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Öğe A Silent Revolution in Fundamental Astrophysics(Iop Publishing Ltd, 2022) Eker, Zeki; Soydugan, Faruk; Bakis, Volkan; Bilir, Selcuk; Steer, IanArbitrariness in the zeropoint of bolometric corrections is a paradigm that is nearly a century old and leads to two more paradigms. Bolometric corrections must always be negative, and the bolometric magnitude of a star ought to be brighter than its V magnitude. Both were considered valid before the IAU 2015 General Assembly Resolution B2, a revolutionary document that supersedes all three aforementioned paradigms. The purpose of this article is to initiate new insight into and a new understanding of the fundamental astrophysics and present new capabilities to obtain standard and more accurate stellar luminosities and gain more from accurate observations in the era after Gaia. The accuracy gained will aid in advancing stellar structure and evolution theories and also Galactic and extragalactic research, observational cosmology, and searches for dark matter and dark energy.Öğe Absolute Dimensions and Apsidal Motion of the Young Detached System LT Canis Majoris(Oxford Univ Press, 2010) Bakis, Volkan; Bulut, Ibrahim; Bilir, Selcuk; Bakis, Hicran; Demircan, Osman; Hensberge, HermanNew high-resolution spectra of the short-period (P similar to 1.76 days) young detached binary LT CMa are reported for the first time. By combining the results from an analysis of new radial-velocity curves and published light curves, we determine values for the masses, radii, and temperatures as follows: M-1 = 5.59 (0.20)M-circle dot, R-1 = 3.56 (0.07) R-circle dot, and T-eff1 = 17000 (500) K for the primary and M-2 = 3.36 (0.14)M-circle dot, R-2 = 2.04 (0.05) R-circle dot, and T-eff2 = 13140 (800) K for the secondary. Static absorbtion features apart from those coming from the close binary components were detected in the several spectral regions. If these absorbtion features are from a third star, as the light-curve solutions support, its radial velocity is measured to be RV3 = 70 (8) km s(-1) The orbit of the binary system has been proved to be eccentric (e = 0.059) and thus apsidal motion exists. The estimated linear advance in longitude of periastron corresponds to an apsidal motion of U = 69 +/- 5 yr for the system. The average internal structure constant, log k(2,obs) = -2.53 of LT CMa, is found to be smaller than its theoretical value of log k(2,theo) = -2.22, suggesting that the stars would have a more central concentration in mass. The photometric distance of LT CMa (d = 535 +/- 45 pc) is found to be much smaller than the distance of the CMa OB1 association (1150 pc), which rules out membership. A comparison with current stellar evolution models for solar metallicity indicates that LT CMa (35 Myr) is much older than the CMa OB1 association (3 Myr), confirming that LT CMa is not a member of CMa OB1. Kinematical and dynamical analyses indicate that LT CMa is orbiting the Galaxy in a circular orbit, and belongs to the young thin-disk population.Öğe Comparative study of the W UMa type binaries S Ant and ? CrA(Cambridge Univ Press, 2024) Bakis, Volkan; Budding, Edwin; Erdem, Ahmet; Love, Tom; Blackford, Mark G.; Wu, Zihao; Tang, AdamContact binaries challenge contemporary stellar astrophysics with respect to their incidence, structure, and evolution. We explore these issues through a detailed study of two bright examples: S Ant and epsilon CrA, that permit high-resolution spectroscopy at a relatively good S/N ratio. The availability of high-quality photometry, including data from the TESS satellite as well as Gaia parallaxes, allows us to apply the Russell paradigm to produce reliable up-to-date information on the physical properties of these binaries. As a result, models of their interactive evolution, such as the thermal relaxation oscillator scenario, can be examined. Mass transfer between the components is clearly evidenced, but the variability of the O'Connell effect over relatively short-time scales points to irregularities in the mass transfer or accretion processes. Our findings indicate that S Ant may evolve into an R CMa type Algol, while the low mass ratio of epsilon CrA suggests a likely merger of its components in the not-too-distant futureÖğe ETAP: An Exoplanetary Transit Analyzer Program(Astronomical Soc Pacific, 2015) Demircan, Osman; Bakis, VolkanWe introduce new software for the modeling of exoplanet transit light curves. The technique is based on the aperture cross correlation between the light changes and the diffraction pattern of the apertures representing the eclipsing binary components (Kopal 1977; Kopal & Demircan 1978), where in the present case the eclipsing component is considered to be a transiting exoplanet. The software finds the best parameters including the fractional radii of the exoplanet and the host star, the inclination and eccentricity of the orbit, the longitude of periastron, limb-darkening coefficients of any degree, and the transit time, yielding the lowest chi(2). Parameter uncertainties are calculated with the jackknife method. We compare results for selected exoplanet transit light curves against those available in the literature.