Cafer Ibanoglu

Active close binaries

Since the 1970s symposia or colloquia devoted to recent research on close binaries have been held around the world almost annually. At meetings of the General Assembly of the International Astronomical Union this topic has also been discussed in detail at presentations in various commission meetings and also as invited talks by leading astronomers in the field. In recent years, fundamental changes have taken place in the study of close binaries due to the improvements in observational techniques, extension of observations from X-ray to radio regions of the electromagnetic spectrum, and advances in theoretical studies. For more than a decade, a group of astronomers at Ege University Observatory has been concentrating on active close binaries with particular emphasis on the behaviour of the light curves of chromospherically active systems. Thus, we decided to organize an international meeting in Western Anatolia, where this part of Turkey had been the cradle for great developments in science during antiquity. KUljadasi, located only minutes away from Ephesus, one of the seven wonders of the world, was selected to be the meeting site. Close binary systems constitute a very rich source of information about the physical properties of the component stars. Some systems are eclipsing variables, where periodic recurrences of eclipses are observed as comparatively brief decreases in the total brightness of the binary system. Precise methods of photometric observations make it possible to obtain the light variations of these systems because of eclipses and other phenomena.

Variable stars as essential astrophysical tools

Preface C. Ibanogammalu. Scientific Organizing Committee. Conference Photograph. List of Participants. I. Basic Aspects of Stellar Structure and Pulsation J. Christensen-Dalsgaard, W.A. Dziembowski. II. An Introduction to Helioseismology J. Christensen-Dalsgaard, et al. Solar Models and Helioseismology M. Yildiz. III. Astrophysical Equation of State and Opacity W. Dappen, J.A. Guzik. IV. Introduction to Asteroseismology of delta Scuti Stars J.A. Guzik. The Pulsational Behaviour of Variable Stars in The Lower Part of the Instability Strip E. Poretti. 57 Tau, a delta Scuti Star in Binary System in the Hyades M. Paparo, E. Rodriguez, Z. Kollath. V. Evolution and Hydrodynamics of Rotating Stars R.G. Deupree, J.A. Guzik. VI. Techniques of Collection, Reduction and Analysis of Data of Pulsating Stars I: Multi-Band Multi-Longitude Campaigns F.M. Zerbi. Techniques of Collection, Reduction and Analysis of Data of Pulsating Stars II: Cluster Surveys, Multi-Band Observations, New Approaches for gamma Doradus and delta Scuti Stars F.M. Zerbi. Simultaneous Light Curve, Color Curve and Line Profile Fitting for Pulsating Stars. Objects in lower part of Cepheid Instability Strip: delta Scuti and gamma Doradus Stars F.M. Zerbi. VII. An Introduction to Ap Stars, roAp Stars and the Asteroseismology of roAp Stars D.W. Kurtz. Evidence for, and Development of, the Oblique Pulsator Model D.W. Kurtz. Long-term Monitoring of Cyclic Frequency Variability in roAp Stars D.W. Kurtz. Multi-color Observations and Atmospheric Level Effects in roAp Stars D.W. Kurtz. Asteroseismology Versus Astrometry. Testing p-mode Predictions for roAp stars againstHipparcos J. Matthews. Pulsational Radial Velocity Studies of roAp Stars g Equulei, 33 Librae, H.D. 134214, HR 1217, and HD 122970 A.P. Hatzes, et al. Asteroseismology with a Spatial Resolution: Prospects for Rapid RV-Spectroscopy of roAp Stars D.E. Mkrtichian, et al. VIII. Asteroseismology of Cepheids E. Poretti. On the Normalization of Cepheid Period-Luminosity Relationships I. Iben, Jr. IX. Theoretical Models of g Doradus Variables A.B. Kaye, et al. Gamma Doradus Stars: Observational Constraints to Theoretical Models F.M. Zerbi, A.B. Kaye. X. Trend Analysis of Long Period Variables J.A. Mattei, G. Foster. Absolute magnitudes of M Type Semi-regular Variables in Hipparcos Catalogue Z. Aslan, C. Yesilyaprak. XI. Pulsating White Dwarf Stars S.D. Kawaler. XII. The O--C Diagram C. Sterken. Period Changes as a Tool to Study Stellar Evolution G. Handler. XIII. Binary Stars. Apisidal Motion in Close Binaries C. Ibanoglu. Apsidal Motion Studies for DI Her M. Yldiz, et al. Irradiation Effects and Light Curve Solution of Close Hot Binaries H. Drechsel. Orbital Period Variations of Some Algol-Type Binaries S.O. Selam, O. Demircan. Period Changes as a Tool to Study Unseen Components Around Eclipsing Binaries O. Demircan. Asymmetry in the Light Curves of Massive Binaries O. Demircan. On the Gravity Darkening of Eclipsing Variables of W UMa Type P.G. Niarchos. UBP Photometry of the Massive Eclipsing Binary TT Aurigae S. Ozdemir, et al. Orbital Period Changes and Global Evolution of Contact Binaries H. Rovithis-Livaniou, A. Kalimeris. Det

