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, \(0.1<(g-r)_0\leq 0.6\) 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, \(85^\circ \leq b \leq 90^\circ\) 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, \(d[\alpha/{\rm Fe}]/dz=+0.032 \pm0.002\) dex kpc\(^{-1}\), for the range \(0<z<5\) kpc, while the distribution of the [\(\alpha/\)Fe] element is flat for further \(z\) distances.