Binary Nn Vir

The eclipsing binary NN Vir is a short period system showing an EW-type light curve. Photometric observations of NN Vir were done by Gomez–Ferrellad and Garcia–Melendo (1997) at Esteve Duran Observatory. The first spectroscopic observations of this system were obtained by Rucinski and Lu (1999). The radial velocity and light curves analysis was made with the latest version of the Wilson program (1998), and the geometric and physical elements of the system are derived. From the simultaneous solutions of the system, we determined the masses and radii of the components: 1.89 M _⊙ and 1.65 R _⊙ for the primary component; 0.93 M _⊙ and 1.23 R _⊙ for the secondary component. We estimated effective temperatures of 7030 K for the primary and 6977 K for the secondary component.     

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.     

Ccd Photometry of the Neglected Contact Binaries V344 Lac and V1191 Cyg

New photoelectric and CCD observations of the eclipsing contact binary systems V344 Lac and V1191 Cyg are presented and analyzed. All available times of minimum light were used to study period changes of the systems and determine up-to-date ephemerides. The orbital period of V1191 Cyg is found to be increasing at a very fast rate. The photometric elements were determined using the new light curve, radial-velocity curve and broadening function fitting code ROCHE.     

BV observations of W UMa-type binaries: CK Boo,BI CVn,and AH Vir

Photoelectric BV observations of W UMa-type binaries CK Boo, BI CVn, and AH Vir are presented, and light curve variations and shifts of minima are discussed in the context of stellar activity and mass transfer. The O–C increments in three systems were found to be 0.08, 0.80, and 0.60 s per revolution, respectively. The new ephemeris for the future observations were also found.     

Fourier analysis of the light curves of W UMa-type stars

The light curves of 30 well observed W UMa-type systems are analysed according to Kopal's method for the study of the light changes of eclipsing variables by using frequencydomain techniques. New geometric and photometric elements are derived and new values for the gravity-darkening coefficients are also given. Finally, an answer to the problem of whether or not these are contact systems is attempted.     

激变变星及相关天体的H_α与近红外电离钙三重线的光谱分析

给出了1997年4月15日至17日在北京天文台用2．16m望远镜卡焦光谱仪观测获得的6颗激变变星（ABBoo;UXUMa,TCrBAHHer,ZCam和V426Oph）及3颗相关天体（UMa3,EGUMa和Leo3）的CCD光谱,并同时拍摄了5颗晚型星（3Dra,Vir,Leo,34Boo和36Corn）的CCD光谱,作为晚型星参考谱．测量了观测样本星的Hα和近红外CaII的三重线（8498,8542和8662）的等值宽度（EW）,谱线半极大全宽（FWHM）和现向速度（Vr）,并分析了这些星的活动性．     

Photoelectric light curves of RT coronae borealis and their analysis

The first photoelectric light curves of the RS CVn-type eclipsing binary RT CrB are presented. There is no indication about the existence of wave like distortion on its light curve. The light curves were analyzed by using Wood's and Nelson, Davis, and Etzel's methods. The radii of the components are nearly identical. The solutions indicate that the cooler component has a later spectral type between K0 and K2.     

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.     

Long‐term photometry of three active red giants in close binary systems: V2253 Oph,IT Com and IS Vir

We present and analyze long‐term optical photometric measurements of the three active stars V2253 Oph, IT Com and IS Vir. All three systems are single‐lined spectroscopic binaries with an early K giant as primary component but in different stages of orbital‐rotational synchronization. Our photometry is supplemented by 2MASS and WISE near‐IR and mid‐IR magnitudes and then used to obtain more accurate effective temperatures and extinctions. For V2253 Oph and IT Com, we found their spectral energy distributions consistent with pure photospheric emission. For IS Vir, we detect a marginal mid‐IR excess which hints towards a dust disk. The orbital and rotational planes of IT Com appear tobe coplanar, contrary to previous findings in the literature. We apply a multiple frequency analysis technique to determine photometric periods, and possibly changes of periods, ranging from days to decades. New rotational periods of 21.55±0.03 d, 65.1±0.3 d, and 23.50±0.04 d were determined for V2253 Oph, IT Com, and IS Vir, respectively. Splitting of these periods led to tentative detections of differential surface rotations of δP/P ≈ 0.02 for V2253 Oph and 0.07 for IT Com. Using a time‐frequency technique based on short‐term Fourier transforms we present evidence of cyclic light variations of length ≈ 10 yr for V2253 Oph and 5–6 yr for IS Vir. A single flip‐flop event has been observed for IT Com of duration 2–3 yr. Its exchange of the dominant active longitude had happened close to a time of periastron passage, suggesting some response of the magnetic activity from the orbital dynamics. The 21.55‐d rotational modulation of V2253 Oph showed phase coherence also with the orbital period, which is 15 times longer than the rotational period, thus also indicating a tidal feedback with the stellar magnetic activity. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The solution parameters of very close binary systems

