### Yazar "Coskunoglu, B." seçeneğine göre listele

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Öğe Identification of field dwarfs and giants in the second Radial Velocity Experiment Data Release(Wiley-Blackwell, 2011) Bilir, S.; Karaali, S.; Ak, S.; Onal, O.; Coskunoglu, B.; Seabroke, G. M.Daha fazla The second Radial Velocity Experiment (RAVE) Data Release (DR2) derives log g values. However, we present a simpler and cleaner method of identifying dwarfs and giants by using only magnitudes, which does not require spectroscopic analysis. We confirm the method presented in an earlier paper, with which we estimate the number of dwarfs and giants using their positions in the JV two-magnitude diagram, by applying it to RAVE DR2. It is effective in estimating the number of dwarfs and giants at JH > 0.4 compared to RAVEs log g values. For JH= 0.4, where dwarfs and subgiants show a continuous transition in the J magnitude histogram, we used the Besancon Galaxy model predictions to statistically isolate giants. The percentages of giants for red stars and for the whole sample are 85 and 34 per cent, respectively. If we add the subgiants, the percentage of evolved stars for the whole sample increases to 59 per cent. For the first time in the literature, we have analysed the effect of CHISQ on RAVEs log g values (CHISQ is the penalized 2 from RAVEs technique of finding an optimal match between the observed spectrum and synthetic spectra to derive stellar parameters). Neither the CHISQ values nor the signal-to-noise ratio bias the RAVE log g values. Therefore, the method of identifying dwarfs and giants using the two-magnitude diagram has been verified against an unbiased data set.Daha fazla Öğe An Improved Metallicity Calibration with UBV Photometry(Csiro Publishing, 2011) Karaali, S.; Bilir, S.; Ak, S.; Yaz, E.; Coskunoglu, B.Daha fazla We used the data of 701 stars covering the colour index interval 0.32 < B - V <= 1.16, with metallicities -1.76 <= [Fe/H] <= +0.40 dex. The data were taken from the PASTEL catalogue and estimated metallicity-dependent guillotine factors, which provide a more accurate metallicity calibration. We reduced the metallicities of 11 different authors to the metallicities of Valenti & Fischer (2005), and thus obtained a homogeneous set of data which increased the accuracy of the calibration, i.e. [Fe/H] = -4.316d delta(2)(0.6) - 3.557 delta(0.6) + 0.105. Comparison of the metallicity residuals for two sets of data based on the metallicity-dependent guillotine factors with the ones obtained via metal-free guillotine factors shows that metallicities estimated by means of the new guillotine factors are more accurate than the other ones. This advantage can be used in the metallicity gradient investigation of the Galactic components, i.e. thin disc, thick disc, and halo.Daha fazla Öğe Local stellar kinematics from RAVE data - I. Local standard of rest(Oxford Univ Press, 2011) Coskunoglu, B.; Ak, S.; Bilir, S.; Karaali, S.; Yaz, E.; Gilmore, G.; Seabroke, G. M.Daha fazla We analyse a sample of 82 850 stars from the RAdial Velocity Experiment (RAVE) survey, with well-determined velocities and stellar parameters, to isolate a sample of 18 026 high-probability thin-disc dwarfs within 600 pc of the Sun. We derive space motions for these stars, and deduce the solar space velocity with respect to the local standard of rest. The peculiar solar motion we derive is in excellent agreement in radial U-circle dot and vertical W-circle dot peculiar motions with other recent determinations. Our derived tangential peculiar velocity, V-circle dot, agrees with very recent determinations, which favour values near 13 km s-1, in disagreement with earlier studies. The derived values are not significantly dependent on the comparison sample chosen, or on the method of analysis. The local Galaxy seems very well dynamically relaxed, in a near symmetric potential.Daha fazla Öğe Transformations between the 2MASS, SDSS, and BVI photometric systems for late-type giants(Wiley-V C H Verlag Gmbh, 2010) Yaz, E.; Bilir, S.; Karaali, S.; Ak, S.; Coskunoglu, B.; Cabrera-Lavers, A.Daha fazla We present colour transformations from Two Micron All Sky Survey (2MASS) photometric system to Johnson-Cousins system and to Sloan Digital Sky Survey (SDSS) system for late-type giants and vice versa. The giant star sample was formed using surface gravity constraints (2 < log g <= 3) to Cayrel de Strobel et al.'s (2001) spectroscopic catalogue. 2MASS, SDSS and Johnson-Cousins photometric data was taken from Cutri et al. (2003), Ofek (2008), and van Leeuwen (2007), respectively. The final sample was refined applying the following steps: (1) the data were dereddened, (2) the sample stars selected are of the highest photometric quality. We give two-colour dependent transformations as a function of metallicity as well as independent of metallicity. The transformations provide absolute magnitudes and distance determinations which can be used in space density evaluations at relatively short distances where some or all of the SDSS magnitudes of late-type giants are saturated. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, WeinheimDaha fazla Öğe Transformations between the WISE, 2MASS, SDSS and BVRI photometric systems - I. Transformation equations for dwarfs(Wiley-Blackwell, 2011) Bilir, S.; Karaali, S.; Ak, S.; Dagtekin, N. D.; Onal, O.; Yaz, E.; Coskunoglu, B.Daha fazla We present colour transformations for the conversion of the W1 and W2 magnitudes of the Wide-field Infrared Survey Explorer (WISE) photometric system to the Johnson-Cousins BVRI, Sloan Digital Sky Survey gri and Two-Micron All-Sky Survey JHK(s) photometric systems, for dwarfs. The W3 and W4 magnitudes were not considered due to their insufficient signal-to-noise ratio (S/N). The coordinates of 825 dwarfs along with their BVRI, gri and JHK(s) data taken from Bilir et al. were matched with the coordinates of stars in the preliminary data release of the WISE, and a homogeneous dwarf sample with high S/N had been obtained using the following constraints: (1) the data were dereddened; (2) giants were identified and excluded from the sample; (3) sample stars were selected according to data quality; (4) transformations were derived for subsamples of different metallicity ranges; and (5) transformations were two-colour-dependent. These colour transformations, coupled with known absolute magnitudes at shorter wavelengths, can be used in space-density evaluation for the Galactic (thin and thick) discs, at distances larger than the ones evaluated with JHK(s) photometry.Daha fazla