A. Erdem

Catalogue of Algol type binary stars

A catalogue of (411) Algol-type (semi-detached) binary stars is presented in the form of five separate tables of information. The catalogue has developed from an earlier version by including more recent information and an improved layout. A sixth table lists (1872) candidate Algols, about which fewer details are known at present. Some issues relating to the classification and interpretation of Algol-like binaries are also discussed.

A catalogue of chromospherically active binary stars (third edition)

The catalogue of chromospherically active binaries (CABs) has been revised and updated. With 203 new identifications, the number of CAB stars is increased to 409. The catalogue is available in electronic format where each system has a number of lines (suborders) with a unique order number. The columns contain data of limited numbers of selected cross references, comments to explain peculiarities and the position of the binarity in case it belongs to a multiple system, classical identifications (RS Canum Venaticorum, BY Draconis), brightness and colours, photometric and spectroscopic data, a description of emission features (Ca II H and K, Hα, ultraviolet, infrared), X-ray luminosity, radio flux, physical quantities and orbital information, where each basic entry is referenced so users can go to the original sources.

Analysis of the exoplanet containing system Kepler-91

We have applied the graphical user interfaced close binary system analysis program WinFitter to an intensive study of Kepler-91 using all the available photometry from the NASA Exoplanet Archive (NEA) at the Caltech website: http://exoplanetarchive.ipac.caltech.edu. Our fitting function for the tidal distortion derives from the relevant Radau equation and includes terms up to the fifth power of the fractional radius. This results in a systematic improvement in the mass ratio estimation over that of Lillo-Box et al. (Astron. Astrophys. 562:A109, 2014a) and our derived value for the mass ratio is in close agreement with that inferred from recent high-resolution spectroscopic data.It is clear that the data analysis in terms of simply an eclipsing binary system is compromised by the presence of significant other causes of light variation, in particular non-radial pulsations. We apply a low-frequency filtering procedure to separate out some of this additional light variation. Whilst the derived eccentricity appears then reduced, an eccentric effect remains in the light curve. We consider how this may be maintained in spite of likely frictional effects operating over a long time. There are also indications that could be associated with Trojan or other period-resonant mass concentrations. Suggestions of a possible secular period variation are briefly discussed.

The chromospherically active binary CF Tuc revisited

This paper presents results derived from analysis of new spectroscopic and photometric observations of the chromospherically active binary system CFTuc. New high-resolution spectra, taken at the Mt. John University Observatory in 2007, were analysed using two methods: cross-correlation and Fourier-based disentangling. As a result, new radial velocity curves of both components were obtained. The resulting orbital elements of CF Tuc are a 1 sin i = 0.0254 ± 0.0001 au, a 2 sin i = 0.0228 ± 0.0001 au, M 1 sin i = 0.902 ± 0.005 M ⊙ and M 2 sin i = 1.008 ± 0.006 M ⊙ . The cooler component of the system shows Hα and Ca II H&K emissions. Using simultaneous spectroscopic and photometric observations, an anticorrelation between the Hα emission and the BV light curve maculation effects was found. This behaviour indicates a close spatial association between photospheric and chromospheric active regions. Our spectroscopic data and recent BV light curves were solved simultaneously using the Wilson-Devinney code. A dark spot on the surface of the cooler component was assumed to explain large asymmetries observed in the light curves. The following absolute parameters of the components were determined: M 1 = 1.11 ± 0.01 M ⊙ , M 2 = 1.23 ± 0.01 M ⊙ , R 1 = 1.63 ± 0.02 R ⊙ , R 2 = 3.60 ± 0.02 R⊙, L 1 = 3.32 ± 0.51 L ⊙ and L 2 = 3.91 ± 0.84 L ⊙ . The primary component has an age of about 5 Gyr and is approaching its main-sequence terminal age. The distance to CF Tuc was calculated to be 89 ± 6 pc from the dynamic parallax, neglecting interstellar absorption, in agreement with the Hipparcos value. The orbital period of the system was studied using the O-C analysis. The O-C diagram could be interpreted in terms of either two abrupt changes or a quasi-sinusoidal form superimposed on a downward parabola. These variations are discussed by reference to the combined effect of mass transfer and mass loss, the Applegate mechanism and also a light-time effect due to the existence of a third body in the system.

