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Öğe THE ABSOLUTE PARAMETERS FOR NSVS 11868841 AND THE OVERSIZED STARS IN LOW-MASS ECLIPSING BINARIES(Univ Nacional Autonoma Mexico, Inst De Astronomia, 2010) Cakirli, O.; Ibanoglu, C.; Dervisoglu, A.Spectroscopic observations of the low-mass eclipsing binary NSVS 11868841 have been obtained and the radial velocities were derived for both components. The masses and radii determined for the components are M(1) = 0.870 +/- 0.074 M(circle dot), M(2) = 0.607 +/- 0.053 M(circle dot) and R(1) = 0.983 +/- 0.030 R(circle dot) R(2) = 0.901 +/- 0.026 R(circle dot). Both the primary and secondary stars' radii are 10% and 57% larger than those of zeroage-main-sequence stars with the same masses. This discrepancy may arise from the large spot coverage of both stars. We collected absolute parameters of 21 low mass double-lined eclipsing binaries arid compared their positions in the mass-radius and mass-effective temperature panels. The large radii and lower effective temperatures found for NSV 11868841 are solved neither with differences in metallicity nor in mixing length parameters. These discrepancies for low mass stars may be due to magnetic fields inhibiting the convective energy transport, which lead to a large magnetic spot coverage of the surface of such low mass stars.Öğe Absolute parameters of the eclipsing binary V821 Cas from UBVRI light curves and radial velocities(Wiley-Blackwell Publishing, Inc, 2009) Cakirli, Oe; Ibanoglu, C.; Bilir, S.; Sipahi, E.We present UBVRI photometric measurements and spectroscopic observations of the double-lined eclipsing binary V821 Cas. The radial velocities were obtained by means of the cross-correlation technique. Simultaneous analyses of the multiband light curves and RVs give the absolute parameters for the stars as: M(1) = 2.05 +/- 0.07M(circle dot); M(2) = 1.63 +/- 0.06M(circle dot); R(1) = 2.31 +/- 0.03R(circle dot); R(2) = 1.39 +/- 0.02R(circle dot); T(eff1) = 9400 +/- 400 K and T(eff2) = 8 600 +/- 400 K. An analysis of the O-C residuals yielded an apsidal motion in the binary at a rate of omega = 0 degrees.0149 +/- 0 degrees.0023 cycle(-1), corresponding to an apsidal period of U = 118 +/- 19 yr. Subtracting the relativistic contribution, we find that log k(2obs) = -2.590 which is in agreement with the value predicted by theoretical models. Comparison with current stellar evolution models gives an age of 5.6 x 10(8) yr for the system.Öğe An algol type binary with a delta Scuti component: RZ Cassiopeiae revisited(Wiley-V C H Verlag Gmbh, 2006) Soydugan, E.; Soydugan, F.; Ibanoglu, C.; Frasca, A.; Demircan, O.; Akan, M. C.We present new BV photometry and spectroscopic observations of RZ Cassiopeiae. The light and radial velocity curves were formed by the new observations which have been analyzed simultaneously by using the Wilson-Dewinney code. The non-synchronous rotational velocity v(1) sin i = 76 +/- 6 km s(-1), deduced for the primary component from the new spectroscopic observations, was also incorporated in the analysis. A time-series analysis of the residual light curves revealed the multi-periodic pulsations of the primary component of RZ Cas. The main peak in the frequency spectrum was observed at about 64.197 c d(-1) in both B and V bands. The pulsational constant was calculated to be 0.0116 days. This value corresponds to high overtones (n similar to 6) of non-radial mode oscillations. We find significant changes in the pulsational amplitude of the primary component from year to year. The peak-to-peak pulsational amplitude of the main frequency displays a decrease from 0.(m)-013 in 2000 to 0.(m)002 in 2001 and thereafter we have found an increase again in the amplitude to 0.(m)01 in the year 2002. We propose the mass transfer from the cool secondary to the pulsating primary as a possible explanation for such remarkable changes in the pulsational behavior of the primary component. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.