Öğe 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, FredSpectroscopic 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.Öğe Standard UBV Observations at the Canakkale University Observatory (CUO)(Tubitak Scientific & Technological Research Council Turkey, 2005) Bakis, Hicran; Bakis, Volkan; Demircan, Osman; Budding, EdwinBy using standard and comparison star observations carried out at different times of the year, at Canakkale Onsekiz Mart University Observatory, we obtained the atmospheric extinction coefficients at the observatory. We also obtained transformation coefficients and zero-point constants for the transformation to the standard Johnson UBV system, of observations in the local system carried out with the SSP5A photometer and T40 telescope. The transmission curves and the mean wavelengths of the UBV filters as measured in the laboratory appear not much different from those of the standard Johnson system and found inside the transmission curve of the standard mean atmosphere.Öğe Study of Eclipsing Binary and Multiple Systems in OB Associations III: A Progress Report(Astronomical Soc Pacific, 2015) Bakis, Volkan; Hensberge, Herman; Demircan, Osman; Zejda, Miloslav; Bilir, Selcuk; Nitschelm, ChristianOur international collaboration is devoted to the observation and analysis of young eclipsing binary and multiple systems in various OB associations. Preliminary results reveal several higher-multiplicity systems. Modern analysis techniques such as spectral disentangling and comprehensive atmosphere modeling enable us to derive the atmospheric properties of the distant companions as well as the astrophysical parameters of the eclipsing binary components with high accuracy.Öğe Study of Eclipsing Binary and Multiple Systems in OB Associations. I. Orion OB1a-IM Monocerotis(Oxford Univ Press, 2011) Bakis, Hicran; Bakis, Volkan; Bilir, Selcuk; Mikulasek, Zdenek; Zejda, Miloslav; Yaz, Esma; Demircan, OsmanAll available photometric and spectroscopic observations were collected and used as the basis of a detailed analysis of the close binary IM Mon. The orbital period of the binary was refined to 1(d). 19024249 (0.00000014). The Roche equipotentials, fractional luminosities (in B, V, and Hp-bands) and fractional radii for the component stars in addition to the mass ratio, q, inclination, i, of the orbit, and the effective temperature, T-eff,, of the secondary cooler less massive component were obtained by the analysis of light curves. IM Mon is classified to be a detached binary system in contrast to the contact configuration estimations in the literature. The absolute parameters of IM Mon were derived by the simultaneous solutions of light and radial-velocity curves as M-1.2 = 5.50 (0.24) M-circle dot and 3.32 (0.16) M-circle dot, R1,2 = 3.15 (0.04) R-circle dot and 2.36 (0.03) R-circle dot, T-eff1.2 = 17500 (350) K and 14500 (550) K implying spectral types of B4 and B6.5 ZAMS stars for the primary and secondary components, respectively. The modelling of the high-resolution spectrum revealed the rotational velocities of the component stars as 17(rot1) = 147 (15) km s(-1) and V-rot2 = 90 (25)km s(-1). The photometric distance of 353 (59) pc was found to be more precise and reliable than the Hipparcos distance of 341 (85) pc. An evolutionary age of 11.5 (1.5) Myr was obtained for IM Mon. Kinematical and dynamical analyses support the membership of the young thin-disk population system IM Mon to the On OB1a association dynamically. Finally, we derived the distance, age, and metallicity information of On OB1a sub-group using information of the IM Mon parameters.Öğe Updated MS Luminosity-Radius-Temperature-Mass Relations for Solar Neighborhood Galactic Disk Stars(Amer Inst Physics, 2018) Eker, Zeki; Bakis, Volkan; Bilir, Selcuk; Soydugan, Faruk; Steer, Ian; Soydugan, Esin; Bakis, HicranConventional mass- luminosity (M- L) relations are defined using 509 nearby main- sequence (MS) stars within the Solar neighborhood. A smooth mass- radius (M- R) relation was fixed from radii of MS stars appeared in literature having masses within the limits 0.179- 1.5 M. Similarly, a smooth mass- effective temperature (M- Teff) relation was derived for the main- sequence stars having masses within the limits 1.5- 31 M using their effective temperatures available. The omitted parts of M- R and M- Teff relations in the range from 0.179 to 31 M were computed according to Stephan- Boltzmann law, so inter- related M- L, M- R and M- Teff were achieved.
