SIMBAD references

Based on Beijing-Arizona–Taiwan–Connecticut (BATC) and Sloan Digital Sky Survey (SDSS) photometric data, we adopt the spectral energy distribution (SED) fitting method to evaluate the metallicity distribution for ∼40 000 main-sequence stars in the Galaxy. According to the derived photometric metallicities of these sample stars, we find that the metallicity distribution shifts from metal-rich to metal-poor with the increase of distance from the Galactic Centre. The mean metallicity is about -1.5±0.2 dex in the outer halo and -1.3±0.1 dex in the inner halo and smoothly decreases from -0.4 to -0.8 in the interval 0 < r ≤ 5 kpc. A fluctuation in mean metallicity with Galactic longitude can be found in the interval 4 < r ≤ 8 kpc. There is a vertical abundance gradient d[Fe/H]/dz∼-0.21±0.05 dex/kpc for the thin disc (z ≤ 2 kpc). At a distance 2 < z ≤ 5 kpc, where thick-disc stars dominate, the gradient is about -0.16 ±0.06 dex/kpc; this can be interpreted as a mixture of stellar populations with different mean metallicities at all z levels. The vertical metallicity gradient is -0.05±0.04 dex/kpc for the halo (z > 5 kpc), so there is little or no metallicity gradient in the halo.