The eclipsing active star SV Camelopardalis

We present analysis and spot solutions based on yet unpublished B and V photoelectric observations on the active binary system SV Cam, carried out at Piszkéstető Mountain Station of Konkoly Observatory Budapest. The present spot solutions are based on the observed light curves in September 1993 and July 1994. Comparison of recent and older spot solutions – taken from the literature – suggests long term differences, but these divergences might be caused by some differences of the applied computational methods. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Cyclic light and period variations of the UV Leonis system

Solutions of the new standard V‐light curves for the EA type binary UV Leo are obtained using the PHOEBE code (0.31a version). Absolute parameters of the stellar components were then determined, enabling them to be positioned on the absolute magnitude‐color (l.e. M_V vs. B – V) isochrones diagram, based on which the age of the system is estimated to be >4×10⁹ yr. Also times of minima data (“O – C curve”) have been analyzed. Apart from an almost sinusoidal variation with a period of 29.63 yr, which modulates the orbital period, and was attributed to a third body orbiting around the system, other cyclic variation in the orbital period and also brightness, with time scales of 24.25 and 22.77 yr were found, respectively. We associate this with a magnetic activity cycle newly reported here for UV Leo (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Hubble Space Telescope observations of SV Cam – I. The importance of unresolved star-spot distributions in light-curve fitting

We have used maximum entropy eclipse-mapping to recover images of the visual surface brightness distribution of the primary component of the RS CVn eclipsing binary SV Cam, using high-precision photometry data obtained during three primary eclipses with Space Telescope Imaging Spectrograph aboard the Hubble Space Telescope ( HST ). These were augmented by contemporaneous ground-based photometry secured around the rest of the orbit. The goal of these observations was to determine the filling factor and size distribution of star-spots too small to be resolved by Doppler imaging. The information content of the final image and the fit to the data were optimized with respect to various system parameters using the χ² landscape method, using an eclipse-mapping code that solves for large-scale spot coverage. It is only with the unprecedented photometric precision of the HST data (0.000 15 mag) that it is possible to see strong discontinuities at the four contact points in the residuals of the fit to the light curve. These features can only be removed from the residual light curve by the reduction of the photospheric temperature, to synthesize high unresolvable spot coverage, and the inclusion of a polar spot. We show that this spottedness of the stellar surface can have a significant impact on the determination of the stellar binary parameters and the fit to the light curve by reducing the secondary radius from  0.794 ± 0.009  to  0.727 ± 0.009 R_⊙  . This new technique can also be applied to other binary systems with high-precision spectrophotometric observations.     

Analysis of the photoelectric light curve and the orbital period variations of the binary system UU Andromedae

In this work, the analysis of the photoelectric light curve (LC) in the broad‐band filter (400–700 nm) for the UU And system was carried out using the PHOEBE program (vers. 0.31a). The absolute dimensions of the system are determined and its evolution is discussed. Moreover, the period changes of the system are studied using updated O – C data, which shows a cyclic change with a period of P_mod = 18 yr. This was attributed to a magnetic activity cycle operating in this system. In addition to the cyclic change, a long‐term secular variation due to mass transfer from the secondary to the primary component with a rate of 6.17×10^–9 M_⊙ yr^–1 was also detected. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Orbital elements of the RS CVn eclipsing binary,SV Camelopardalis

The extensiveUBV observations of SV Camelopardalis by Patkos (1982) have been analysed to derive the orbital elements of the system. The data were corrected for the effect of third body (Sarma, Sarma & Abhyankar 1985) and for the ‘RS CVn’ distortion wave (Sarma, Vivekanandarao & Sarma 1988). The cleaned data were used to obtain a preliminary solution by a modified version of Wellmann method (Sarma & Abhyankar 1979) from which we concluded that the primary eclipse is a transit. The final orbital elements of SV Cam were obtained by the modified version (Sarma 1988; Sarmaet al. 1987) of WINK program by Wood (1972). The colour and median brightness variation are discussed. From the spectroscopic mass functionf(m) = 0.118 M_⊙ (Hiltner 1953), the absolute dimensions of the components are found to be 0.826 M_bd & 0.592 M_⊙ and 1.236 R_⊙ & 0.778 R_⊙ for the primary and secondary components, respectively. The age of the binary system is estimated to be 6.0 ± 1.0 × 10⁸ years     

