Yazar "Surgit, Derya" seçeneğine göre listele

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    Absolute parameters of three southern eclipsing binaries: DQ Car, BK Ind, and V4396 Sgr
    (Oxford Univ Press, 2020) Surgit, Derya; Erdem, Ahmet; Engelbrecht, Chris A.; Marang, Fred
    We present combined photometric and spectroscopic analyses of the three southern eclipsing binary stars: DQ Car, BK Ind, and V4396 Sgr. Radial velocity curves of these three systems were obtained at the South African Astronomical Observatory, and their light curves from the available data bases and surveys were used for the analysis. 75 new times of minima for these three eclipsing binaries were derived, and their ephemerides were updated. Only the O-C diagram of DQ Car indicates a cyclical variation, which was interpreted in terms of the light-time effect due to a third body in the system. Our final models describe these three systems as Algol-like binary stars with detached configurations. The masses and radii were found to be M-1 = 1.86(+/- 0.17) M-circle dot, R-1 = 1.63(+/- 0.06) R-circle dot and M-2 = 1.74(+/- 0.17) M-circle dot, R-2 = 1.52(+/- 0.07) R-circle dot for the primary and secondary components of DQ Car; M-1 = 1.16(+/- 0.05) M-circle dot, R-1 = 1.33(+/- 0.03) R-circle dot and M-1 = 0.98(+/- 0.04) M-circle dot, R-2 = 1.00(+/- 0.03) R-circle dot for BK Ind; and M-1 = 3.14(+/- 0.22) M-circle dot, R-1 = 3.00(+/- 0.09) R-circle dot and M-2 = 3.13(+/- 0.24) M-circle dot, R-2 = 2.40(+/- 0.08) R-circle dot for V4396 Sgr, respectively. The distances to DQ Car, BK Ind, and V4396 Sgr were derived to be 701(+/- 50), 285(+/- 20), and 414(+/- 30) pc from the distance modulus formula, taking into account interstellar extinction. The evolutionary status of these three systems was also studied. It has been found that the components of DQ Car arc very young stars at the age of similar to 25 Myr and those of BK Ind and V4396 Sgr are evolved main-sequence stars at the ages of similar to 2.69 Gyr and similar to 204 Myr, respectively.
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    Apsidal motion and absolute parameters of GV Nor and V881 Sco based on mid-resolution spectroscopy and TESS photometry
    (Oxford Univ Press, 2023) Surgit, Derya; Zasche, Petr; Hadrava, Petr; Erdem, Ahmet; Engelbrecht, Chris A.; Marang, Fred; Masek, Martin
    The veracity of stellar evolution models and theoretical internal structure constants may be subjected to stringent tests by using physical parameters obtained from spectroscopic and photometric observations of eclipsing binary systems that exhibit apsidal motion. Two eclipsing binary stars from the southern hemisphere with no prior published spectroscopic analyses were selected for this study: GV Nor and V881 Sco. Spectroscopic observations of these two eccentric binary systems were made at the South African Astronomical Observatory (SAAO) in 2018 and 2019, and their mid-resolution spectra were obtained. The radial velocities were measured using the cross-correlation method as well as by disentangling the spectra. The rotational broadening of the disentangled spectra of the components was also determined. The absolute parameters of these two systems were obtained by analyzing the SAAO-based spectroscopic data in conjunction with photometric data from Transiting Exoplanet Survey Satellite. Apsidal motion parameters for these two eccentric binary systems were calculated by analysing eclipse timing variations. Granada and Padova evolution models indicated ages of 340 +/- 35 Myr for GV Nor and 760 +/- 15 Myr for V881 Sco, in agreement with the observational results. The theoretical internal structure constants estimated from the Granada models were compatible with the observational values within the error limits. However, for both systems, it was found that their circularization and synchronization timescales were shorter than their respective evolutionary ages. Therefore, the fact that the components rotate faster than their synchronized values and still have rather large eccentric orbits (e similar to 0.11) challenges present theories of circularization and spin-orbit synchronization.
