The Eccentric Eclipsing Binary V889 Aquilae

Several new times of minimum light recorded with photoelectric or CCD means have been gathered for the eccentric eclipsing binary V889 Aql (P = 11.1 days, e = 0.37). Its O–C diagram is presented, and improved elements of the apsidal motion and the light-time effect (LITE) are given. We found a long apsidal motion period of about 24 400 ± 2400 years and a period of the third body of about 52 ± 2 years.     

Updated UBV Light-Curve and Period Analysis of Eclipsing Binary HS Herculis

UBV light-curves of the eclipsing binary HS Herculis, obtained in 2002–2003 observational seasons, were analysed with Wilson-Devinney computer code. New absolute dimensions of the system were calculated using the results of the light-curve analysis. Period variation of the system was also investigated. Several new times of minima have been secured for this problematic system. An apsidal motion with a period of 80.7 years was confirmed and a third body in a pretty eccentric orbit (e ₃ = 0.90 ± 0.08) with a period of 85.4 years was found. The corresponding internal structure constants of the binary system, log k ₂, and the mass of the third body were derived.     

The Period Variation of V839 Oph

In this study we present the results of the preliminary analysis of the period variation of V839 Oph based on the extensive series of minima times collected from the literature. The character of the (O–C) diagram can be approximated with a cyclic variation superimposed on a quadratic variation. The quadratic variation can be explained in terms of mass exchange/loss mechanism in the system, while the cyclic variation could be attributed to the light-time effect of a gravitationally bound third body to the system or the magnetic activity cycle of the primary component.     

Rapid apsidal motion in V381 Cassiopeiae

V381 Cas is a relatively bright and early-type eclipsing binary system. Several new times of its eclipses were measured as part of our long-term observational project of eccentric eclipsing binaries. Based on a current O–C diagram solution, we found for the first time that its orbit is slightly eccentric (e = 0.025) and shows a very rapid apsidal advance with short period of about 20 years only. The relativistic and third body effects are negligible, being about 3% of the total apsidal motion rate.     

Eccentric Eclipsing Binary YY Sagittarii

Seven new precise times of minimum light have been gathered for the triple eccentric eclipsing binary YY Sgr (P = 2^d.63, e = 0.16). Its O--C diagram is presented and improved elements of the apsidal motion and the light-time effect are given. We found a new short period of the third body of about 18.5 years in an eccentric orbit (e ₃ ≃ 0.4).     

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)     

Possible Light-Time Effect in the Eclipsing Binary System TY Boo

The O − C diagram for the eclipsing binary system TY Boo was constructed with the new minima times observed at the Ankara University Observatory along with the collected ones from the literature. The O − C diagram shows a cyclic variation superimposed on a quadratic variation. The quadratic variation can be explained in terms of mass loss/exchange mechanism in the system while the cyclic variation is attributed to a possible light-time effect caused by a third body revolving around the close binary.     

Cyclic variations of the period and luminosity of SV Camelopardalis

New standardized V ‐band light curves (LCs) for the eclipsing binary SV Cam have been modeled using the PHOEBE program (v. 0.31a). Absolute parameters of the stellar components were then determined, enabling them to be positioned on the mass‐radius diagram. Analysis of eclipse minima timing data (O – C diagrams) indicated two cyclic periods of 48.0 and 23.3 yr. These cyclic variations of the orbital period are interpreted in terms of motion of a third body around the system and magnetic activity cycle modulating the orbital period of SV Cam via the Applegate (1992) mechanism. The use of the Applegate model for SV Cam has been checked by examining the long term brightness variation and calculating some important parameters of this system. The results of these calculations favor the modulation of the orbital period by the Applegate mechanism. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

On the apsidal motion of BP Vulpeculae

BP Vulpeculae is a bright eclipsing binary system showing apsidal motion. It was found in an earlier study that it shows retrograde apsidal motion which contradicts theory. In this paper we present the first BV light curve of the system and its light curve solution as well as seven new times of the minima from the years 1959–1963. This way we could expanded the baseline of the investigation to five decades. Based on this longer baseline we concluded that the apsidal motion is prograde agreeing with the theoretical expectations and its period is about 365 years and the determined internal structure constant is close to the theoretically expected one.     