Multi-Facility Study of the Algol-Type Binary δ Librae

Various branches of observational information, and related physical problems concerning the bright, relatively close, Algol binary δ Lib are discussed. Times of minimum light confirm the classical Algol status, which, combined with the optical and IR photometry of Lazaro et al. (2002), provide the basis for a good understanding of the system’s basic parameters. New spectroscopy from the Coude spectrograph of the Rozhen Observatory (Bulgaria) allows further information on the model and the mass transfer process. Very high resolution radio observations would also have much to reveal about astrophysics of the semi-detached configuration, not only directly, by informing about the outermost envelopes of the components, but indirectly through high accuracy positional information. We show how this may be related to careful period and astrometric studies, δ Lib thus provides a rich source of information on the astrophysics of the Algol configuration.

Radio and optical intra-day variability observations of five blazars

We carried out a pilot campaign of radio and optical band intra-day variability (IDV) observations of five blazars (3C66A, S5 0716+714, OJ287, B0925+504 and BL Lacertae) on 2015 December 18-21 by using the radio telescope in Effelsberg (Germany) and several optical telescopes in Asia, Europe and America. After calibration, the light curves from both 5 GHz radio band and the optical R band were obtained, although the data were not smoothly sampled over the sampling period of about four days. We tentatively analyse the amplitudes and time-scales of the variabilities, and any possible periodicity. The blazars vary significantly in the radio (except 3C66A and BL Lacertae with only marginal variations) and optical bands on intra-and inter-day time-scales, and the source B0925+504 exhibits a strong quasi-periodic radio variability. No significant correlation between the radio-and optical-band variability appears in the five sources, which we attribute to the radio IDV being dominated by interstellar scintillation whereas the optical variability comes from the source itself. However, the radio and optical-band variations appear to be weakly correlated in some sources and should be investigated based on well-sampled data from future observations.

The light and period changes of RT Andromedae

The nature of the long-term orbital period variation and the light level variation of RT And was studied based on all available photometric observations. The (O{C) diagram formed by all available times of eclipse minima could be either of a quasi-sinusoidal form superimposed on a parabolic form, or a long period sinusoidal form. The quasi-sinusoidal form with an amplitude of 0.002 days and a period of 65 years could be due to a cyclic magnetic activity modulation on the orbital period of the system. Applegates theory (Applegate 1992), in this case, predicts an3 kG mean subsurface magnetic eld for the primary component of the system. The parabolic form corresponds to a secular period decrease of about 3 10 9 m yr 1 caused by mass loss from the system, and the long-period sinusoidal form with an amplitude of 0.02 days and a period of 105 years corresponds to a secular period change caused by the light-time eect due to an unseen third star in the system. It was estimated that the unseen third star should be a low mass (lower than 0:6 m) and faint (5: m fainter than the system RT And) star, whose detection is almost impossible. Future data will add information on the nature of the secular (O{C) variation. Secular light level variation of the system was found to be irregular and no correlation was detected with the orbital period variation.

First photometric study of two southern eclipsing binaries IS Tel and DW Aps

The paper presents the first photometric analysis of two southern eclipsing binary stars, IS Tel and DW Aps. Their V light curves from the All Sky Automated Survey were modelled by using Wilson-Devinney method. The final models give these two Algol-like binary stars as having detached configurations. Absolute parameters of the components of the systems were also estimated.

Photometric study of two neglected beta Lyr-type binaries: V342 Her & V387 Her

In this study, SuperWASP light curves of V342 Her and V387 Her were analyzed by means of the Wilson–Devinney (W-D) code with a Monte Carlo (MC) search method for the first time. The final photometric solutions of these two systems show that while V342 Her has an over contact configuration in which both components overflows their Roche limiting lobes, V387 Her has a detached configuration. Photometric mass ratios and approximate absolute parameters of the systems are obtained.

Photometric investigation of hot exoplanets: TrES-3b and Qatar-1b

Abstract New photometric follow-up observations of transitting ‘hot Jupiters’ TrES-3b and Qatar-1b are presented. Weighted mean values of the solutions of light curves in R-filter for both planetary systems are reported and compared with the previous results. The transit light curves were analysed using the winfitter code. The physical properties of the planets were estimated. The planet radii are found to be R p = 1.381 ± 0.033 R J for TrES-3b and R p = 1.142 ± 0.025 R J for Qatar-1b. Transit times and their uncertainties were also determined and a new linear ephemeris was computed for both systems. Analysis of transit times showed that a significant signal could not be determined for TrES-3b, while weak evidence was found for Qatar-1b, which might be tested using more precise future transit times.