The problems encountered in the derivation of elements from the light curves of very close binary systems are discussed. It is shown that the rectification procedure is critically dependent on the underlying model. The assumption of a contact configuration leads to better coincidence of theoretical and observed light curves. The Fourier analysis method is used to derive the solution parameters of the examples YY Eri and AM Leo. Veröffentlichungen der Dr. Remeis Sternwarte Bamberg, Astronomisches Institut der Universität Erlangen-Nürnberg, volume 10, Nr. 112.     

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.     

XMM–Newton observations of UW CrB: detection of X-ray bursts and evidence for accretion disc evolution

UW CrB (MS 1603+2600) is a peculiar short-period X-ray binary that exhibits extraordinary optical behaviour. The shape of the optical light curve of the system changes drastically from night to night, without any changes in overall brightness. Here we report X-ray observations of UW CrB obtained with XMM–Newton . We find evidence for several X-ray bursts, confirming a neutron star primary. This considerably strengthens the case that UW CrB is an accretion disc corona system located at a distance of at least 5–7 kpc (3–5 kpc above the Galactic plane). The X-ray and Optical Monitor (ultraviolet–optical) light curves show remarkable shape variation from one observing run to another, which we suggest are due to large-scale variations in the accretion disc shape resulting from a warp that periodically obscures the optical and soft X-ray emission. This is also supported by the changes in phase-resolved X-ray spectra.     

XX Cam—The Inactive R CrB star

Infrared observations obtained six years apart of the R CrB type star XX Cam do not show any infrared excess, unlike all the other members of the class. The observed colours match a 7000 K black body energy distribution quite well. From the year 1898 till todate, apparently XX Cam has undergone only one visual light minimum in 1940. The lack of infrared excess, the abundance peculiarities and further lack of small amplitude light variations with periods of few tens of days, which are characteristic of R CrB type stars, are discussed in terms of theoretical pulsation models of helium stars.     

On properties of mass transfer in an Algol-type binary system:an example of VV Vir

Some properties of mass transfer within a semi-detached binary system are discussed based on an example of VV Vir.The observations and analysis of VV Vir show that it is a semi-detached binary system with the less massive cooler component filling its Roche lobe,which is also called an Algol-type binary system.Based on the parameters of this semi-detached binary,a theoretical study on the mass flow is carried out,including the trajectory of the mass flow,the position,radius and temperature of the impact spot caused by the mass flow,the inconsistent form of the mass flow and the possibly huge rate of energy transfer carried by the mass flow.Humps and distortions in light curves of VV Vir are deemed to be weak evidence for the theoretical results.     

New photoelectric observations of four W UMa systems: OO aql,V839 Oph,V566 Oph,and SW Lac

The W UMa-type systems (OO Aql, V839 Oph, V566 Oph, and SW Lac) were observed photoelectrically in two wavebands (B andV) during the years 1982–1983. The light curves of these systems are analysed using Kopal's frequency-domain technique and the optimisation method. New geometrical and physical elements have been determined. The absolute elements and the period variations of these systems are discussed.     

Molecule formation and cloud collapse

Ultraviolet spectra ofo And, CrB, Ori A and Vir, which were obtained with the S59 spectrometer at a resolution of 1.7 Å in three 100 Å wide regions centered at 2110, 2454 and 2825 Å, have been studied for the presence or the absence of the effects due to their binary nature. As may have been anticipated from their orbital and other characteristics, no indication of strong binary interactions were seen in these observations. However, there are certain spectral peculiarities suggesting the possibility of modifications of spectral classifications for some of these objects. A rather unusual spectral behavior in Vir is also noted. In addition, based primarily on the reviewing of the available literature, we draw new attention to a remarkable property of the third component in Ori A.     

Absolute parameters and physical nature of two W-UMa type binaries: V1123 Tau and V1128 Tau

We present high-precision,multi-band CCD photometry of two less-studied close binaries V1123 Tau and V1128 Tau.Complete covered light curves and a number of new times of light minima of the two eclipsing systems were obtained,based on which,revised orbital elements and new ephemerides were given.By adopting the Wilson-Devinney method,the light curves were analyzed.The photometric solutions confirm the W UMa-type nature of the binary systems.With the less-massive secondary slightly cooler than the primary,V1...