M. Yılmaz

PHOTOMETRIC ANALYSIS OF OVERCONTACT BINARIES AK HER, HI DRA, V1128 TAU, AND V2612 OPH

We analyze new, high quality multicolor light curves of four overcontact binaries: AK Her, HI Dra, V1128 Tau, and V2612 Oph, and determine their orbital and physical parameters using the modeling program of G. Djurasevic and recently published results of radial velocity studies. The achieved precision in absolute masses is between 10% and 20%, and the precision in absolute radii is between 5% and 10%. All four systems are W UMa-type binaries with bright or dark spots indicative of mass and energy transfer or surface activity. We estimate the distances and the ages of the systems using the luminosities computed through our analysis, and perform an O – C study for V1128 Tau, which reveals a complex period variation that can be interpreted in terms of mass loss/exchange and either the presence of the third body, or the magnetic activity on one of the components. We conclude that further observations of these systems are needed to deepen our understanding of their nature and variability.

Recurrent star-spot activity and differential rotation in KIC 11560447

We present a detailed analysis of surface inhomogeneities on the K1-type sub-giant component of the rapidly rotating eclipsing binary KIC 11560447, using high-precision Kepler light curves spanning nearly four years, corresponding to about 2800 orbital revolutions. We precisely determine the system parameters using high-resolution spectra from the 2.1-m Otto Struve Telescope at the McDonald Observatory. We apply the maximum entropy method to reconstruct the relative longitudinal spot occupancy. Our numerical tests show that the procedure can recover large-scale random distributions of individually unresolved spots, and can track the phase migration of up to three major spot clusters. By determining the drift rates of various spotted regions in orbital longitude, we suggest a way to constrain surface differential rotation and show that the results are consistent with periodograms. The K1IV star exhibits two mildly preferred longitudes of emergence, indications of solar-like differential rotation, and a 0.5 to 1.3-year recurrence period in starspot emergence, accompanied by a secular increase in the axisymmetric component of spot occupancy.

PHOTOMETRIC, SPECTROSCOPIC, AND ORBITAL PERIOD STUDY OF THREE EARLY-TYPE SEMI-DETACHED SYSTEMS: XZ AQL, UX HER, AND AT PEG

In this paper we present a combined photometric, spectroscopic and orbital period study of three early-type eclipsing binary systems: XZ Aql, UX Her, and AT Peg. As a result, we have derived the absolute parameters of their components and, on that basis, we discuss their evolutionary states. Furthermore, we compare their parameters with those of other binary systems and with the theoretical models. An analysis of all available up-to-date times of minima indicated that all three systems studied here show cyclic orbital changes, their origin is discussed in detail. Finally, we performed a frequency analysis for possible pulsational behavior and as a result we suggest that XZ Aql hosts a {delta} Scuti component.

The absolute parameters of the detached eclipsing binary V482 Per

Abstract We present the results of a spectroscopic, photometric and orbital period variation analysis of the detached eclipsing binary V482xa0Per. We derived the absolute parameters of the system (M1 = 1.51 M⊙, M2 = 1.29 M⊙, R1 = 2.39 R⊙, R2 = 1.45 R⊙, L1 = 10.15 L⊙, L2 = 3.01 L⊙) for the first time in literature, based on an analysis of our own photometric and spectroscopic observations. We confirm the nature of the variations observed in the system’s orbital period, suggested to be periodic by earlier works. A light time effect due to a physically bound, star-sized companion (M3 = 2.14 M⊙) on a highly eccentric (e = 0.83) orbit, seems to be the most likely cause. We argue that the companion can not be a single star but another binary instead. We calculated the evolutionary states of the system’s components, and we found that the primary is slightly evolving after the main sequence, while the less massive secondary lies well inside it.

A Jupiter-mass planet around the K0 giant HD 208897

For over 10 years, we have carried out a precise radial velocity (RV) survey to find substellar companions around evolved G,K-type stars to extend our knowledge of planet formation and evolution. We performed high precision RV measurements for the giant star HD 208897 using an iodine (I2) absorption cell. The measurements were made at TUB.ITAK National Observatory (TUG, RTT150) and Okayama Astrophysical Observatory (OAO). For the origin of the periodic variation seen in the RV data of the star, we adopted a Keplerian motion caused by an unseen companion. We found that the star hosts a planet with a minimum mass of m2sini=1.40MJ, which is relatively low compared to those of known planets orbiting evolved intermediate-mass stars. The planet is in a nearly circular orbit with a period of P=353 days at about 1 AU distance from the host star. The star is metal rich and located at the early phase of ascent along the red giant branch. The photometric observations of the star at Ankara University Kreiken Observatory (AUKR) and the HIPPARCOS photometry show no sign of variation with periods associated with the RV variation. Neither bisector velocity analysis nor analysis of the Ca II and Halpha lines shows any correlation with the RV measurements.

A Tale on Two Close Binaries in Pegasus

Abstract We present the simultaneous light and radial velocity curve analysis of two contact binaries in Pegasus using the Wilson-Devinney code. The following absolute astrophysical parameters are determined: masses, radii and effective temperatures. BB Peg is a W-subtype W UMa-type binary, components of which are main sequence stars with 0.50 M⊙ and 1.40 M⊙. The radii of its components are R1 = 0.81 R⊙ and R2 = 1.28 R⊙. V407 Peg is an A-subtype contact binary composed of two subgiant components with masses 1.70 M⊙ and 0.43 M⊙, and radii R1 = 2.17 R⊙ and R2 = 1.25 R⊙. Comparisons with the theoretical models for solar composition by Girardi et al. (2000) confirms our classification and supports the results.