Reanalysis of the orbital period variations of two DLMR overcontact binaries:FG Hya and GR Vir

We investigate orbital period changes of two deep, low mass ratio(DLMR) overcontact W UMa-type binaries, FG Hya and GR Vir. It is found that the orbital period of FG Hya shows a cyclic change with a period of P_(mod)= 54.44 yr. The cyclic oscillation may be due to a third body in an eccentric orbit, while the orbital period of GR Vir shows a periodic variation with a period of P_(mod)= 28.56 yr and an amplitude of A = 0.0352 d. The periodic variation of GR Vir can be interpreted as a result of either the light-time effect of an unseen third body or the magnetic activity cycle.     

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)     

A Period Study of the Rs CVn-Type Binary ER Vulpeculae

Many available published times of light minima of the late-type binary system ER Vul have been compiled and analyzed using a new method proposed by Kalimeris et al. (1994). It was shown that the orbital period of the system oscillation with a period of about 30.6 years and an amplitude of 3.2×10^-6 days while it undergoes a constant period decrease of about dP /P=7.84× 10^-8 day / year. The prospective physical mechanisms that could have modulated the orbital period behaviour (periodic or non-periodic), have been studied. We found that a combination of a magnetic activity cycle mechanism and an enhanced stellar wind could explain satisfactorily the period change.     

Orbital period changes of contact binary systems: direct evidence for thermal relaxation oscillation theory

Orbital period changes of ten contact binary systems (S Ant, ε CrA, EF Dra, UZ Leo, XZ Leo, TY Men, V566 Oph, TY Pup, RZ Tau and AG Vir) are studied based on the analysis of their     curves. It is discovered that the periods of the six systems, S Ant, ε CrA, EF Dra, XZ Leo, TY Men and TY Pup, show secular increases. For UZ Leo, its secular period increase rate is revised. For the three systems, V566 Oph, RZ Tau and AG Vir, weak evidence is presented that a periodic oscillation (with periods of 20.4, 28.5 and 40.9 yr respectively) is superimposed on a secular period increase. The cyclic period changes can be explained by the presence of an unseen third body in the three systems. All the sample stars studied are contact binaries with     .
Furthermore, orbital period changes of 27 hot contact binaries have been checked. It is found that, apart from AW UMa with the lowest mass ratio     , none shows an orbital period decrease. The relatively weak magnetic activity in the hotter contact binaries means little angular momentum loss (AML) from the systems via magnetic stellar winds. The period increases of these W UMa binaries can be explained by mass transfer from the secondary to the primary components, which is in agreement with the prediction of the thermal relaxation oscillation (TRO) models. This suggests that the evolution of a hotter W UMa star is mainly controlled by TRO. On the other hand, for a cooler W UMa star     , its evolution may be TRO plus AML, which coincides with the recent results of Qian.     

Orbital Period Studies of the RS CVn-Type BinariesII. UV Piscium

Many available published times of light minima of the active binary system UV Psc have been collected and analyzed using a new method proposed by Kalimeris et al. (1994). Similar to what was seen in other RS CVn-type binaries, the orbital period of UV Psc oscillates with a period of about 61 years and an semi-amplitude of 0.21 ×10^-5 days. Two possible mechanisms (magnetic activity cycle mechanism and a light-time effect due to a hypothetical third body) that could modulated the orbital period behaviour are studied. We think that the cyclical period change in UV Psc can most probably be attributed to a magnetic activity cycle in the primary component. This revised version was published online in July 2006 with corrections to the Cover Date.     

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 intriguing orbital period variability of Y Leonis

The orbital period variation of the oEA system Y Leo is revised by taking into account new times of minimum light covering an extended time base of 101.8 yr. A multiperiodic ephemeris was finally established by carefully approaching the problem of periodicity detection for the considered periodic components. A method relying on Monte Carlo simulations was applied. The problem of the long-term behaviour of the O–C curve was taken into account using parabolic, and parabolic + periodic ephemerides. The physical interpretation of the mathematical models describing both long- and short-term behaviour of the O–C curve was performed by considering different mechanisms: the conservative mass transfer, the light-time effect, and the orbital period modulation through the cyclic magnetic activity of the late spectral type secondary component in the system. The consequences of these interpretations are rather intriguing and emphasize the need of new and detailed observational studies on Y Leo.     

