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A W UMa type system from Southern Hemisphere: CN Hydri
(Elsevier, 2009) Ozkardes, B.; Erdem, A.; Bakis, V.
We present an analysis of the Hipparcos photometry and the high-resolution (lambda/Delta lambda = 41000) spectroscopy of the W UMa type system CN Hyi obtained in this study for the first time. The high resolution spectroscopic observations of the system were made at Mt. John University Observatory by using HERCULES fibre-fed echelle spectrograph in September 2007. The radial velocities of the component stars of the system were determined by using the spectral disentangling technique. The orbital solution of CN Hyi yielded the spectroscopic mass ratio as 0.189. We performed the simultaneous solution of the Hipparcos light curve and the radial velocity curves. The light contribution of the third star to the total light of the system was also considered during our photometric analysis. The Simultaneous solutions yielded the absolute parameters of the system as M-1 = 1.37 M-1, M-2 = 0.25 M-2 for the masses, R-1 = 1.60 R-1, R-2 = 0.77 R-2, for the radii, and M-v.1, = 3(m).23, M-v.2 = 4(m).92 for the absolute magnitudes of the primary and secondary components, respectively. The distance of the system was calculated as 56 pc using the distance modulus with the corrections of the interstellar extinction. The positions of the components of CN Hyi in the FIR diagram were also discussed. (C) 2009 Elsevier B.V. All rights reserved.
Absolute dimensions and apsidal motion of the eccentric binary PT Velorum
(Blackwell Publishing, 2008) Bakis, V.; Bakis, H.; Demircan, O.; Eker, Z.
High-resolution (lambda/d lambda similar to 41 000) echelle spectra of the eccentric binary system PT Vel were analysed. Precise spectroscopic orbital elements of the system were obtained by means of cross-correlation technique. According to the solution of radial velocities with Hipparcos and All Sky Automated Survey-3 (ASAS-3) light curves, PT Vel consists of two main-sequence stars with masses M-1 = 2.198 +/- 0.016 M-circle dot, M-2 = 1.626 +/- 0.009 M-circle dot, radii R-1 = 2.094 +/- 0.020 R-circle dot, R-2 = 1.559 +/- 0.020 R-circle dot and temperatures T-eff1 = 9250 +/- 150 K, T-eff2 = 7650 +/- 200 K separated from each other by A = 9.74 +/- 0.02 R-circle dot in an orbit inclined 88.2 degrees +/- 0.5. The projected rotational velocities of component stars were found to be (v sin i)(1) = 63 +/- 2 and (v sin i)(2) = 40 +/- 3 km s(-1) from the comparison of observed spectra with synthetic spectra which were calculated using model atmospheres. Our measurements of the projected rotational velocities indicate that both stars rotate synchronously. Analysis of longitude of periastron values obtained from light-curve analysis from different photometric sets of this moderately eccentric system (e = 0.127 +/- 0.006) has revealed a significant motion of the line of apsides of (w) over dot = 0.0097 +/- 0 degrees.0004 cycle(-1) corresponding to an apsidal motion period of U = 182.2 +/- 8.4 yr. The contribution from general relativity effects is moderate (similar to 9 per cent). A comparison with predictions from interior structure models shows the real stars to be more concentrated in mass than expected. Comparison of absolute dimensions with theoretical isochrones yielded an age of the system of 400 +/- 40 Myr.
Absolute dimensions and apsidal motion of the eccentric binary V731 Cephei
(Oxford Univ Press, 2008) Bakis, V.; Zejda, M.; Bulut, I.; Wolf, M.; Bilir, S.; Bakis, H.; Demircan, O.
A detailed analysis of new and existing photometric, spectroscopic and spatial distribution data of the eccentric binary V731 Cep was performed. Spectroscopic orbital elements of the system were obtained by means of cross-correlation technique. According to the solution of radial velocities with UBVRc and I-c light curves, V731 Cep consists of two main-sequence stars with masses M-1 = 2.577 (0.098) M-circle dot, M-2 = 2.017 (0.084) M-circle dot, radii R-1 = 1.823 (0.030) R-circle dot, R-2 = 1.717 (0.025) R-circle dot and temperatures T-eff1 = 10700 (200) K, T-eff2 = 9265 (220) K separated from each other by a = 23.27 (0.29) R-circle dot in an orbit with inclination of 88 degrees.70 (0.03). Analysis of the O-C residuals yielded a rather long apsidal motion period of U = 10000 (2500) yr compared to the observational history of the system. The relativistic contribution to the observed rates of apsidal motion for V731 Cep is significant (76 per cent). The combination of the absolute dimensions and the apsidal motion properties of the system yielded consistent observed internal structure parameter (log (k) over bar (2,obs) = -2.36) compared to the theory ( log (k) over bar (2,theo) = -2.32). Evolutionary investigation of the binary by two methods (Bayesian and evolutionary tracks) shows that the system is t = 133(26) Myr old and has a metallicity of [M/H] = -0.04(0.02) dex. The similarities in the spatial distribution and evolutionary properties of V731 Cep with the nearby (rho similar to 3 degrees.9) open cluster NGC 7762 suggest that V731 Cep could have been evaporated from NGC 7762.
