A. Elmasli

The Blazhko effect of RR Lyrae in 2003-2004

Aims. Extensive photometry of RR Lyr was obtained over a 421-day interval in 2003-2004, covering more than 10 Blazhko cycles in a multisite campaign. The length and density of this data set allow for a detailed analysis. Methods. We used Fourier techniques to study RR Lyrs behavior over the pulsation and the Blazhko cycle. We propose a two-frequency model for decomposing the frequency spectrum. Results. The light variations were fitted with the main radial frequency, its harmonics up to 11th order, and the detected triplet frequencies. No significant quintuplet components were found in the frequency spectrum. Given the total time span of the measurements, we can now unambiguously conclude that the Blazhko period has become notably shorter than the previously known value of 40.8 days, whereas the main pulsation period remained roughly the same. Changes in the modulation period have been reported for other well-studied Blazhko variables. They challenge the explanations for the Blazhko effect which link the modulation period directly to the rotation period. The new photometry reveals an interval in the pulsation cycle of RR Lyr during which the stars intensity barely changes over the Blazhko cycle. This interval occurs during the infalling motion and between the supposed phases of the early and the main shock. The data also permit a more detailed study of the light curve shape at different phases in the Blazhko period through Fourier parameters.

An in-depth spectroscopic analysis of RR Lyr Variations over the pulsation cycle

The stellar parameters of RR Lyrae stars vary considerably over a pulsation cycle, and their determination is crucial for stellar modelling. We present a detailed spectroscopic analysis of the pulsating star RR Lyr, the prototype of its class, over a complete pulsation cycle, based on high-resolution spectra collected at the 2.7-m telescope of McDonald Observatory. We used simultaneous photometry to determine the accurate pulsation phase of each spectrum and determined the effective temperature, the shape of the depth-dependent microturbulent velocity, and the abundance of several elements, for each phase. The surface gravity was fixed to 2.4. Element abundances resulting from our analysis are stable over the pulsation cycle. However, a variation in ionization equilibrium is observed around minimum radius. We attribute this mostly to a dynamical acceleration contributing to the surface gravity. Variable turbulent convection on time-scales longer than the pulsation cycle has been proposed as a cause for the Blazhko effect. We test this hypothesis to some extent by using the derived variable depth-dependent microturbulent velocity profiles to estimate their effect on the stellar magnitude. These effects turn out to be wavelength dependent and much smaller than the observed light variations over the Blazhko cycle: if variations in the turbulent motions are entirely responsible for the Blazhko effect, they must surpass the scales covered by the microturbulent velocity. This work demonstrates the possibility of a self-consistent spectroscopic analysis over an entire pulsation cycle using static atmosphere models, provided one takes into account certain features of a rapidly pulsating atmosphere.

Physical parameters of some close binaries: ET Boo, V1123 Tau, V1191 Cyg, V1073 Cyg and V357 Peg

Abstract With the aim of providing new and up-to-date absolute parameters of some close binary systems, new BVR CCD photometry was carried out at the Ankara University Observatory ( AUG) for five eclipsing binaries, ET Boo, V1123 Tau, V1191 Cyg, V1073 Cyg and V357 Peg between April, 2007 and October, 2008. In this paper, we present the orbital solutions for these systems obtained by simultaneous light and radial velocity curve analyses. Extensive orbital solution and absolute parameters for ET Boo system were given for the first time through this study. According to the analyses, ET Boo is a detached binary while the parameters of four remaining systems are consistent with the nature of contact binaries. The evolutionary status of the components of these systems are also discussed by referring to their absolute parameters found in this study.

A spectroscopic study of DD UMa: Ursa Major group member and candidate for BRITE

The Ursa Major group is a nearby stellar supercluster which, while not gravitationally bound, is defined by co-moving mem bers. DD UMa is aScuti star whose membership in the Ursa Major group is unclear. The objective of this study is to confirm the membership of DD U Ma in the Ursa Major group, as well as perform a detailed spectral analysis of the star. Since DD UMa is a low-amplitudeScuti star, we performed a frequency analysis. We determined fundamental parameters, chemical abundances, and derive a mass and age for the star. For this study we observed DD UMa at the Okayama Astrophysical Observatory with the high-resolution spectrograph HIDES, between the 27 th of February and the 4 th March, 2009. Additional observations were extracted from the ELODIE archive in order to expand our abundance analysis. Group membership of DD UMa was assessed by examining the velocity of the star in Galactic coordinates. Pulsational frequencies were det ermined by examining line profile variability in the HIDES sp ectra. Stellar fundamental parameters and chemical abundances were derived by fitting synthetic spectra to both the HIDES and E LODIE observations. DD UMa is found to be a member of the extended stream of the Ursa Major group, based on the space motion of the star. This is supported by the chemical abundances of the star being consistent with those of Ursa Major group members. The star is found to be chemically solar, with Te f f = 7450± 150 K and log g = 3.98± 0.2. We found pulsational frequencies of 9.4 c/d and 15.0 c/d. While these frequencies are insuffi cient to perform an asteroseismic study, DD UMa is a good bright star candidate for future study by the BRITE-constellation.

The Period Analysis of the Hierarchical System DI Peg

The existence of an additional body around a binary system can be detected by the help of the light-travel time effect. Due to the motions of binary and the companion stars around the common mass center of the ternary system, the light-time effect produces an irregularity on the eclipse timings. Monitoring the variations in these timings, sub-stellar or planet companions orbiting around the binary system can be identified. In this paper, additional bodies orbiting the Algol type binary DI Peg are examined by using the archival eclipse timings including our CCD data observed at the Ankara University Kreiken Observatory. More than five hundred minimum times equivalent to around nine decades are employed to identify the orbital behavior of the binary system. The best fit to the timings shows that the orbital period of DI Peg has variation due to an integration of two sinusoids with the periods of

Chemical abundance analysis of π Dra and HR 7545

P_3 = 49.50\pm0.36

A DETAILED SPECTROPOLARIMETRIC ANALYSIS OF THE PLANET-HOSTING STAR WASP-12* , **

yr and

The accuracy of stellar atmospheric parameter determinations: a case study with HD 32115 and HD 37594

P_4 = 27.40\pm0.24

Detection of a magnetic field in three old and inactive solar-like planet-hosting stars

yr. The orbital change is thought to be most likely due to the existence of two M-type red dwarf companions with the masses of

Chemical abundance analysis of the A-type stars CP Cyg and HD 33266

M_3 =0.213 \pm 0.021