Öğe Analysis of the massive eclipsing binary V1441 Aql(Elsevier, 2015) Cakirli, O.; Ibanoglu, C.; Sipahi, E.; Frasca, A.; Catanzaro, G.We present new spectroscopic observations of the early type, double-lined eclipsing binary V1441 Aql. The radial velocities and the available photometric data obtained by ASAS is analysed for deriving the parameters of the components. The components of V1441 Aql are shown to be a B3 IV primary with a mass M-p = 8.02 +/- 0.51 M-circle dot and radius R-p = 7.33 +/- 0.19 R-circle dot and a B9 III secondary with a mass = 1.92 +/- 0.14 M-circle dot and radius R-s = 4.22 +/- 0.11 R-circle dot. Our analyses show that V1441 Aql is a doublecontact system with rapidly rotating components. Based on the position of the components plotted on the theoretical Hertzsprung-Russell diagram, we estimate that the ages of V1441 Aql is about 30 Myr, neglecting the effects of mass exchange between the components. Using the UBVJHK magnitudes and interstellar absorption we estimated the mean distance to the system V1441 Aql as 550 +/- 25 pc. (C) 2014 Elsevier B.V. All rights reserved.Öğe Angular momentum evolution of Algol binaries(Oxford Univ Press, 2006) Ibanoglu, C.; Soydugan, F.; Soydugan, E.; Dervisoglu, A.We have compiled the well-determined absolute parameters of Algol-type binaries. The lists contain the parameters of 74 detached and 61 semidetached close binaries. The double-lined eclipsing binaries provide not only the most accurate determinations of stellar mass, radius and temperatures but also distance-independent luminosity for each of their individual components. The distributions of the primary and secondary masses of detached binaries (DBs) are similar, whilst the secondary masses of the semidetached binaries (SDBs) are mostly smaller than 2 M-circle dot with a peak in the M-2-bin (0.21-1.0). The components of the DBs are almost all located in the main-sequence band. On the contrary, the secondary components of the SDBs have larger radii and luminosity with respect to the same mass and the same effective temperature of main-sequence counterparts. They occupy a region of the Hertzsprung-Russell diagram between terminal-age main sequence and giants. Moreover, the total angular momenta and specific angular momenta are larger for the SDBs of orbital periods with P > 5 d than those of the shorter period ones. The specific angular momenta of SDBs with periods longer than 5 d are 65 per cent greater than that of the short period group with the same mass. The DBs and the SDBs with orbital periods longer and shorter than 5 d are separated into three groups in the J/M-5/3 - q diagram. The SDBs with mass ratios greater than 0.3 and P > 5 d have almost the same angular momentum to those of DBs. However, the SDBs with short periods have the smallest angular momentum even though they have the same mass ratios. This result reveals that angular momentum loss (AML) considerably affects the evolution of close binary systems. Recently, Chen, Li & Qian suggested that, in addition to magnetic braking, a circumbinary disc may play an important role in AML from Algol-type binaries. Their calculations indicated that the evolution of Algol-type binaries can be significantly affected by the circumbinary disc. Our results show that the evolution of close binaries begins as a DB and losing angular momentum, first via stellar wind and then magnetic braking plus circumbinary disc the period is shortened and orbit shrinks. Thereafter, the evolution of the system is accelerated and mass transfer rates are enhanced which result in a smaller mass ratios.Öğe Öğe Carbon deficiencies in the primaries of some classical Algols(Wiley-Blackwell, 2012) Ibanoglu, C.; Dervisoglu, A.; Cakirli, O.; Sipahi, E.; Yuce, K.The equivalent widths (EWs) of the C ii lambda 4267 angstrom line were measured for the mass-gaining primary stars of 18 Algol-type binary systems. The EWs of the gainers were compared with the EWs of single standard stars that have the same effective temperature and luminosity class. This comparison clearly indicates that the EWs of the gainers are systematically smaller than those of the standard stars. The primary components of the classical Algols, located in the main-sequence band of the