Metallicity calibration and photometric parallax estimation: II. SDSS photometry

Abstract

We used the updated [Fe/H] abundances of 168 F-G type dwarfs and calibrated them to a third order polynomial in terms of reduced ultraviolet excess, δ0.41 defined with ugr data in the SDSS. We estimated the Mg absolute magnitudes for the same stars via the re-reduced Hipparcos parallaxes and calibrated the absolute magnitude offsets, ΔMg, relative to the intrinsic sequence of Hyades to a third order polynomial in terms of δ0.41. The ranges of the calibrations are ‑2<[Fe/H]≤0.3dex and 4<Mg≤6mag. The mean of the residuals and the corresponding standard deviation for the metallicity calibration are 0 and 0.137 mag; while, for the absolute magnitude calibration they are 0 and 0.179 mag, respectively. We applied our procedures to 23,414 dwarf stars in the Galactic field with the Galactic coordinates 85∘≤b≤90∘, 0∘≤l≤360∘ and size 78 deg². We estimated absolute magnitude Mg dependent vertical metallicity gradients as a function of vertical distance Z. The gradients are deep in the range of 0<Z≤5kpc, while they are very small positive numbers beyond Z=5kpc. All dwarfs with 5<Mg≤6mag are thin-disc stars and their distribution shows a mode at (g‑r)0≈0.38mag, while the absolute magnitudes 4<Mg≤5 are dominated by thick disc and halo stars, i.e. the apparently bright ones (g0≤18mag) are thick-disc stars with a mode at (g‑r)0∼0.38mag, while the halo population is significant in the faint stars (g0>18mag).