Photometric calibration of the [ α $\alpha$ /Fe] element: II. Calibration with SDSS photometry

Abstract

We present the calibration of the [α/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 ≤ 0.6 mag, and high frequency in the blueward of the spectrum which minimize the guillotine effect. Our calibration provides [α/Fe] elements in the range (−0.05, 0.35] dex. We applied the procedure to a high-latitude field, 85• ≤ b ≤ 90• with size 78 deg 2 and we could estimate the [α/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[α/Fe]/dz = +0.032 ± 0.002 dex kpc −1 , for the range 0 < z < 5 kpc, while the distribution of the [α/Fe] element is flat for further z distances.

On the Origin of Metal-poor Stars in the Solar Neighborhood

“…In addition, discovery of several halo substructures (Grillmair 2006;Sesar et al 2007;Belokurov et al 2007;Kepley et al 2007;Klement 2010;Helmi et al 2017;Li et al 2019) in the literature also requires up-to-date stellar abundances for halo stars. However, an almost distinct abundance pattern in α-elements is present for the thin and the thick disk member of the Galaxy (Bensby et al 2003(Bensby et al , 2005(Bensby et al , 2014Reddy et al 2003Reddy et al , 2006Nissen & Schuster 2011;Adibekyan et al 2012;Karaali et al 2016Karaali et al , 2019Yaz Gökçe et al 2017;Plevne et al 2020). The latter group tend to be slightly metal-poor but have enhanced α-element abundances.…”