HertzsprungRussell diagram, appear to be carbon-poor stars. We estimate [NC/Ntot] relative to the Sun as -1.91 for GT Cep, -1.88 for AU Mon and -1.41 for TU Mon, indicating poorer carbon abundance. An average differential carbon abundance has been estimated to be -0.82 dex relative to the Sun and -0.54 dex relative to the main-sequence standard stars. This result is taken to be an indication of material transferring from the evolved less-massive secondary components to the gainers, such that the CNO cycle processed material changed the original abundance of the gainers. There appear to be relationships between the EWs of the C ii?4267 angstrom line and the rates of orbital period increase and mass transfer in some Algols. As the mass transfer rate increases, the EW of the C ii line decreases. This indicates that accreted material has not yet been completely mixed in the surface layers of the gainers. This result supports the idea of mixing as an efficient process to remove the abundance anomaly built up by accretion. The chemical evolution of the classical Algol-type systems could lead to constraints on the initial masses of the less massive, evolved, mass-losing stars.Öğe A catalogue of close binaries located in the delta Scuti region of the Cepheid instability strip(Oxford Univ Press, 2006) Soydugan, E.; Soydugan, F.; Demircan, O.; Ibanoglu, C.A catalogue of close eclipsing binary systems (detached and semidetached) with at least one of the components located in the delta Scuti region of the Cepheid instability strip is presented. The positions of the stars in the instability strip are determined by their accurate temperatures and luminosities. Observationally detected binaries (20 semidetached, four detached and one unclassified) with oscillating components were included in the catalogue as a separate table. The primaries of the oscillating Algols tend to be located near the blue edge of the instability strip. Using reliable luminosities and temperatures determined by recent photometric and spectroscopic studies, we have found that at least one or two components of 71 detached and 90 semidetached systems are located in the delta Scuti region of the Cepheid instability strip. In addition, 36 detached or semidetached systems discovered by the Hipparcos satellite were also given as a separate list. One of their components is seen in the delta Scuti region, according to their spectral type or B - V colours. They are potential candidate binaries with the delta Scuti-type pulsating components which need further photometric and spectroscopic studies in better precision. This catalogue covers information and literature references for 25 known and 197 candidate binaries with pulsating components.Öğe The first comprehensive catalog of gamma Dor pulsators and their characteristics(Elsevier Science Bv, 2018) Ibanoglu, C.; Cakirli, O.; Sipahi, E.We present the first comprehensive catalog of the gamma Doradus type pulsating stars. This catalog covers observational properties of all gamma Dor variables obtained until January 2017. The photometric and physical properties of 109 well - known gamma Dor pulsators, 18 hybrid stars, 13 anomalous gamma Dor stars, and 22 gamma Dor stars in eclipsing plus 1 non-eclipsing SB2 binary systems are presented as separate tables. In addition, 291 candidate gamma Dor variables discovered by CoRot, 307 candidate gamma Dor, 205 hybrid and 11 candidate gamma Dor in binaries discovered by Kepler were also presented. Distribution of the genuine single gamma Dor pulsators in the P-puls-T-eff, Amplitude-T-eff, Amplitude-P-puls, and L-T-eff diagrams are presented and discussed. We find following correlations for the gamma Dor pulsators in the eclipsing binaries: P-puls proportional to P-orb(0.27), P-puls proportional to Q(0.45), and P-puls proportional to r(-0.44), where (Q) is the pulsation constant and r is the fractional radius of the pulsating component in the binary system. The correlation coefficients are not high enough due to limited sample and scattering in the data.Öğe Is NP Aqr a new near-contact binary?