Photometric Calibration of the $[\alpha /$Fe] Element: II. Calibration with SDSS Photometry

Abstract

We present the calibration of the [$\alpha /$Fe] element in terms of ultra-violet excess for 465 dwarf stars with spectral type F0-K2. We used a single calibration, fitted to a third degree polynomial with a square of the correlation coefficient 0.74 and standard deviation 0.05 mag, for all stars due to their small colour range, $0.1<(g-r{)}_0\le 0.6$ mag, and high frequency in the blueward of the spectrum which minimize the guillotine effect. Our calibration provides [$\alpha /$Fe] elements in the range $(-0.05,0.35]$ dex. We applied the procedure to a high-latitude field, $85^{\circ }\le b\le 90^{\circ }$ with size 78 deg${}^2$ and we could estimate the [$\alpha /$Fe] elements of 23,414 dwarf stars which occupy a Galactic region up to a vertical distance of $z=9$ kpc. We could detect a small positive gradient, $d[\alpha /\mathrm{Fe}]/dz=+0.032\pm 0.002$ dex kpc${}^{-1}$, for the range $0<z<5$ kpc, while the distribution of the [$\alpha /$Fe] element is flat for further $z$ distances.

9 pages amd 8 figures, accepted for publication in Astrophysics and Space Science

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