Spin angular momentum evolution of the long-period Algols

We consider the spin angular momentum evolution of the accreting components of Algol-type binary stars. In wider Algols the accretion is through a disc so that the accreted material can transfer enough angular momentum to the gainer that material at its equator should be spinning at breakup. We demonstrate that even a small amount of mass transfer, much less than required to produce today’s mass ratios, transfers enough angular momentum to spin the gainer up to this critical rotation velocity. However the accretors in these systems have spins typically between 10 and 40 per cent of the critical rate. So some mechanism for angular momentum loss from the gainers is required. Unlike solar-type chromospherically active stars, with enhanced magnetic activity which leads to angular momentum and mass loss, the gainers in classical Algols have radiative envelopes. We further find that normal radiative tides are far too weak to account for the necessary angular momentum loss. Thus enhanced mass loss in a stellar wind seems to be required to spin-down the gainers in classical Algol systems. We consider generation of magnetic fields in the radiative atmospheres in a differentially rotating star and the possibility of angular momentum loss driven by strong stellar winds in the intermediate-mass stars, such as the primaries of the Algols. Differential rotation, induced by the accretion itself, may produce such winds which carry away enough angular momentum to reduce their rotational velocities to the today’s observed values. We apply this model to

New light curve analysis and period changes of the overcontact binary XY Leonis

Light curves and photometric solutions of the contact binary XY Leo are presented. The UB VRlight curves appear to be almost symmetric. The B and V light curves were analysed with the Wilson-Devinney code and the orbital parameters of the system were obtained and compared with those obtained in previous studies. All the times of minimum light were collected and combined with the new ones obtained in this study. The orbital period of the system oscillates with a period of 19:6 years and a semi-amplitude of 0:023 day. This regular change was analysed under the assumption of the third body hypothesis. The time delay and advance due to the orbit of the eclipsing pair around the third component were computed and subtracted from the original residuals obtained with the linear light elements. The remaining residuals also show a parabolic change. Therefore, we assumed that the orbital period of the system changes with time due to at least two dierent causes. The parabolic change of the period may be attributed to either mass transfer from less massive component to the more massive one, or an additional component bounded to the double binary system with a longer period.

T-Cyg1-12664: a low-mass chromospherically active eclipsing binary in the Kepler field

The eclipsing binary T-Cyg1-12664 has been observed both spectroscopically and photo- metrically, and the radial velocities of both the components and the ground-based VRI light curves have been obtained. The Kepler R data and radial velocities for the system have been analysed simultaneously. Masses and radii have been obtained as 0.680 ± 0.021 Mand 0.613 ± 0.007 Rfor the primary star and 0.341 ± 0.012 Mand 0.897 ± 0.012 Rfor the secondary star. The distance to the system has been estimated as 127 ± 14 pc. The ob- served wave-like distortion at out-of-eclipse is modelled with two separate spots on the more massive star, which is also confirmed by the Ca II K and H emission lines in its spectra. The locations of the components in the mass-radius and mass-effective temperature planes have been compared with the well-determined low-mass components of eclipsing binaries as well as with the theoretical models. While the radius of the primary star is consistent with the main-sequence stars, the radius of the less massive component appears to be 2.8 times larger than that of the main-sequence models. A comparison of the radii of low-mass stars with the models reveals that the observationally determined radii begin to deviate from the models with a mass of 0.27 M� , and suddenly reach to maximum deviation at a mass of 0.34 M� . Then, the deviations begin to decrease up to the solar mass. The maximum deviation, seen at a mass of about 0.34 M� , is very close to the mass of fully convective stars, as suggested by theoretical studies. A third star in the direction of the eclipsing pair has been detected from our VRI images. The observed infrared excess of the binary most probably arises from this star, which can be radiated mostly in the infrared bands.

The multiperiodicity of the γ Doradus stars HD 224945 and HD 224638 as detected from a multisite campaign

We discuss new photometric data collected on the Dor variables HD 224945 and HD 224638. Multiperiodicity was detected in both stars, thanks to the clear spectral window of a multisite campaign that involved ve observatories. HD 224945 shows the shortest period among the Dor stars, i.e., 0.3330 d. The pulsation behaviour is very dierent: HD 224945 displays a set of frequencies spread over an interval much larger than that of HD 224638. We clearly found evidence for amplitude variations in the excited modes by comparing data from dierent years. HD 224945 and HD 224638 are among the best examples of Dor stars that show multimode pulsations, which make them very interesting from an asteroseismological point of view.

Period variation and the new light curves of V471 Tauri

The light curve and period variation of the eclipsing system V471 Tau is discussed. The migration period of 191 days obtained recently by Ibanoğlu agrees well with the new observations. The period decreases by about one second per century, which may correspond to a mass transfer of 1×10−7 solar mass. Furthermore, the O−C diagram shows a noticeable sine curve super-imposed on the parabolic variation. The period of the sine curve is about 3.1 years.

MY Serpentis: a high-mass triple system in the Ser OB2 association

We present spectroscopic observations of the massive multiple system HD\,167971, located in the open cluster NGC\,6604. The brighter component of the triple system is the overcontact eclipsing binary MY\,Ser with an orbital period of 3.32\,days. The radial velocities and the previously published UBV data obtained by \citet{may10} and the UBVRI light curves by \citet{dav88} are analysed for the physical properties of the components. We determine the following absolute parameters: for the primary star M

Orbital Period Changes of Algol-type Binaries: S Equulei and AB Cassiopeiae

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Two-colour photoelectric investigation of AR Lacertae

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