(Elsevier Science Bv, 2010) Ibanoglu, C.; Cakirli, Oe; Dervisoglu, A.We present radial velocities of the double-lined spectroscopic binary NP Aqr. The radial velocities and the optical light curves obtained by Hipparcos and ASAS-3 are analyzed separately. The masses of the primary and secondary components have been found to be 1.65 +/- 0.09 and 0.99 +/- 0.05 M-circle dot, respectively. The cross-correlation functions indicate triple peaks which show the presence of a tertiary star. The spectroscopic properties of this additional component resemble those of the primary star. The analysis of the light curves has shown that the more massive primary star filling its corresponding Roche lobe. The secondary component is at or near Roche lobe indicating a new beta Lyrae-type near-contact binary. The orbital inclination is about 40 degrees and, therefore, the observed light variations are produced only by the proximity effects. Due to the absence of eclipses, the effective temperature of the secondary star and the radii of the components could not be determined accurately. We conclude that NP Aqr is a non-eclipsing double-lined spectroscopic binary with a distance of about 134 +/- 7pc. The absolute parameters of the components are also compared with the evolutionary models. While the location of the primary star seems to be suitable with respect to its mass in the Hertzsprung-Russell diagram, the secondary component is located close to a star having a mass less than 0.6 M-circle dot. This discrepancy is originated from very low effective temperature determined only from the light curve produced by the proximity effects. The distance to the third star appears to be very close to that of the close binary which indicates that it may be dynamically bounded to the binary. (C) 2009 Elsevier B.V. All rights reserved.Öğe Long-term orbital period behaviors of the neglected Algol type binaries: CC Herculis and XZ Aquilae(Wiley-V C H Verlag Gmbh, 2006) Soydugan, F.; Soydugan, E.; Ibanoglu, C.; Demircan, O.Orbital period variations of two neglected Algol type binaries, CC Her and XZ Aql, are studied based on all available times of minima. In the case of CC Her, it is found that the O-C curve displays a tilted sinusoidal variation with an eccentricity of 0.54 +/- 0.03 and a period of 52.4 +/- 0.4 yr, which can be explained by the light-time effect due to the presence of an unseen component. The course of the orbital period change in XZ Aql appears less reliable but its O-C curve can be represented by a periodic variation with a period of 36.7 +/- 0.6 yr superimposed on an upward parabola. The parabolic variation indicates a secular period increase with a rate of dP/dt = 7.1 s per century. The corresponding conservative mass transfer from less massive component to the more massive one is about 3.26 x 10(-7) M-circle dot yr(-1). It is interesting to see that the O-C variation of CC Her displays no evidence (as upward parabola) on the mass transfer characteristic for Algols. The periodic change of the orbital period of XZ Aql, like CC Her, may be caused by the presence of the third-body. The lower limits of the masses of the hypothetical unseen components for CC Her and XZ Aql are found to be 2.69 M-circle dot and 0.47 M-circle dot, respectively. The third body of CC Her should be detectable not only spectroscopically but also photoelectrically, if it exists. (c) 2006 WILEY-VCH Verlag GmbH& Co. KGaA, Weinheim.Öğe LONG-TERM PHOTOMETRIC AND SPECTROSCOPIC OBSERVATIONS OF THE NEAR-CONTACT BINARY KR CYGNI(Univ Nacional Autonoma Mexico, Inst De Astronomia, 2013) Sipahi, E.; Ibanoglu, C.; Cakirli, O.We present the multi-color, five-year light curves and the radial velocities of the near-contact binary system KR Cyg. We derived the masses of the components as 2.88 +/- 0.20 M-circle dot and 1.26 +/- 0.07 M-circle dot and the radii as 2.59 +/- 0.06 R-circle dot and 1.80 +/- 0.04 R-circle dot. We also searched for the empirical determination of albedo and effective temperature of the cooler, less massive star of KR Cyg, and of two similar near contact binaries AK CMi, and DO Cas. The residuals between the observed and computed fluxes are attributed to the effect of mutual illumination which heats the surface layers of the illuminated star and does vary not only its bolometric albedo but also its limb-darkening coefficient and gravity-brightening exponent. The effective albedos are generally smaller than that expected from an envelope of convective star. These results are preliminary and speculative.