Absolute Magnitude Calibration for Red Giants based on the Colour-Magnitude Diagrams of Galactic Clusters. III-Calibration with 2MASS

TL;DR

This paper develops new calibrations for absolute magnitudes of red giants using 2MASS data and cluster colour-magnitude diagrams, covering various metallicities and applicable to stars older than 4 Gyr.

Contribution

It introduces two new absolute magnitude calibrations for red giants based on 2MASS colours and cluster data, extending previous work to a broader metallicity range.

Findings

Calibrations cover metallicities from -2.15 to +0.37 dex.

Residuals are within approximately ±0.3 mag.

Applicable to stars older than 4 Gyr.

Abstract

We present two absolute magnitude calibrations, $M_{J}$ and $M_{K_s}$, for red giants with the colour magnitude diagrams of five Galactic clusters with different metallicities i.e. M92, M13, M71, M67, and NGC 6791. 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 colour. The calibrations for $M_{J}$ and $M_{K_s}$ are defined in the colour intervals $1.3\leq(V-J)_{0}\leq2.8$ and $1.75 \leq (V-K_{s})_{0}\leq 3.80$ mag, respectively, and they cover 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 intervals $-0.08<\Delta M_{J}\leq +0.34$ and $-0.10< \Delta M_{K_s}\leq +0.27$ mag for $M_{J}$ and $M_{K_s}$, respectively. The means and standard deviations of the residuals are $<\Delta M_{J}>= 0.137$ and $\sigma_{M_J}=0.080$, and $<\Delta M_{K_s}>=0.109$ and $\sigma_{M_{K_{s}}}=0.123$ mag. The derived relations are applicable to stars older than 4 Gyr, the age of the youngest calibrating cluster.