Photometric observations and orbital period variations of HS 0705 + 6700 and NY Vir

We present photometric observations of two post-common-envelope stars, NY Vir (=PG 1336-018) and HS 0705 + 6700. The V band CCD observation of NY Vir was performed by a 40 cm telescope at Ege University Observatory and the R band observations of HS 0705 + 6700 were performed by 100 cm telescope at TÜB?TAK National Observatory. The new light curves were analyzed by the WD code and the physical parameters of stars were determined. We obtained new mid-eclipse timings for HS 0705 + 6700 and combined them with those previously published data. The analysis of the O-C residuals yields a period of about 8.06 ± 0.28 yr and an amplitude of 98.5 s for the system HS 0705 + 6700, which is attributed to the third star physically bounded to the evolved eclipsing pair. A mass function of 1.2 × 10⁻⁴ M_⊙ for the third star is obtained. The existence of a third star is also confirmed by the light curve analysis, indicating light contribution of about 0.043 at phase 0.25 in R-bandpass of the eclipsing pair. Using mass-luminosity relationship of the low mass stars we estimate a mass of 0.12 M_⊙ with an orbital inclination of about 20°. The O-C residuals obtained for the system NY Vir were represented by a downward parabola which indicates orbital period decrease in the system. Using the coefficient of quadratic term we calculate a rate of orbital period decrease of about dP/dt = −4.09 × 10⁻⁸days yr⁻¹. The period decrease we have measured in NY Vir may be explained by angular momentum loss from the binary system.     

Variation of the period and light curves of the solar-type contact binary EQ Tauri

We present two new sets of complete light curves of EQ Tauri (EQ Tau) observed in 2000 October and 2004 December. These were analysed, together with the light curves obtained by Yang & Liu in 2001 December, with the 2003 version of the Wilson–Devinney code. In the three observing seasons, the light curves show a noticeable variation in the time-scale of years. The more massive component of EQ Tau is a solar-type star (G2) with a very deep convective envelope, which rotates about 80 times as fast as the Sun. Therefore, the change can be explained by dark-spot activity on the common convective envelope. The assumed unperturbed part of the light curve and the radial velocities published by Rucinski et al. were used to determine the basic parameters of the system, which were kept fixed for spot modelling in the three sets of light curves. The results reveal that the total spotted area on the more massive component covers 18, 3 and 20 per cent of the photospheric surface in the three observing seasons, respectively. Polar spots and high-latitude spots are found. The analysis of the orbital period has demonstrated that it undergoes cyclical oscillation, which is due to either a tertiary component or periodic magnetic activity in the more massive component.     

Period investigation of two RS CVn-type binary stars: RU Cancri and AW Herculis

Orbital period variations of two RS CVn-type binaries, RU Cnc and AW Her, are presented based on the analysis of all available times of light minima. It is discovered that the orbital period of RU Cnc shows two possible period oscillations with periods of 13.38(±0.23) and 37.6(±3.4) years. The corresponding amplitudes of the oscillations are about 0.0098(±0.0023) and 0.0119(±0.0017) days. For AW Her, it is found that the period shows a cyclic variation with a period of 12.79(±0.34) years and an amplitude of about 0.0327(±0.0063) days. Since RU Cnc and AW Her are two RS CVn-type systems, the cyclic period oscillations are more likely to be caused by the magnetic activity cycles.     