Öğe Multimode pulsations of the lambda bootis star 29 Cygni: The 1995 and 1996 multisite campaigns(Univ Chicago Press, 2007) Mkrtichian, D. E.; Kusakin, A. V.; De Coca, P. Lopez; Krisciunas, K.; Akan, C.; Malanushenko, V. P.; Paparo, M.; Percy, J.; Rolland, A.; Costa, V.; Olivares, J. I.; Koval, V. A.; Hobart, M. A.; Ibanoglu, C.; Ozturk, A.; Thompson, S.; Paunzen, E.; Handler, G.; Burnashev, V.; Weiss, W. W.; Kuratov, K. S.; Kang, Y. W.In this paper we present the results of multisite photometric and spectroscopic campaigns, carried out during the years 1995 and 1996, to study the pulsations of a typical lambda Bootis star, 29 Cyg. During the 1995 campaign we found well-defined multiperiodicity in 29 Cyg, which was studied in detail during a multilongitude campaign covering a 65 day time interval in 1996. The frequency analysis of the 1996 campaign's data easily revealed 11 excited low l degree modes with frequencies of oscillation ranging from 20.3 to 37.4 cycles day(-1) and mean photometric amplitudes ranging from 10.65 to 0.96 mmag in the V filter. After removing the well-identified frequencies, the discrete Fourier transform of the residuals showed excess power in the 20-40 cycle day(-1) domain, which indicates the probable existence of unresolved rich p-mode spectra with photometric V amplitudes below 0.5 mmag. We found a regular spacing of 2.41 cycles day(-1) within the modes of 29 Cyg, which was interpreted as the spacing of consecutive even and odd l-values. The asteroseismic luminosity log L/L-circle dot = 1.12, calculated from the frequency spacing, is in good agreement with the Hipparcos luminosity log L/L-circle dot = 1.16 and with luminosities from photometric and spectroscopic calibrations. Using our multicolor photometry we tentatively identified the dominant f(1) 37.425 cycle day(-1) mode as an l = 2, n = 5mode, and made radial overtone identification for all frequencies. These ranged from n 2 to 5. Analysis of the photometric data shows the long-term ( years) and probable short-term ( days) variability of amplitudes for all of these modes in 29 Cyg. Using our multicolor WBVR filter photometry, we found the wavelength dependence of the pulsation amplitudes for the five highest amplitude modes. Based on the H alpha line radial velocity observations of 29 Cyg, we detected multiperiodic radial velocity variations with frequencies of 38.36 and 29.99 cycles day(-1) and semiamplitudes of 1.0 and 0.8 km s(-1), respectively. These frequencies coincide within the errors with the photometric frequencies of the two highest amplitude modes, 37.425 and 29.775 cycles day(-1). For the highest amplitude l = 2, n= 5 mode ( 37.425 cycles day(-1)), the radial velocity-to-light amplitude ratio and velocity-to-light phase shift are equal to 2K(H alpha)/Delta V 94 km mag(-1) s(-1) and Phi(f1) = phi(Vr) - phi V = +0: 08 +/- 0.01, respectively, and are in good agreement with values for delta Scuti stars. The rich multiperiodic spectrum makes 29 Cyg a promising target for future multisite campaigns.Öğe MY Serpentis: a high-mass triple system in the Ser OB2 association(Oxford Univ Press, 2013) Ibanoglu, C.; Cakirli, O.; Sipahi, E.