S. O. Selam

Medium-resolution Isaac Newton Telescope library of empirical spectra

A new stellar library developed for stellar population synt hesis modeling is presented. The library consist of 985 stars spanning a large range in atmosphe ric parameters. The spectra were obtained at the 2.5m INT telescope and cover the range λλ 3525–7500̊A at 2.3Å (FWHM) spectral resolution. The spectral resolution, spectral ty pe coverage, flux calibration accuracy and number of stars represent a substantial improvement ove r previous libraries used in population synthesis models.

Medium-resolution Isaac Newton Telescope library of empirical spectra - II. The stellar atmospheric parameters

We present a homogeneous set of stellar atmospheric parameters (T-eff, log g, [Fe/H]) for MILES, a new spectral stellar library covering the range lambda lambda 3525-7500 angstrom at 2.3 angstrom (FWHM) spectral resolution. The library consists of 985 stars spanning a large range in atmospheric parameters, from super-metal-rich, cool stars to hot, metal-poor stars. The spectral resolution, spectral type coverage and number of stars represent a substantial improvement over previous libraries used in population synthesis models. The atmospheric parameters that we present here are the result of a previous, extensive compilation from the literature. In order to construct a homogeneous data set of atmospheric parameters we have taken the sample of stars of Soubiran, Katz & Cayrel, which has very well determined fundamental parameters, as the standard reference system for our field stars, and have calibrated and bootstrapped the data from other papers against it. The atmospheric parameters for our cluster stars have also been revised and updated according to recent metallicity scales, colour-temperature relations and improved set of isochrones.

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.

Key parameters of W UMa-type contact binaries discovered by HIPPARCOS

A sample of W UMa-type binaries which were discovered by the HIPPARCOS satellite was constructed with the aid of well defined selection criteria described in this work. The selection process showed up that several systems of which the variability types have been assigned as EB in HIPPARCOS catalogue are genuine contact binaries of W UMa-type. The light curves of the 64 selected systems based on HIPPARCOS photometry were analyzed with the aid of light curve synthesis method by Rucinski and their geometric elements (namely mass ratio q, degree of contact f , and orbital inclination i) were determined. The solutions were obtained for the first time for many of the systems in the sample and would be a good source for their future light curve analyses based on more precise follow-up observations.

Bisectors of the HARPS cross-correlation function - The dependence on stellar atmospheric parameters

Context. Bisectors of the HARPS cross-correlation function (CCF) can discern between planetary radial-velocity (RV) signals and spurious RV signals from stellar magnetic activity variations. However, little is known about the effects of the stellar atmosphere on CCF bisectors or how these effects vary with spectral type and luminosity class. Aims. Here we investigate the variations in the shapes of HARPS CCF bisectors across the HR diagram in order to relate these to the basic stellar parameters, surface gravity and temperature. Methods. We use archive spectra of 67 well studied stars observed with HARPS and extract mean CCF bisectors. We derive previously defined bisector measures (BIS, vbot, cb) and we define and derive a new measure called the CCF bisector span (CBS) from the minimum radius of curvature on direct fits to the CCF bisector. Results. We show that the bisector measures correlate differently, and non-linearly with log g and Teff. The resulting correlations allow for the estimation of log g and Teff from the bisector measures. We compare our results with 3D stellar atmosphere models and show that we can reproduce the shape of the CCF bisector for the Sun.

A Photometric Study of the Contact Binaries: XY Leo, EE Cet and AQ Psc

New photoelectric BV light curves of three close eclipsing binaries XY Leo, EE Cet and AQ Psc were observed and studied with the aim to derive the physical parameters of these systems. The following results were obtained: (a) the W-type contact binary system XY Leo is in a marginal overcontact configuration (fover ∼ 2.4%) with a relatively large temperature difference between the components (∼330 K); (b) due to the proximity of the companion of EE Cet in the visual binary ADS 2163, the light curves of EE Cet were contaminated by the third light, having a relatively large impact on the system-parameter estimates, and the solutions made with the third light parameter, L3 ∼ 0.54, describe EE Cet as a high-overcontact (fover ∼ 33%) W-type system; (c) the A-type W UMa contact eclipsing binary AQ Psc is in an overcontact configuration (fover ∼ 20%). The relatively small temperature difference (∼150 K) and large difference in component masses suggest a significant energy transfer through the connecting neck of the common envelope. The absolute system parameters are obtained by combining our photometric solution with the spectroscopic elements given by other authors.

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.

Preliminary results of the alignment and Hartmann tests of the AZT-22 telescope

The AZT-22 telescope installed in Turkey (Antalia) was aligned and tested on stars by the Hartmann method. The rms normal deviation of an equivalent optical system is 0.040±0.016 µm. The circle of confusion is 0.40±0.04 arcsec in diameter at a 50% energy level.

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.