Yazar "Onal, O." seçeneğine göre listele

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    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.
    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.
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    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.
    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.