A study of the distortion wave in the RS CVn eclipsing binary SV Camelopardalis

The light outside the eclipses of the totally eclipsing RS CVn binary SV Camelopardalis (SV Cam) is Fourier analysed and the amplitudes of the distortion waves have been derived. The distribution of the percentage contributions of these amplitudes inV, B andU colours with respect to the luminosities of the binary components indicates that the hotter component is the source of the distortion waves. These distortion waves, attributed to star spots, are modelled according to Budding (1977) and spot parameters like longitude, latitude, temperature and size are obtained. From this study it is noticed that while symmetric waves with two minima could be fitted satisfactorily, asymmetric waves with more than two minima could not be fitted well. From the longitudes of the minima of the best fitted curves, migration periods of four spot groups are determined. Assuming synchronism between rotation and orbital periods, the rotation periods of the four spot groups are derived from their migration periods. The period of rotation of one of the spot groups having direct motion is found to be 0^d.5934209 while the periods of the other three spot groups having retrograde motion are 0^d.5926588, 0^d.592607 and 0^d.5924688. As the latitudes of these spots are known from modelling parameters, the latitude having a rotation period equal to that of the orbital period (co-rotating latitude) is found to be about 30°     

Light and period study of the ecipsing binary system TW Andromedae

Photoelectric light curve (LC) solutions of the close binary system TW And were obtained using the PHOEBE program (version 0.31a). Absolute parameters of the stellar components were then determined, enabling us to discuss the structure and evolutionary status of TW And. The configuration of the system based on the LCs solutions indicates that the secondary component is slightly detached from its critical Roche surface. In addition, times of minima data (“O –C curve”) were analyzed. Apart from an almost parabolic variation of the general trend of the O –C data, indicative of a secular increase in the orbital period with a rate 0.032 s yr^–1, which was attributed to a mass transfer with a rate of Δm₂ = –1.10 × 10^–10 M_⊙ yr^–1. Additionally, a sinusoidal variation with a period of 52.75 ± 1.80 yr, modulating the orbital period, was found, which we attribute to a third body orbiting the system. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Possible connection between period change and magnetic activity of the very short‐period binary VZ Piscium

New times of light minimum of the short‐period (P = 0^d.26) close binary system, VZ Psc, are presented. A period investigation of the binary star, by combining the three new eclipse times with the others collected from the literatures, shows that the variation of the period might be in an alternate way. Under the hypothesis that the variation of the orbital period is cyclic, a period of 25 years and an amplitude of 0.^d0030 for the cyclic change are determined. If this periodic variation is caused by the presence of a third body, the mass of the third body (m₃) should be no less than 0.081M_⊙. Since both components of VZ Psc are strong chromospherically active and the level of activity of the secondary component is higher than that of the primary one, the period may be more plausibly explained by cyclic magnetic activity of the less massive component. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The short‐period low‐mass binary system CC Com revisited

In this study we determined precise orbital and physical parameters of the very short‐period low‐mass contact binary system CC Com. The parameters are obtained by analysis of new CCD data combined with archival spectroscopic data. The physical parameters of the cool and hot components are derived as M_c = 0.717(14) M_⊙, M_h = 0.378(8) M_⊙, R_c = 0.708(12) R_⊙, R_h = 0.530(10) R_⊙, L_c = 0.138(12) L_⊙, and L_h = 0.085(7) L_⊙, respectively, and the distance of the system is estimated as 64(4) pc. The times of minima obtained in this study and with those published before enable us to calculate the mass transfer rate between the components which is 1.6 × 10^–8 M_⊙ yr^–1. Finally, we discuss the possible evolutionary scenario of CC Com (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

First light curve and period study of LO Andromedae

New BV light curves and times of minimum light for the short period W UMa system LO And were analyzed to derive the preliminary physical parameters of the system. The light curves were obtained at Ankara University Observatory during 5 nights in 2003. A new ephemeris is determined for the times of primary minimum. The analysis of the light curves is made using the Wilson‐Devinney 2003 code. The present solution reveals that LO And has a photometric mass ratio q = 0.371 and is an A‐type contact binary. The period of the system is still increasing, which can be attributed to light‐time effect and mass transfer between the components. With the assumption of coplanar orbit of the third body the revealed mass is M₃ = 0.21M_⊙. If the period change dP/dt = 0.0212 sec/yr is caused only by the mass transfer between components (from the lighter component to the heavier) the calculated mass transfer rate is dm/dt = 1.682×10⁻⁷M_⊙/yr. The absolute radii and masses estimated for the components, based on our photometric solution and the absolute parameters of the systems which have nearly same period are R₁ = 1.30R_⊙, R₂ = 0.85R_⊙, M₁ = 1.31M_⊙, M₂ = 0.49M_⊙ respectively for the primary and secondary components. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Orbital period variation of the eclipsing binary system TT Herculis