Active binary R Arae revisited: Bringing the secondary component to light and physical modelling of the circumstellar material
(Oxford Univ Press, 2016) Bakis, H.; Bakis, V.; Eker, Z.; Demircan, O.
The spectral lines of the secondary component of the active binary system R Ara were uncovered for the first time, which allowed directly to determine the parameters of the spectroscopic orbit. The mass ratio of the system is updated to a new observational value of M-2/M-1 = 0.305 +/- 0.005 which is similar to 20 per cent smaller than the literature value (M-2/M-1 = 0.39). Modelling the reconstructed component spectra yielded the equatorial rotational velocities of the components as nu(rot1) = 202 km s(-1) and nu(rot2) = 73 km s(-1) indicating a very fast rotation (similar to 5 times faster than the synchronous rotation velocity) for the primary and synchronous rotation for the secondary component. The circumstellar material in the system was investigated using the Hipparcossatellite data and the high-resolution (R similar to 41 000) spectral data. According to our model, there is always material transferring from the secondary component on to the primary causing a hot region on its surface. The structural difference between the spectra taken at the same orbital phase but at different epochs proved that the density and the velocity of the transferring material are variable. There are three main trends in the light curve and spectral line variations suggesting the activity cycles for the system, namely quiescent, moderate and, active cycles. It was estimated that the circumstellar material around could be extended to large distances up to 40 R-circle dot from the system.
Analysis of ? Librae including Hipparcos astrometry
(Blackwell Publishing, 2006) Bakis, V.; Budding, E.; Erdem, A.; Bakis, H.; Demircan, O.; Hadrava, P.
New spectroscopy of the classical Algol system delta Lib, combined with high-quality optical and infrared photometry, provides the basis for a good understanding of the close binary system's main parameters. Detailed analysis of the photometry reveals the significant role of a third light source, pointing to the existence of a companion to the eclipsing system of mass similar to 1 M-circle dot. We review the methodology of applying high-accuracy positional information, available from the Hipparcos Intermediate Astrometric Data archive, to stars that may have such companions. Analysis of the astrometry of delta Lib also points to a third star similar to the one already identified by Worek from radial-velocity data, although with slightly revised parameters. O-C data do not contradict this, but their general precision (while confirming the close pair's Algol status) fails to allow a decision on the third orbit parameters: Worek's or revised ones. Taking the photometry, spectroscopy and astrometry together, however, the existence of a third star of comparable mass to the Sun, as a relatively close companion to the eclipsing binary (similar to 4 au), is confirmed.
Discovery of ? scuti type oscillations in two algol-type binaries: DY Aqr and Bg Peg
(Hungarian Academy of Sciences (Konkoly Observatory), 2009) Soydugan, Esin; Soydugan, Faruk; Enyuz, T.; Puskullu, Q.; Tuysuz, M.; Bakis, V.; Bilir, S.
[No abstract available]
Discovery of new variable stars at the Canakkale Onsekiz Mart University Observatory
(Astronomical Soc Pacific, 2007) Bakis, V.; Bakis, H.; Demircan, O.; Budding, E.; Erdem, A.; Cicek, C.
We present the light curves of five variable stars discovered at the Canakkale Onsekiz Mart University Observatory. From the light curve shapes of the variables we see that GSC 4288 0186 and GSC 4019 3345 are detached, USNO 1500-00409928 is a W UMa-type eclipsing binary, while the others seem to be intrinsic variable stars. By using a 30-cm telescope equipped with an ST237 CCD camera dedicated for times of minima observations, we plan to perform systematic observations to discover new variable stars with the help of automatic data reduction techniques in the future.
Discovery of {delta} Scuti type oscillations in two Algol-type binaries: DY Aqr and BG Peg
(2009) Soydugan, Esin; Soydugan, Faruk; Senyüz, T.; Püsküllü, Ç.; Tüysüz, M.; Bakis, V.; Bilir, S.
