Absolute Magnitude Calibration for Giants based on the Colour-Magnitude Diagrams of Galactic Clusters. II-Calibration with SDSS

TL;DR

This paper develops a calibration method for estimating the absolute magnitudes of red giant stars using SDSS data, based on their colour and metallicity, applicable to stars older than 2 Gyr.

Contribution

It introduces a new calibration for red giant absolute magnitudes using SDSS colours and metallicities, covering a wide range of metallicities and validated on multiple clusters.

Findings

Residuals mostly within -0.1 to 0.4 mag

Calibration applicable to stars older than 2 Gyr

Residual mean and std dev are 0.169 and 0.140 mag

Abstract

We present an absolute magnitude calibration for red giants with the colour magnitude diagrams of six Galactic clusters with different metallicities i.e. M92, M13, M3, M71, NGC 6791 and NGC 2158. The combination of the absolute magnitudes of the red giant sequences with the corresponding metallicities provides calibration for absolute magnitude estimation for red giants for a given $(g-r)_{0}$ colour. The calibration is defined in the colour interval 0.45 $\leq(g-r)_{0}\leq$ 1.30 mag and it covers the metallicity interval $-2.15\leq \lbrack Fe/H \rbrack \leq$ +0.37 dex. The absolute magnitude residuals obtained by the application of the procedure to another set of Galactic clusters lie in the interval $-0.28< \Delta M \leq +0.43$ mag. However, the range of 94% of the residuals is shorter, $-0.1<\Delta M \leq+0.4$ mag. The mean and the standard deviation of (all) residuals are 0.169 and 0.140 mag, respectively. The derived relations are applicable to stars older than 2 Gyr, the age of the youngest calibrating cluster.