Search for orbital motion of the pulsar 4U 1626–67: Candidate for a neutron star with a supernova fall-back accretion disk

We report here results from a new search for orbital motion of the accretion powered X-ray pulsar 4U 1626–67 using two different analysis techniques. X-ray light curve obtained with the Proportional Counter Array of the Rossi X-ray Timing Explorer during a long observation carried out in February 1996, was used in this work. The spin period and the local period derivative were first determined from the broad 2–60 keV energy band light curve and these were used for all subsequent timing analysis. In the first technique, the orbital phase dependent pulse arrival times were determined for different trial orbital periods in the range of 500 to 10,000 s. We have determined a 3σ upper limit of 13 lt-ms on the projected semimajor axis of the orbit of the neutron star for most of the orbital period range, while in some narrow orbital period ranges, covering about 10% of the total orbital period range, it is 20lt-ms. In the second method, we have measured the pulse arrival times at intervals of 100 s over the entire duration of the observation. The pulse arrival time data were used to put an upper limit on any periodic arrival time delay using the Lomb-Scargle periodogram. We have obtained a similar upper limit of 10 lt-ms using the second method over the orbital period range of 500–10,000 s. This puts very stringent upper limits for the mass of the compact object except for the unlikely case of a complete face-on orientation of the binary system with respect to our line-of-sight. In the light of this measurement and the earlier reports, we discuss the possibility of this system being a neutron star with a supernovae fall-back accretion disk.     

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)     

Period study of the binary star SW Cygni

The O−C curve of SW Cyg between 1880 and 1977 is presented and discussed. It is found that the orbital period undergoes a systematic change, becoming greater with time. In addition, a periodic oscillation of amplitude 0 _. ^d 015 with period of 43.8 years is superimposed on this general trend. It is concluded that the increase in the period is due to a transfer of mass from the secondary star to the primary and the periodic oscillation is due to the light time effect of the third body of mass functionf(m)=0.006M _⊙.     

First multi-color photometric investigation of the shortest-period semi-detached binary SWASPJ222302.02+195031.8

SuperWASPJ222302.02+195031.8 is an eclipsing binary with an orbital period about 0.22517657 days that is close to the short-period limit of contact binaries. Multi-color photometric light curves of the short-period binary in B, V, R_c and I_c bands are presented and analyzed by using the Wilson–Devinney (W–D) method. It is discovered that the system is a semi-detached binary where the secondary component is already filling the critical Roche lobe, while the primary is filling just 77.1% of its Roche lobe. The temperature of the primary is about 4300 K, and the temperature difference between the two components is about 500 K. The asymmetries in the light curves are explained by the coverage of stellar dark spots on the less massive component via magnetic activity. An analysis of all available eclipse times suggests that there are no any changes in the O-C diagram. This may indicate that there are no mass transfers between the two components. The semi-detached configuration with the dark spot on the surface of the lobe-filling secondary and no variations in the orbital period make the binary an interesting target for further investigations.     

Possible third body effects in the period changes of four Algol binaries: RY Aqr,SZ Her,RV Lyr and V913 Oph

An investigation of the orbital period changes of the neglected eclipsing binaries, RY Aqr, SZ Her, RV Lyr and V913 Oph, is presented based on all published minima times. Although the explanation of magnetic activity on the surface of the secondaries of the studied Algols is still open, the preferred light‐time effect due to the unseen components around the systems seems more plausible in explaining the tilted sinusoidal variations with relatively high‐amplitudes. The minimal mass values of possible tertiary components have been estimated to be about 1.06, 0.25, 0.78 and 2.85 M_⊙ for RY Aqr, SZ Her, RV Lyr and V913 Oph, respectively and the results indicate that their contributions to the total light of the eclipsing pairs are measurable with high accuracy photometric and spectroscopic data, if they exist. Applegate's (1992) model has been discussed as an alternative mechanism assuming that the cooler components have magnetic cycles. It is found that the model parameters of RY Aqr and V913 Oph are consistent with the required values in Applegate's model. In addition to the first detailed orbital study on these systems, a statistical survey on the character of the O – C variations of classical Algols has revealed that about 50 percent of the systems show cyclic behavior. This means that the presence of possible third bodies around classical Algols should be tested with careful analysis using new data. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