[No abstract available]
First ground-based photometry and light-curve analysis of the eccentric eclipsing binary V744 Cas
(Wiley-V C H Verlag Gmbh, 2006) Bulut, I.; Cicek, C.; Erdem, A.; Bakis, V.; Demircan, O.; Degirmenci, O. L.
The first ground-based BVR photometric observations of the recently discovered eclipsing binary V744 Cas are presented. From these measurements, timings for two primary and one secondary minima have been calculated. The light curves of the system were analyzed by using the Wilson-Devinney program. The analysis shows that the system is detached with two similar components of spectral type A2V, and the orbit is eccentric (e = 0.0662 +/- 0.0005). The longitude of the periastron (w) was found significantly different for two different light curves (ours and that of Hipparcos), which is strongly suggestive of an apsidal motion with a period of about 425 +/- 68 yr. This makes V744 Cas an important candidate for studies of apsidal motions. The first estimate of the absolute dimensions place the system close to the terminal age of the main sequence (TAMS) in the HR diagram. The distance from the spectroscopic parallax (d = 740 +/- 10 pc) was found to be slightly larger than the Hipparcos distance of d = 610 +/- 400 pc. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Interrelated main-sequence mass-luminosity, mass-radius, and mass-effective temperature relations
(Oxford Univ Press, 2018) Eker, Z.; Bakis, V.; Bilir, S.; Soydugan, Faruk; Steer, I.; Soydugan, Esin; Bakis, H.
Absolute parameters of 509 main-sequence stars selected from the components of detached eclipsing spectroscopic binaries in the solar neighbourhood are used to study mass-luminosity, mass-radius, and mass-effective temperature relations (MLR, MRR, and MTR). The MLR function is found better if expressed by a six-piece classical MLR (L proportional to M-alpha) rather than a fifth or a sixth degree polynomial within the mass range of 0.179 < M/M-circle dot <= 31. The break points separating the mass ranges with classical MLR do not appear to us to be arbitrary. Instead, the data indicate abrupt changes along the mass axis in the mean energy generation per unit of stellar mass. Unlike the MLR function, the MRR and MTR functions cannot be determined over the full range of masses. A single-piece MRR function is calibrated from the radii of stars with M <= 1.5M(circle dot), while a second single-piece MTR function is found for stars with M > 1.5M(circle dot). The missing part of the MRR is computed from the MLR and MTR, while the missing part of the MTR is computed from the MLR and MRR. As a result, we have interrelated the MLR, MRR, and MTR, which are useful in determining the typical absolute physical parameters of main-sequence stars of given masses. These functions are also useful to estimate typical absolute physical parameters from typical T-eff values. Thus, we were able to estimate the typical absolute physical parameters of main-sequence stars observed in the Sejong Open cluster Survey, based on that survey's published values for T-eff. Since typical absolute physical parameters of main-sequence stars cannot normally be determined in such photometric surveys, the interrelated functions are shown to be useful to compute such missing parameters from similar surveys.
? Muscae
(Wiley-Blackwell, 2007) Bakis, V.; Bakis, H.; Eker, Z.; Demircan, O.
High-resolution (lambda/d lambda similar to 41 000) echelle spectra of the multiple system eta Muscae were analysed. Precise spectroscopic orbital elements of the close pair eta Muscae-A were obtained by means of two techniques; cross-correlation and spectral disentangling. The updated light elements of the close pair were derived using new photometric and spectroscopic data together with Hipparcos ephemerides. According to simultaneous studies of radial velocities with Hipparcos light curve and recent and historic light curves in Stromgren bands, eta Mus-A consists of two quasi-identical components: M(1) =3.30 M., M(2) = 3.29 M., R(1) = 2.14 R., R(2) = 2.13 R., T(1)=12 700 K and T(2) = 12 550 K separated from each other by a = 14.11 R. in an orbit inclined 77 degrees.4. The membership of eta Mus-A to the Lower Centaurus-Crux OB association is discussed. The rotational velocity of the primary component was found to be smaller than that of the secondary component. The asynchronous slow rotation of the primary and the synchronous rotation of the secondary imply a recent decrease in the orbital period, either due to orbital angular momentum being transferred to the visual companion eta Mus-C or due to relatively frequent stellar encounters in this crowded region. The visual companion eta Mus-B is found to be gravitationally unbound to the close pair eta Mus-A. The radial velocity measurements of the visual companion eta Mus-B, when combined with its positional information, support its membership to the Lower Centaurus-Crux OB association, but the evidence for membership of eta Mus-A is weaker.
