SDSS absolute magnitudes for thin–disc stars based on trigonometric parallaxes

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 (σπ/π≤ 0.05), metallicity (−0.30 ≤[M/H]≤ 0.20 dex), age (0 ≤t≤ 10 Gyr) and surface gravity (log g > 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 Mg 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.