On activity periods of the April Lyrids

The activity of the Lyrid meteor shower is analyzed by visual observations in the interval 1900–2007. Processing of observations over a long time interval confirmed the presence of two periods of activity of the shower, of 12 and 60 years. These periods almost coincide with the period and five times Jupiter’s orbital period, i.e., 11.8 and 59.3 years, respectively, suggesting the possible influence of Jupiter on the shower structure. High activity of the shower is observed when the epoch of observations and the commensurate moment coincide with the orbital period of Jupiter and can be registered in the next 1–2 years. The increased activity of Lyrid by visual observations suggests that ZHR exceeds 30 meteors per hour. The modeling of activity profiles of showers for different minimum masses of meteoroids has shown that there is a correlation between the longitude of the node from the orbit with the mass of particles.     

Systematics of superoutbursts in dwarf novae

Photometric properties of known and suspected members of the SU UMa subclass of dwarf novae are tabulated and discussed. The precessing disc model of superoutbursts gives a satisfactory quantitative explanation of the periods of superhumps and their changes during superoutburst. The systems such as WZ Sge and HV Vir that have very long intervals between superoutbursts are deduced to be beyond the orbital period minimum, and have degenerate secondaries. The systems such as V1159 Ori that have extremely short recurrence times have high rates of mass transfer and are the equivalent of the Z Cam subclass that occurs at longer orbital periods.A simplified analytical approach to the theory of accretion discs is able to explain the correlations between normal and superoutburst recurrence times. It also explains the slope of the plateau region of superoutbursts, and why the slope is shallower in the very short recurrence time systems.     

An Investigation of the Physical Mechanisms of Orbital Period Variations of the Semidetached Binary UW Vir

The orbital period variations of the Algol-type semidetached binary UW Vir are analyzed. It is shown that in addition to a long-term rapid increase (dP/dt = + 1.37 × 10⁻⁶ day/year), its orbit period has a variation with the period of 62.3 years. Based on the basic physical parameters given by Brancewicz and Dworak in 1980, the physical mechanisms causing the orbital period variations are investigated. The analysis indicates that the periodical variation of orbital period can be interpreted by the light-travel time effect due to the presence of a third body with the mass of M₃ ≥ 0.94 M. As no observational information has been reported for this tertiary component, it might be a compact object (e.g., a white dwarf). The long-term increase of orbital period can be explained in terms of the mass transfer from the secondary to the primary component (dM₂/dt = 1.43 × 10⁻⁷ M/year). This is in agreement with the semidetached configuration of the system with a lobe-filling secondary component. But according to the evolution theory of binaries, the Algol-type semidetached binary UW Vir should be at the evolutionary stage of slow mass transfer on the nuclear-reaction timescale of the secondary component. However, the analysis shows that the timescale for the periodical variation of orbital period is much shorter than the nuclear-reaction timescale of the secondary component, but close to the thermodynamic timescale of the secondary. This reveals that: (1) This binary system is at the evolutionary stage of rapid mass transfer on the thermodynamic timescale of the secondary component; or (2) The circumstellar matter of the system makes a contribution to the rapid increase of orbital period via the angular momentum transfer.     

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)     

Photometric study of neglected eclipsing binary GSC 3576-0170

The new multi-color BVRI photometric light curves of the short-period eclipsing binary GSC 3576-0170 were obtained on two consecutive nights (October 5 and 6, 2009). With the 2003 version of Wilson–Devinney program, the precise photometric solutions are derived for the first time. The result shows that GSC 3576-0170 is a semi-detached binary system with a large temperature difference of approximately 1490 K. The light-curve distortions are further explained by a hot spot on the secondary component through mass transfer via a stream hitting the facing surface of the secondary component. By analyzing all available light minimum times, we also derived an update ephemeris and found for the first time a possible periodic oscillation with an amplitude of 0.0038 days and a period of 4.3 years. The periodic oscillation could be explained either by the light-time effect due to a presumed third component or by magnetic activity cycle of the system.