Nature of the Multiple System V831 Centauri
(Astronomical Soc Pacific, 2010) Bakis, V.; Hensberge, H.; Demircan, O.
We present a comprehensive analysis results of the high-resolution spectra together with photometric data of the multiple system V831 Centaurus. Using spectral disentangling technique on the spectroscopic data with information from multi-band Geneva photometry, the disentangled spectra of the close binary components and the third star were obtained together with the spectroscopic orbital elements. The mass ratio of the close binary was found to be q=0.805. The disentangled spectra of the close binary components present a characteristic behavior of mid-B spectral type star while the third star's spectrum is more consistent with a mid-F spectral type main-sequence star.
New Discovered Pulsational Components in Algol Type Binaries and their Positions on the plane of Porb-Ppuls
(Astronomical Soc Pacific, 2010) Soydugan, Esin; Soydugan, Faruk; Senyuz, T.; Tuysuz, M.; Bakis, V.; Bilir, S.; Cicek, C.
In this study, eclipsing binaries located in the delta Scuti region of the instability strip were chosen from the list of candidate eclipsing binary systems with delta Scuti components. These candidate systems were photometrically observed and some of them were announced to be new Algol-type binaries with delta Scuti components. Although the pulsational variability could not be determined for some of the candidate Algols, pulsational components in EW Boo and DY Aqr have been discovered for the first time. The light curves of EW Boo and DY Aqr were analyzed to model the variations caused by the eclipsing behavior and then we determined the pulsational periods and amplitudes of the pulsating components in these Algols. The relationship between the pulsation and orbital periods of the eclipsing binaries were tested and discussed for the cases of EW Boo and DY Aqr.
Northern Binaries in the Evrena Project
(Cambridge Univ Press, 2012) Bakis, V.; Hensberge, H.; Zejda, M.; de Cat, P.; Yilmaz, F.; Bloemen, S.; Svoboda, P.
In the framework of the EVRENA project, high-resolution spectra. of northern eclipsing close binaries in stellar groups are obtained with the HERMES Echelle spectrograph at the Mercator telescope (Roque de los Muchachos Observatory). This contribution gives the first results on DV Camelopardalis.
On the light curve variation of the Be star EM Cep
(Astronomical Soc Pacific, 2007) Bakis, H.; Bakis, V.; Demircan, O.; Budding, E.; Tanriver, M.
We present new UBV photometric observations obtained in the last four observing seasons and one season of spectroscopic observation for the Be star EM Cep. A possible period of 0.403 days and large light amplitude variations from one season to other were determined from the new photometric observations. A flare activity for this star has been detected on 17-18 July 2003. The brightness increase during the flare was found to be maximum in U-band. New spectroscopic observations with high-resolution spectrograph did not present a certain result due to the limited number of data. The type of variability in the light curves shows that the star could be a lambda Eri-type variable. Additional changes on the light curve do not show any periodicity. Binarity problem of the star has been also discussed.
Orbital Parameters Of The Multiple System EM Boo
(Amer Inst Physics, 2018) Ozkardes, B.; Bakis, H.; Bakis, V.
EM Boo is a relatively bright (V = 8.98 mag.) and short orbital period (P similar to 2.45 days) binary star member of the multiple system WDS J14485+2445AB. There is neither photometric nor spectroscopic study of the system in the literature. In this work, we obtained spectroscopic orbital parameters of the system from new high resolution spectroscopic observations made with echelle spectrograph attached to UBT60 telescope of Akdeniz University. The spectroscopic solution yielded the values K-1 = 100.7 +/- 2.6 km/s, K-2 = 120.1 +/- 2.6 km/s and V-gamma = -14.6 +/- 3.1 km/s, and thus the mass ratio of the system q = 0.838 +/- 0.064.
Orbital period variations of four Algol-type eclipsing binaries: SW Cyg, UU Leo, XX Cep and BO Vul
(Wiley-V C H Verlag Gmbh, 2007) Erdem, A.; Dogru, S. S.; Bakis, V.; Demircan, O.