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 d. The radial velocities and the previously published UBV data obtained by Mayer et al. and the UBVRI light curves by Davidge & Forbes are analysed for the physical properties of the components. We determine the following absolute parameters: for the primary star M-p = 32.23 +/- 0.54 M-circle dot, R-p = 14.23 +/- 0.75 R-circle dot; and for the secondary star M-s = 30.59 +/- 0.53M(circle dot), R-s = 13.89 +/- 0.75 R-circle dot. Photoelectric times of minimum light are analysed under the consideration of the light-time orbit. The centre-of-mass of the eclipsing binary is orbiting around the common centre-of-gravity of the triple system with a period of 21.2 +/- 0.7 yr and with a projected semi-major axis of 5.5 +/- 0.7 au. The mass function for the third star was calculated as 0.370 +/- 0.036 M-circle dot. The light contributions of the third star to the triple system in the UBV passbands were derived and the intrinsic magnitudes and colours were calculated individually for the three stars. The components of the eclipsing pair were classified as O7.5III and O9.5III. The intrinsic colour indices for the third star yield a spectral type of (O9.5-B0) III-I. This classification leads to constrain the inclination of the third-body orbit, which should be about 30 degrees, and therefore its mass should be about 29 M-circle dot. MY Ser is one of the rare massive O-type triple system at a distance of 1.65 +/- 0.13 kpc, the same as for the NGC 6604 embedded in the Ser OB2 association.Öğe A new low-mass eclipsing binary: NSVS 02502726(Elsevier Science Bv, 2009) Cakirh, O.; Ibanoglu, C.; Gungor, C.We present optical spectroscopy and extensive RI differential photometry of the double-lined eclipsing binary NSVS 02502726 (2MASS J08441103+5423473). Simultaneous solution of two-band light curves and radial velocities permits determination of precise empirical masses and radii for both components of the system. The analysis indicates that the primary and secondary components of NSVS 02502726 are in a circular orbit with 0.56-day orbital period and have stellar masses of M(1) = 0.714 +/- 0.019 M(circle dot), and M(2) = 0.347 +/- 0.012 M(circle dot). Both of the components have large radii, being R(1) = 0.645 +/- 0.006 R(circle dot), and R(2) = 0.501 +/- 0.005 R(circle dot). The principal parameters of the mass and radius of the component stars are found with an accuracy of 3% and 1%, respectively. The secondary component's radius is significantly larger than model predictions for its mass, similar to what is seen in almost all of the other well-studied low-mass stars which belong to double-lined eclipsing binaries. Strong H(alpha) emission cores and considerable distortion at out-of-eclipse light curve in both R and I bandpasses, presumably due to dark spots on both stars, have been taken as an evidence of strong stellar activity. The distance to system was calculated as 173 +/- 8 pc from the BVRIJHK magnitudes. The absolute parameters of the components indicate that both components are close to the zero-age main-sequence. Comparison with current stellar evolution models gives an age of 126 +/- 30 Myr, indicating the stars are in the final stages of pre-main-sequence contraction. (C) 2009 Elsevier B.V. All rights reservedÖğe Observations of faint eclipsing cataclysmic variables(Elsevier Science Bv, 2010) Camurdan, D. Zengin; Ibanoglu, C.; Camurdan, C. M.We present time-resolved photometry of six faint (V > 17 mag) cataclysmic variables (CVs); one of them is V849 Oph and the others are identified from the Sloan Digital Sky Survey (SDSS J0920+0042, SDSS J1327+6528, SDSS J1227+5139, SDSS J1607.02+3623, SDSS J1457+5148). The optical CCD photometric observations of these objects were performed at the TUBITAK National Observatory (Turkey) between February 2006 and March 2009. We aimed to detect short time scale orbital variability arisen from hot-spot modulation, flickering structures which occur from rapid fluctuations of material transferring from red star to white dwarf and orbital period changes for selected short-period (P < 4 h) CVs at quiescence. Results obtained from eclipse timings and light curves morphology related to white dwarf stars, accretion disks and hot-spots are discussed for each system. Analysis of the short time coverage of data, obtained for SDSSJ1227+5139 indicates a cyclical period change arisen from magnetic activity on the secondary star. Photometric period of SDSS J11607+3623 is derived firstly in this study, while for the other five systems light elements are Corrected using the previous and new photometric observations. The nature of SDSS J1457+5148 is not precisely revealed that its light curve shows any periodicity that could be related to the orbital period. (C) 2009 Elsevier B.V. All rights reserved.