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

TL;DR

This paper develops a calibration method for estimating the [$eta/$Fe] element in dwarf stars using SDSS photometry, enabling large-scale Galactic chemical analysis up to 9 kpc from the plane.

Contribution

It introduces a new polynomial calibration for [$eta/$Fe] based on ultraviolet excess, applicable to a broad sample of dwarf stars with high accuracy.

Findings

Detected a positive [$eta/$Fe] gradient with height up to 5 kpc.

Calibrated [$eta/$Fe] for over 23,000 stars in a high-latitude field.

Found a flat [$eta/$Fe] distribution beyond 5 kpc.

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.