The orbital period behaviours of four Algol-type eclipsing binaries SW Cyg, UU Leo, XX Cep and BO Vul are studied, by using all available times of minimum light in the literature. Their O-C diagrams were represented by long-period sinusoidal variations superimposed on parabolic forms. The parabolic forms for SW Cyg and UU Leo correspond to secular period increases, while for XX Cep and 130 Vul to secular period decreases. To explain these observed secular changes in these four Algol systems, we considered the combined effect of the mass transfer from the less massive component to the more massive one and the mass loss from the system. We concluded that the dominant mechanism for observed long-term period change of SW Cyg and UU Leo is the mass transfer, and that of XX Cep and BO Vul is the mass loss from the systems. It is interesting that the mass transfer rates (i.e., 10-(7)-10(-8) M-circle dot/yr) found for all four Algol binaries are at the upper limit of those generally accepted for Algols. However, assuming the mass loss via circumbinary disks of Chen et al. (2006) reduces the rate to 10(-8)-10(-9) M-circle dot/yr. We interpreted the tilted sinusoidal variations in all cases in terms of the light-time effect due to unseen components in the systems. Unacceptably large hypothetical third body masses in the case of SW Cyg and UU Leo, and common nature of the cyclic O-C variations in semi-detached Algols recall the cyclic magnetic activity effects of the secondary components as the working hypothesis in explaining cyclic period variations of these systems. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Photometric and spectroscopic study of the eclipsing binary GSC 4288 0186
(Astronomical Soc Pacific, 2007) Bakis, V.; Bakis, H.; Budding, E.; Demircan, O.; Zejda, M.
First complete BVRI light curves and radial velocity measurements of the recently discovered eclipsing binary GSC 4288 0186 are presented. Analyses of the light curves, together with spectroscopic data show that the system is a double-lined detached binary with an eccentric orbit. We determined the preliminary values of the absolute elements of this eclipsing binary and presented here.
STUDY OF ECLIPSING BINARY AND MULTIPLE SYSTEMS IN OB ASSOCIATIONS. II. THE CYGNUS OB REGION: V443 Cyg, V456 Cyg, AND V2107 Cyg
(Iop Publishing Ltd, 2014) Bakis, V.; Hensberge, H.; Bilir, S.; Bakis, H.; Yilmaz, F.; Kiran, E.; Demircan, O.
Three presumably young eclipsing binary systems in the direction of the Cygnus OB1, OB3, and OB9 associations are studied. Component spectra are reconstructed and their orbits are determined using light curves and spectra disentangling techniques. V443 Cyg and V456 Cyg have circular orbits while the light curve of V2107 Cyg imposes a slightly eccentric orbit (e = 0.045 +/- 0.03). V443 Cyg harbors F-type stars, not young early-A stars as previously suggested in the literature based solely on photometry. It appears to be situated in the foreground (distance 0.6 +/- 0.2 kpc) of the young stellar populations in Cygnus. V456 Cyg, at a distance of 0.50 +/- 0.03 kpc, consists of a slightly metal-weak A-type star and an early-F star. The age of both systems, on or very near to the main sequence, remains uncertain by an order of magnitude. V2107 Cyg is a more massive system (8.9 +/- 2 and 4.5 +/- 1.2M(circle dot)) at 1.5 +/- 0.5 kpc and, also kinematically, a strong candidate-member of Cyg OB1. The more massive component is slightly evolved and appears to undergo non-radial beta Cep-type pulsations. The Doppler signal of the secondary is barely detectable. A more extensive, asteroseismological study is necessary to fix masses more precisely. Nevertheless, the position of the primary in the H-R diagram confines the age reasonably well to 20 +/- 5 Myr, indicating that for Cyg OB1 has a similar extent of star formation history as that established for Cyg OB2.
The early-type semidetached binary system V716 Centaurus
(Oxford Univ Press, 2008) Bakis, H.; Bakis, V.; Demircan, O.; Eker, Z.
New high-resolution spectra of V716 Cen revealed for the first time lines of the secondary component and its radial velocities. The simultaneous solution of the new radial velocity curves and the Hipparcos light curve yield the reliable absolute dimensions of this semidetached system. The masses for the primary and secondary are M-1 = 5.68 +/- 0.07 M-circle dot and M-2 = 2.39 +/- 0.05 M-circle dot respectively, and the radii are R-1 = 4.08 +/- 0.07 R-circle dot and R-2 = 3.36 +/- 0.02 R-circle dot. We derive also effective temperatures of T-eff1 = 15 500 +/- 50 K and T-eff2 = 9000 +/- 80 K, and equatorial rotational velocities of v(rot) sin i = 137 +/- 2 km s(-1) and v(rot) sin i = 116 +/- 7 km s(-1). These rotational velocities imply that the components rotate synchronously. The distance to the system is d = 339 +/- 8 pc, in good agreement with the less accurate Hipparcos distance (337 +/- 72 pc). The primary is underluminous and the secondary overluminous compared to normal main-sequence stars of the same mass. This implies that the secondary component of the semidetached system is in slow mass transferring stage after mass ratio reversal, although the Ha-line profiles do not show clear evidence for this.

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