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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 CCD UBV and Gaia DR3 based analysis of NGC 189, NGC 1758 and NGC 7762 open clusters(Elsevier Sci Ltd, 2023) Yontan, Talar; Bilir, Selcuk; Cakmak, Hikmet; Raul, Michel; Banks, Timothy; Soydugan, Esin; Canbay, RemziyeThis paper presents photometric, astrometric, and kinematic analyses of the open clusters NGC 189, NGC 1758 and NGC 7762 based on CCD UBV photometric and Gaia Data Release 3 (DR3) data. According to membership analyses, we identified 32, 57 and 106 most probable member stars with membership probabilities P >= 0:5 in NGC 189, NGC 1758 and NGC 7762, respectively. The color excesses and photometric metallicities of each cluster were determined separately using UBV two-color diagrams. The color excess E(B - V) is 0: 590 +/- 0:023 mag for NGC 189, 0:310 +/- 0:022 mag for NGC 1758 and 0:640 +/- 0:017 mag for NGC 7762. The photometric metallicity [Fe/H] is -0:08 +/- 0:03 dex for both NGC 189 and NGC 1758, and -0:12 +/- 0:02 dex for NGC 7762. Distance moduli and ages of the clusters were obtained by comparing PARSEC isochrones with the color-magnitude diagrams constructed from UBV and Gaia photometric data. During this process, we kept as constant color excess and metallicity for each cluster. The estimated isochrone distance is 1201 +/- 53 pc for NGC 189, 902 +/- 33 pc for NGC 1758 and 911 +/- 31 pc for NGC 7762. These are compatible with the values obtained from trigonometric parallax. Ages of the clusters are 500 +/- 50 Myr, 650 +/- 50 Myr and 2000 +/- 200 Myr for NGC 189, NGC 1758 and NGC 7762, respectively. Galactic orbit integration of the clusters showed that NGC 1758 completely orbits outside the solar circle, while NGC 189 and NGC 7762 enter the solar circle during their orbits. (c) 2023 COSPAR. Published by Elsevier B.V. All rights reserved.Öğe Kepler Binary Stars in the NGC 6819 Open Cluster: KIC 5113146 and KIC 5111815(Iop Publishing Ltd, 2020) Soydugan, Esin; Alicavus, Fahri; Soydugan, Faruk; Bilir, SelcukIn this study, an investigation of two double-lined binary stars KIC 5113146 and KIC 5111815 in the NGC 6819 open cluster is presented based on both photometric and spectroscopic data. Simultaneous analysis of light and radial velocity curves was made and the absolute parameters of the systems' components were determined for the first time. We find that both systems have F-type main-sequence components. The masses and radii were found to be M-1 = 1.29 +/- 0.02M(circle dot), R-1 = 1.47 +/- 0.03 R-circle dot and M-2 = 1.19 +/- 0.02 M-circle dot, R-2 = 1.13 +/- 0.02 R-circle dot for the primary and secondary components of KIC 5113146; and M-1 = 1.51 +/- 0.08 M-circle dot, R-1 = 2.02 +/- 0.05 R-circle dot and M-2 = 1.19 +/- 0.07 M-circle dot, R-2 = 1.32 +/- 0.04 R-circle dot for the components of KIC 5111815, respectively. The evolutionary status of the components was evaluated based on the MESA evolutionary tracks and isochrones. The ages of KIC 5111815 and KIC 5113146 were derived to be about 2.50 +/- 0.35 Gyr and 1.95 +/- 0.40 Gyr, respectively. Photometric distances were calculated to be 2850 +/- 185 pc for KIC 5113146 and 3120 +/- 260 pc for KIC 5111815. The results reveal that both KIC 5113146 and KIC 5111815 systems are the most likely members of NGC 6819.Öğe Photometric and Kinematic Studies of Open Clusters Ruprecht 1 and Ruprecht 171(Wiley-V C H Verlag Gmbh, 2024) Cakmak, Hikmet; Yontan, Talar; Bilir, Selcuk; Banks, Timothy S.; Michel, Raul; Soydugan, Esin; Koc, SelizThis study outlines a detailed investigation using CCD UBV and Gaia DR3 data sets of the two open clusters Ruprecht 1 (Rup-1) and Ruprecht 171 (Rup-171). Fundamental astrophysical parameters such as color excesses, photometric metallicities, ages, and isochrone distances were based on UBV-data analyses, whereas membership probability calculations, structural and astrophysical parameters, as well as the kinematic analyses were based on Gaia DR3-data. We identified 74 and 596 stars as the most probable cluster members with membership probabilities over 50% for Rup-1 and Rup-171, respectively. The color excesses E(B-V) were obtained as 0.166 +/- 0.022 and 0.301 +/- 0.027 mag for Rup-1 and Rup-171, respectively. Photometric metallicity analyses were performed by considering F-G type main-sequence member stars and found to be [Fe/H]=-0.09 +/- 0.16 and [Fe/H]=-0.20 +/- 0.20 dex for Rup-1 and Rup-171, respectively. Ages and distances were based on both UBV and Gaia-data analyses; according to isochrone-fitting these values were estimated to be t=580 +/- 60 Myr, d=1469 +/- 57 pc for Rup-1 and t=2700 +/- 200 Myr, d=1509 +/- 69 pc for Rup-171. The present-day mass function slope of Rup-1 was estimated as 1.26 +/- 0.32 and Rup-171 as 1.53 +/- 1.49. Galactic orbit integration analyses showed that both of the clusters might be formed outside the solar circle.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 absolute parameters and kinematics of IS CMa(Wiley-V C H Verlag Gmbh, 2024) Evcil, Serkan; Adalali, Simge; Alan, Neslihan; Canbay, Remziye; Bilir, SelcukEclipsing binary systems are significant objects for astrophysics in that direct observations can determine the fundamental parameters of stars. In this study, we precisely determined the fundamental parameters of the binary component stars obtained by simultaneous analysis of radial velocities and the TESS light curve using the Wilson and Devinney code. Following the analysis, the masses and radii of the primary and secondary components were determined as M1 = 1.58 +/- 0.01M(circle dot), M-2 = 0.48 +/- 0.02M(circle dot), and R-1 = 1.93 +/- 0.01R(circle dot), R-2 = 1.14 +/- 0.01R(circle dot), respectively. Furthermore, the distance of IS CMa is calculated as 92.7 +/- 6.5$$ 92.7\pm 6.5 $$ pc. On the basis of the analysis of the mid-eclipse times, it was found that the variation in the orbital period is represented by an upward parabola. It has an increasing rate of dP/dt = 1.09 x 10(-7). Using PARSEC stellar evolutionary tracks and isochrones with solar metallicity estimated the age of IS CMa as 1.3 +/- 0.1 Gyr. Kinematic and Galactic orbital parameters of IS CMa were obtained from the astrometric and spectroscopic data of the system. The Galactic orbit analysis reveals that IS CMa formed inside the solar circle and it is a member of the young thin-disc population.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.