Detailed period study of Delta Capricorni

Detailed period study of the eclipsing binary system Delta Cap is presented. Available times of minima have been classified, and two minima have been found off the instant period trend. A new period of 1.^d0227789 has been given. Period changes in different portions of the O?C diagram have been estimated, which range from 6.4×10^?6 d to 1.8×10^?3 d (?), the average being 3.5×10^?5 d. A sinusoidal variation is evident in the O?C diagrams, which is indicative of the possible presence of a third body, having a period of nearly 62 years, however, it is yet to be confirmed.     

A new period and period changes in VZ Hydrae

A new period (P=2 _. ^d 9042997) of the eclipsing binary system VZ Hydrae has been given, which is based on all the available times of minima. The period based on the photoelectric epochs has also been presented. The O?C diagram and detailed period study of VZ Hya have been presented for the first time, and the period changes have been estimated in different portions of the O?C diagram. Significant period changes do not appear to have occurred in VZ Hya, however, the O?C diagram suggests that the period of the system shows a slow tendency to increase. Period changes of 10^?5 d (?) to 10^?7 d have occurred around the years 1933, 1971, and 1975. All four period changes are noted in the time-interval 1918 to 1978. Upward treands appear stronger than the declining trends. Secondary minima show larger fluctuations than the primary minima. The fluctuations of the O?C values around the zero-line of VZ Hya demands notice for searching out the cause of period variations such as the presence of a third body.     

First ground‐based photometry and light‐curve analysis of the eccentric eclipsing binary V744 Cas

The first ground‐based BVR photometric observations of the recently discovered eclipsing binary V744 Cas are presented. From these measurements, timings for two primary and one secondary minima have been calculated. The light curves of the system were analyzed by using the Wilson‐Devinney program. The analysis shows that the system is detached with two similar components of spectral type A2V, and the orbit is eccentric (e = 0.0662 ± 0.0005). The longitude of the periastron (ω) was found significantly different for two different light curves (ours and that of Hipparcos), which is strongly suggestive of an apsidal motion with a period of about 425 ± 68 yr. This makes V744 Cas an important candidate for studies of apsidal motions. The first estimate of the absolute dimensions place the system close to the terminal age of the main sequence (TAMS) in the HR diagram. The distance from the spectroscopic parallax (d = 740 ± 10 pc) was found to be slightly larger than the Hipparcos distance of d = 610 ± 400 pc. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Cyclic period changes and the light-time effect in eclipsing binaries: A low-mass companion around the system VV Ursae Majoris

In this article, a period analysis of the late-type eclipsing binary VV UMa is presented. This work is based on the periodic variation of eclipse timings of the VV UMa binary. We determined the orbital properties and mass of a third orbiting body in the system by analyzing the light-travel time effect. The O−C diagram constructed for all available minima times of VV UMa exhibits a cyclic character superimposed on a linear variation. This variation includes three maxima and two minima within approximately 28,240 orbital periods of the system, which can be explained as the light-travel time effect (LITE) because of an unseen third body in a triple system that causes variations of the eclipse arrival times. New parameter values of the light-time travel effect because of the third body were computed with a period of 23.22 ± 0.17 years in the system. The cyclic-variation analysis produces a value of 0.0139 day as the semi-amplitude of the light-travel time effect and 0.35 as the orbital eccentricity of the third body. The mass of the third body that orbits the eclipsing binary stars is 0.787 ± 0.02 M_⊙, and the semi-major axis of its orbit is 10.75 AU.     

