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

Listeleniyor 1 - 2 / 2
  • Küçük Resim Yok
    Öğe
    Luminosity-colour relations for thin-disc main-sequence stars
    (Wiley-Blackwell, 2008) Bilir, S.; Karaali, S.; Ak, S.; Yaz, E.; Cabrera-Lavers, A.; Coskunoglu, K. B.
    In this study we present the absolute magnitude calibrations of thin-disc main-sequence stars in the optical (M(V)), and in the near-infrared (M(J)). Thin-disc stars are identified by means of Padova isochrones, and absolute magnitudes for the sample are evaluated via the newly reduced Hipparcos data. The obtained calibrations cover a large range of spectral types: from A0 to M4 in the optical and from A0 to M0 in the near-infrared. Also, we discuss the effects of binary stars and evolved stars on the absolute magnitude calibrations. The usage of these calibrations can be extended to the estimation of galactic model parameters for the thin disc individually, in order to compare these parameters with the corresponding ones estimated by X(min)(2) statistics (which provides galactic model parameters for thin and thick discs and halo simultaneously) to test any degeneracy between them. The calibrations can also be used in other astrophysical researches where distance plays an important role in that study.
  • Küçük Resim Yok
    Öğe
    SDSS absolute magnitudes for thin-disc stars based on trigonometric parallaxes
    (Wiley-Blackwell Publishing, Inc, 2009) Bilir, S.; Karaali, S.; Ak, S.; Coskunoglu, K. B.; Yaz, E.; Cabrera-Lavers, A.
    We present a new luminosity-colour relation based on trigonometric parallaxes for thin-disc main-sequence stars in Sloan Digital Sky Survey (SDSS) photometry. We matched stars from the newly reduced Hipparcos catalogue with the ones taken from Two-Micron All-Sky Survey (2MASS) All-Sky Catalogue of Point Sources, and applied a series of constraints, i.e. relative parallax errors (sigma pi/pi <= 0.05), metallicity (-0.30 <= [M/H] = 0.20 dex), age (0 <= t <= 10 Gyr) and surface gravity (logg > 4), and obtained a sample of thin-disc main-sequence stars. Then, we used our previous transformation equations (Bilir et al. 2008a) between SDSS and 2MASS photometries and calibrated the M(g) absolute magnitudes to the (g - r)(0) and (r - i)(0) colours. The transformation formulae between 2MASS and SDSS photometries along with the absolute magnitude calibration provide space densities for bright stars which saturate the SDSS magnitudes.