New photoelectric UBV observations were obtained for the eclipsing binary TT Her at the Ankara University Observatory (AUO) and three new times of minima were calculated from these observations. The (O – C) diagram constructed for all available times of minima of TT Her exhibits a cyclic character superimposed on a quadratic variation. The quadratic character yields an orbital period decrease with a rate of dP /dt = –8.83 × 10^–8 day yr^–1 which can be attributed to the mass exchange/loss mechanism in the system. By assuming the presence of a gravitationally bound third body in the system, the analysis of the cyclic nature in the (O – C) diagram revealed a third body with a mass of 0.21M_⊙ orbiting around the eclipsing pair. The possibility of magnetic activity cycle effect as a cause for the observed cyclic variation in the (O – C) diagram was also discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

An orbital period investigation of the Algol-type eclipsing binary VW Hydrae

Orbital period variations of the Algol-type eclipsing binary, VW Hydrae, are analyzed based on one newly determined eclipse time and the other times of light minima collected from the literature. It is discovered that the orbital period shows a continuous increase at a rate of dP/dt = +6.34×10-7 d yr-1 while it undergoes a cyclic change with an amplitude of 0.0639 d and a period of 51.5 yr. After the long-term period increase and the large-amphtude period oscillation were subtracted from the O-C curve, the residuals of the photoelectric and CCD data indicate a small-amplitude cyclic variation with a period of 8.75 yr and a small amplitude of 0.0048d. The continuous period increase indicates a conservative mass transfer at a rate of dM2/dt = 7.89×10-8 M⊙ yr-1 from the secondary to the primary. The period increase may be caused by a combination of the mass transfer from the secondary to the primary and the angular momentum transfer from the binary system to the circumbinary disk. The two cyclic period oscillations can be explained by light-travel time effects via the presence of additional bodies. The small-amplitude periodic change indicates the existence of a less massive component with mass M3 > 0.53 M⊙, while the large-amplitude one is caused by the presence of a more massive component with mass M4 > 2.84 M⊙. The ultraviolet source in the system reported by Kviz & Rufener (1987) may be one of the additional components, and it is possible that the more massive one may be an unseen neutron star or black hole. The rapid period increase and the possibility of the presence of two additional components in the binary make it a very interesting system to study. New photometric and high-resolution spectroscopic observations and a detailed investigation of those data are required in the future.     

The short-period end of the contact binary period distribution based on the All-Sky Automated Survey

The search volume-corrected period distribution of contact binaries of the W UMa type appears to reflect primarily the constant number ratio of ≃1/500 to the number of stars along the main sequence; there exist no evidence for angular momentum evolution. The maximum in contact binary numbers is located at shorter periods than estimated before,   P ≃ 0.27 d  . The drop in numbers towards the cut-off at   P ≃ 0.215–0.22  d still suffers from the small number statistics while the cut-off itself remains unexplained. Only one out of seven short-period All-Sky Automated Survey variables with   P < 0.22 d  have been retained in the sample considered here within  8 < V < 13  ; this short-period field-sky record holder at   P = 0.2178 d  should be studied.     

Multiple frequency analysis of the large-amplitude SX Phoenicis star BL Camelopardalis

A multifrequency analysis of the SX Phoenicis star BL Camelopardalis is presented on the basis of new high-speed photometry, along with fitting a total of 136 maxima. BL Cam is a multiple periodic pulsator. We find f ₀=25.5768, f ₁=25.2982, f ₂=25.8622, f ₃=31.5912, f ₄=25.1065, f ₅=25.5147 and f ₆=25.6188 cycle d⁻¹ together with the harmonics 51.1513 and 76.7268 cycle d⁻¹ and combination frequencies f ₀+ f ₁, f ₀+ f ₂ and f ₀+ f ₃. The new frequency solution represents the light curves of BL Cam quite well. The observed minus calculated (O-C) analysis indicates that the fundamental frequency is in good agreement with the results of Fourier analysis.