A study of a spot migration in two contact binaries : KIC 2159783 and KIC 6118779

Data of contact binaries, provided by the Kepler spacecraft, can be successfully applied to estimate the parameters of a binary system only if its light curve has a flat-bottom secondary minimum. The derived system parameters are accurate enough to search for a spot migration using the Wilson-Devinney code. For binaries with a regular activity (e.g. KIC 6118779) the numerical spot modeling is consistent with a model-independent light curve morphology analysis. Finally, we proved that spot migration cycles established by the Wilson-Devinney modeling correspond to the O'Connell effect and maxima separation methods

A planet orbiting an sdB star and an M dwarf in 2M 1938+4603

We present a preliminary analysis of the 2M 1938+4603 star. It is an eclipsing binary system consisting of a primary sdB component and a secondary M dwarf. The photometric data are dominated by mutual eclipses and a very strong reflection effect. The primary has a fairly rich pulsation spectrum which can be used to study its interior. On the other hand, the pulsations affect the binary trend and vice versa what makes the analysis very difficult. Therefore, we attempted at proper modeling of the light variation due to eclipses and reflection and their removal from the data so it does not affect the Fourier analysis of stellar pulsations. We focus on mid-times of over 16 000 primary and secondary minima, which were used to verify stability of the orbital period. The O-C diagram indicates possible parabolic and sinusoidal variations, commonly explained by period changes caused by evolution and a presence of a third body, respectively

Modelling of the semi-detached binary star WZ Corvi

We present results from modeling of multicolor light curves of the semi-detached, algol- type binary system WZ Corvi. We analyzed V R data gathered in 2010 and new BV R_{c}I_{c} observations collected in 2012. Two models for WZ Crv are considered: the first was derived under the assumption that the temperature of the primary component, having the dominant contribution to total system light, corresponds to spectral type F7, and the second model, in which the temperature of the secondary was estimated from the colors observed at the at bottom of the primary minimum. The new set of observations shows almost no difference in maxima heights, obvious in the earlier, 2010 data. However, primary minimum in V and R is deeper than in the 2010 light curve. We explain the variable shape of the system light curve as spot(s) present on primary or secondary component(s) due to their magnetic activity. Based on the derived solutions, we calculate relative physical (assuming the primary component to be a Main Sequence star) parameters of WZ Crv for both models

Time-domain behavior of blazar OJ 287 and the binary supermassive black hole conjecture

The proper understanding of blazar variability at the various electromagnetic spectral bands is one goal of multifrequency astrophysics. In this frame a peculiar and controversial phenomenology is the periodicity, postulated for long-term radio or optical flux light curves of about a dozen of blazars. The well-known BL Lac object OJ 287 (PKS 0851+202, S3 0851+20, PG 0851+202, z = 0.306) is not only a high-variable, peculiar, extragalactic source with hints for approximatively cyclical optical outbursts, but it also represents a case of substantial intensive and extensive (longterm) multifrequency observations. This rich database allow us a deeper analysis based on a wide range of variability timescales with some recent results that are highlighted here

Detection of a planet in the sdB + M dwarf binary system 2M 1938+4603

We analyze 37 months of Kepler photometry of 2M 1938+4603, a binary system with a pulsating hot subdwarf primary and an M-dwarf companion that shows strong reflection effect. We measured the eclipse timings from more than 16 000 primary and secondary eclipses and discovered a periodic variation in the timing signal that we ascribe to a third body in the system. We also discovered a significant long-term trend that may be an evolutionary effect or a hint of more bodies. Upon the assumption that the third body is orbiting in the same plane as the primary, we establish that it must be a Jupiter-mass object orbiting with a period of 416 days at a distance of 0.92 AU. This mass is the lowest among all tertiary components detected in similar systems

Period changes of the sample of eclipsing binaries with active chromospheres

In this work we present results derived from analysis of the O-C behaviour of ten eclipsing binary systems: AR Lac, CG Cyg, HP Aur, MM Her, RS CVn, RT And, SV Cam, V471 Tau, WW Dra and CF Tuc. It was proved on the basis of moments of minima compiled from the literature and new ones determined from recent observations, that these binaries show long term (19-91 years) modulations of their orbital periods, clearly visible in their O-C diagrams. Two possible explanations for this effect are considered: (1) the light-travel time effect due to the presence of a third body orbiting the eclipsing systems; (2) the Applegate mechanism predicting period modulation by changes in the distribution of angular momentum as a star goes through its activity cycles. It was found that in the case of four systems the existence of a third star, orbiting the binary, is a more plausible explanation of observations

Multiwavelength variability of the radio quasar J2042+7508

In this paper, we present our results of study on the long term multiwavelength variability properties of the quasar J2042+7508 (4C +74.26) – a giant radio source located at the redshift of 0.104. This source exhibits interesting emission and structural properties when observed in various wavelengths, including X-ray, optical and radio frequencies. Therefore, exploring these properties through multifrequency variability studies presents a great importance to our understanding of the evolution of quasars and radio-loud unification schemes. We found a trend of anticorrelation with time lag of about three months between optical and radio light curves. A weak correlation with a longer time lag of about 230 days might also exist. Using the structure function method, applied to our six years long, optical data, we arrived at a conclusion that the quasar variability with amplitude of about 0.3 magnitude, is likely caused by an accretion disk instability