Öğe Photometric observations and orbital period variations of HS 0705+6700 and NY Vir(Elsevier Science Bv, 2012) Camurdan, C. M.; Camurdan, D. Zengin; Ibanoglu, C.We present photometric observations of two post-common-envelope stars, NY Vir (=PG 1336-018) and HS 0705 + 6700. The V band CCD observation of NY Vir was performed by a 40 cm telescope at Ege University Observatory and the R band observations of HS 0705 + 6700 were performed by 100 cm telescope at TUBITAK National Observatory. The new light curves were analyzed by the WD code and the physical parameters of stars were determined. We obtained new mid-eclipse timings for HS 0705 + 6700 and combined them with those previously published data. The analysis of the O-C residuals yields a period of about 8.06 +/- 0.28 yr and an amplitude of 98.5 s for the system HS 0705 + 6700, which is attributed to the third star physically bounded to the evolved eclipsing pair. A mass function of 1.2 x 10(-4)M(circle dot) for the third star is obtained. The existence of a third star is also confirmed by the light curve analysis, indicating light contribution of about 0.043 at phase 0.25 in R-bandpass of the eclipsing pair. Using mass-luminosity relationship of the low mass stars we estimate a mass of 0.12 M(circle dot), with an orbital inclination of about 20 degrees The O-C residuals obtained for the system NY Vir were represented by a downward parabola which indicates orbital period decrease in the system. Using the coefficient of quadratic term we calculate a rate of orbital period decrease of about dP/dt= -4.09 x 10(-8)days yr(-1). The period decrease we have measured in NY Vir may be explained by angular momentum loss from the binary system. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.Öğe Preliminary results on the fundamental parameters of the eclipsing binary V398 Lacertae*(Wiley-V C H Verlag Gmbh, 2007) Cakirli, Oe.; Frasca, A.; Ibanoglu, C.; Soydugan, F.; Degirmenci, Oe.The Hipparcos Space Astrometry Mission photometric observations of V398 Lac, led to the discovery of its variability, allowing to classify it as an eclipsing binary with an orbital period of about 5.4 days. This prompted us to acquire high-resolution echelle spectra with the aim of performing accurate radial velocity measurements and to determine the main physical parameters of the system's components. We present, for the first time, a double-lined radial velocity curve and determine the orbital and physical parameters of the two components, that can be classified both as late B-type stars. In particular, we obtained an orbital inclination i similar to 85 degrees. With this value of the inclination, we deduced masses M-1 = 3.83 +/- 0.35 M-circle dot and M-2 = 3.29 +/- 0.32 M-circle dot, and radii R-1 = 4.89 +/- 0.18 R-circle dot and R-2 = 2.45 +/- 0.11 R-circle dot for the more massive and less massive components, respectively. Both components are well inside their own Roche lobes. The mass ratio is M-2/M-1, similar to 0.86. We derived also the projected rotational velocities as v(1) sin i = 79 +/- 2 km s(-1) and v(2) Sin i = 19 +/- 2 km s(-1). Our measurements indicate that the rotation of the primary star is essentially pseudo-synchronized with the orbital velocity at the periastron, while the secondary appears to rotate very slowly and has not yet attained synchronization. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.