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)     

RS CVn-binary RW com: A possible three-body system

A first detailed period study of the eclipsing RS CVn-binary system RW Com is presented. A new period (P=0^d.2373455) based on 223 minima is given. The O–C diagrams of RW Com have been presented for the first time. Types of ten minima have been corrected judging the period trend. Period changes in different portions of the O–C diagram (Figure 2) have been estimated. The total change in period (P/P) ranges from 5.5×10^–7 to 6.4×10^–6. Thus, P ranges from 1.3×10^–7 d to 1.5×10^–6 d. Numerous minima are available in the time interval 1967 to 1986. This part of the O–C diagram (Figure 2) shows a sinusoidal variation, thus, it is suspected that RW Com could be a three-body system. The period of variation due to third body appears to be nearly 16 years.     

ST Persei: A possible multi-body system

Detailed period study of the eclipsing binary ST Per is presented. A new period (P=2^d.648339) is given. Period changes in different portions of the O-C diagram with a new period have been estimated. The total changes in period (P) ranges from 2.17×10^–5d to 2.64×10^–4d which is appreciably large. Sufficient number of minima in the time interval 1934 to 1985 for this system are available. Distinct increasing and decreasing trends are evident, the change in the tendency appears to have occurred around 1947. Sinusoidal variation is seen between cycles 7000–10000, which indicates that ST Per is a three-body system, the period of the third body being about 22 years. However, the sinusoidal variation is not perfectly symmetric in shape, therefore, it is suspected that ST Per is a four-(or multi-) body system.     

A new light‐time effect study of AR Aurigae

A period study of the young binary AR Aur based on the extensive series of published photoelectric/ccd minima times indicates the cyclic (O – C) variation for the system. This continuous oscillatory variation covers almost three cycles, about 6000 orbital periods, by the present observational data. It can be attributed to the light‐time effect due to a third body with a period of 23.68 ± 0.17 years in the system. The analysis yields a light‐time semi‐amplitude of 0.0084 ± 0.0002 day and an orbital eccentricity of 0.20 ± 0.04. Adopting the total mass of AR Aur, the mass of the third body assumed in the co‐planar orbit with the binary is M₃ = 0.54 ± 0.03 M_⊙ and the semimajor axis of its orbit is a₃ = 13.0 + 0.2 AU. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

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)     

EM Cygni: A study of its eclipse timings

EM Cygni is a Z Cam‐subtype eclipsing dwarf nova. Its orbital period variations were reported in the past but the results were in conflict to each other while other studies allowed the possibility of no period variation. In this study we report accurate new times of minima of this eclipsing binary and update itsO –C diagram.We also estimate the mass transfer rate in EM Cygni system and conclude that the mass transfer is far from the critical value. The mass transfer rate determined from the eclipse timings is in agreement with the spectroscopically determined value. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Long‐term orbital period behaviors of the neglected Algol type binaries: CC Herculis and XZ Aquilae

Orbital period variations of two neglected Algol type binaries, CC Her and XZ Aql, are studied based on all available times of minima. In the case of CC Her, it is found that the O –C curve displays a tilted sinusoidal variation with an eccentricity of 0.54 ± 0.03 and a period of 52.4 ± 0.4 yr, which can be explained by the light‐time effect due to the presence of an unseen component. The course of the orbital period change in XZ Aql appears less reliable but its O –C curve can be represented by a periodic variation with a period of 36.7 ± 0.6 yr superimposed on an upward parabola. The parabolic variation indicates a secular period increase with a rate of dP /dt = 7.1 s per century. The corresponding conservative mass transfer from less massive component to the more massive one is about 3.26 × 10^–7 M_⊙ yr^–1. It is interesting to see that the O –C variation of CC Her displays no evidence (as upward parabola) on the mass transfer characteristic for Algols. The periodic change of the orbital period of XZ Aql, like CC Her, may be caused by the presence of the thirdbody. The lower limits of the masses of the hypothetical unseen components for CC Her and XZ Aql are found to be 2.69 M_⊙ and 0.47 M_⊙, respectively. The third body of CC Her should be detectable not only spectroscopically but also photoelectrically, if it exists. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)