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    New Spectroscopic Solution of the Eclipsing Binary HX Vel A
    (Astronomical Soc Pacific, 2015) Surgit, Derya; Erdem, Ahmet; Ozkardes, Burcu; Butland, Roger; Budding, Edwin
    We present a preliminary analysis of new spectroscopic observations of the southern binary HX Vel A. High-resolution spectroscopic observations were made at the Mt. John University Observatory in 2014. Radial velocities for HX Vel A were determined from the Gaussian profile-fitting method. The Keplerian radial velocity model gives the close binary mass ratio as 0.57 +/- 0.06. The resulting orbital elements are ai sin i = 0.0086 +/- 0.0003 au, a(2) sin i = 0.0151 +/- 0.0003 au, M-1 sin(3) i = 0.887 +/- 0.046 M-circle dot, and M-2 sin(3) i = 0.504 +/- 0.032 M-circle dot.
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    On the nature of the eccentric eclipsing binary star SY Phe with a pulsating ? Dor component
    (Oxford Univ Press, 2024) Erdem, Ahmet; Surgit, Derya; Engelbrecht, Chris A.; Zasche, Petr; Bakis, Volkan; Marang, Fred
    Spectroscopic observations of the eccentric binary system SY Phe were made at the South African Astronomical Observatory in 2019, 2020, and 2021, and its mid-resolution spectra were obtained. The radial velocities of the component stars were measured using the cross-correlation method and Fourier disentangling of the spectra. The spectral type (hence the effective temperature) of the primary star was determined from a model-atmosphere analysis. The radial velocity and Transiting Exoplanet Survey Satellite ( TESS ) light curves of the system were analysed, and its absolute parameters were derived. A strong (5.2 mmag) periodic signal with a frequency typical of gamma Dor stars (1.169 cycles per day) dominates the Fourier spectrum of the light curve between the eclipses. Apsidal motion parameters of SY Phe were calculated by studying eclipse timing variations. The Geneva evolution models indicate an evolutionary age of 2 Gyr and solar metallicity for the primary component; however, although the position of the secondary component in the H-R diagram matches the isochrone of 2Gyr, it appears to have a larger radius and higher effective temperature than expected for its determined mass. Here, the secondary component has too large a radius, which is in accordance with the radius discrepancy problem that has been encountered in other studies, especially in late-type dwarfs, and has not been solved for half a century.
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    Spectroscopic Study of the Early-Type Binary HX Vel A
    (Cambridge Univ Press, 2012) Ozkardes, Burcu; Surgit, Derya; Erdem, Ahmet; Budding, Edwin; Soydugan, Faruk; Demircan, Osman
    This paper presents high resolution spectroscopy of the HX Vel (IDS 08390-4744 AB) multiple system. New spectroscopic observations of the system were made at Mt. John University Observatory in 2007 and 2008. Radial velocities of both components of HX Vel A were measured using gaussian fitting. The spectroscopic mass ratio of the close binary was determined as 0.599 +/- 0.052, according to a Keplerian orbital solution. The resulting orbital elements are a(1)sini=0.0098 +/- 0.0003 AU, a(2)sini=0.0164 +/- 0.0003 AU, M(1)sin(3)i=1.19 +/- 0.07 M-circle dot and M(2)sin(3)i=0.71 +/- 0.04 M-circle dot.
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    V410 Puppis: A useful laboratory for early stellar evolution
    (Oxford Univ Press, 2022) Erdem, Ahmet; Surgit, Derya; Ozkardes, Burcu; Hadrava, Petr; Rhodes, Michael D.; Love, Tom; Blackford, Mark G.
    New spectrometric (HERCULES) and ground-based multicolour photometric data on the multiple star V410 Puppis are combined with satellite photometry (HIPPARCOS and TESS), as well as historic astrometric observations. Absolute parameters for V410 Pup Aab are derived: M-Aa = 3.15 +/- 0.10, M-Ab = 1.83 +/- 0.08 (M-circle dot); R-Aa = 2.12 +/- 0.10, R-Ab = 1.52 +/- 0.08 (R-circle dot); a = 6.57 +/- 0.04 R-circle dot; T-Aa = 12500 +/- 1000, T-Ab = 9070 +/- 800(K), and photometric distance 350 +/- 10 (pc). We report the discovery of a low-amplitude SPB variation in the light curve and also indications of an accretion structure around V410 Pup B as well as emission cores in V410 Pup C. We argue that V410 Pup is probably a young formation connected with the Vela 2 OB Association. The combined evidence allows an age in the range 7-25 Myr from comparisons with standard stellar evolution modelling.