Öğe Spectroscopic and photometric observations of selected Algol-type binaries - I. V1665 Aquilae and AG Arietis(Blackwell Publishing, 2007) Ibanoglu, C.; Evren, S.; Tas, G.; Cakirli, Oe.; Bozkurt, Z.; Afsar, M.; Frasca, A.; Sipahi, E.; Dal, H. A.; Oezdarcan, O.; Camurdan, D. Zengin; Camurdan, M.; Gandolfi, D.We present the first radial velocities and ground-based photometric observations of V1665 Aql and AG Ari. These double-lined eclipsing binaries have eccentric orbits with eccentricities of 0.24 and 0.09, respectively. New UBV photometric data and radial velocities were analysed using a modified version of the Wilson-Devinney program for the parameters of the systems. Good phase coverage and relatively small scatter both in the light and in the radial-velocity curves meant that the eccentricity and the argument of periastron as well as orbital and stellar parameters could be determined. Our solutions indicate that AG Ari includes a third light with a considerable amount of 5.6 per cent in U, 6.4 per cent in B, and 9 per cent in V. By comparing its light contribution with the total light we classified it as an F-type star. The components in each system are of very nearly equal mass, temperature, and luminosity. Their absolute parameters were compared with those of stars belonging to well-studied detached eclipsing binaries. The components lie well inside the main-sequence band. In addition, the apsidal motion rates of the system have been determined from an analysis of all the photometric observations obtained by space missions and by us. We determined the preliminary apsidal motion periods of the systems to be 449 +/- 34 yr for V1665 Aql and 155 +/- 6 yr for AG Ari. Because well-detached eclipsing binaries are optimal distance indicators, we estimated the distances to V1665 Aql and AG Ari to be 477 +/- 40 and 292 +/- 18 pc from the determined absolute visual magnitudes and interstellar extinction. A comparison with evolutionary tracks indicates that the primary component of V1665 Aql has an age of about 1.6 x 10(8) yr and is near the main-sequence terminal age. The components of AG Ari are intermediate-mass main-sequence stars with an age of about 5.6 x 10(8) yr.Öğe Spectroscopic and photometric observations of the selected Algol-type binaries - III. LL Aquarii, MP Delphini and NSV 20913(Wiley-Blackwell, 2008) Ibanoglu, C.; Evren, S.; Tas, G.; Cakirli, Oe.; Bozkurt, Z.; Afsar, M.; Sipahi, E.; Dal, H. A.; Ozdarcan, O.; Camurdan, D. Zengin; Camurdan, M.; Frasca, A.We present new radial velocities and photometric observations of three double-lined eclipsing binaries LL Aqr, MP Del and NSV 20913. This paper is the third in the planned series of investigations. Standard wide-band indices for the systems and comparison stars were determined accurately. Using the times of mid-eclipses, new ephemerides are calculated for the three systems. These systems consist of two well-detached components in eccentric orbits. The effective temperatures of the hotter components and reddening of the systems have been estimated from Johnson wide-band UBV photometric calibrations. New UBV photometric data and radial velocities were analysed simultaneously for the systems' parameters using Wilson Devinney ( WD) code. The masses have been found to be 1.223 +/- 0.058, 1.056 +/- 0.051; 1.559 +/- 0.085, 1.248 +/- 0.074; 1.76 +/- 0.13 and 1.28 +/- 0.11 M(circle dot) for the primary and secondary stars of LL Aqr, MP Del and NSV20913, respectively. The radii of the components are derived in the case of LL Aqr: 1.325 +/- 0.020, 1.005 +/- 0.016; in those of MP Del: 2.428 +/- 0.046, 1.575 +/- 0.030; and NSV20913: 3.243 +/- 0.081, 1.291 +/- 0.033 R(circle dot). The masses, radii and effective temperatures of the component stars have been determined with an accuracy of 5-8, 2-3 and 1-3 per cent, respectively. We have calculated the distances to the systems of LL Aqr, MP Del and NSV 20913 as 123 +/- 9, 149 +/- 7 and 246 +/- 9 pc, respectively, using bolometric magnitudes and empirical bolometric corrections for the component stars. The stellar model prediction match the measured properties of LL Aqr for an age of about 1.78 Gyr, indicating the components near the half of their core-hydrogen-burning lifetimes. However, the components of MP Del have an age of 1.59 Gyr, the primary component being turn off from the main sequence. The age of the NSV20913's components is about 1 Gyr, indicating the primary component seems to have evolved just slightly off the main sequence but the less massive secondary component is still close to the zero- age main sequence. A subsolar fractional metal abundance, Z approximate to 0.008, provides a better match to the absolute parameters of all three systems.
