Absolute Magnitude Calibration for Dwarfs Based on the Colour-Magnitude Diagrams of Galactic Clusters

Abstract

We present two absolute magnitude calibrations for dwarfs based on colour-magnitude diagrams of Galactic clusters. The combination of the M-g absolute magnitudes of the dwarf fiducial sequences of the clusters M92, M13, M5, NGC 2420, M67, and NGC 6791 with the corresponding metallicities provides absolute magnitude calibration for a given (g - r)(0) colour. The calibration is defined in the colour interval 0.25 = -0.002 and sigma = 0.065 mag, respectively. The calibration of the M-J absolute magnitude in terms of metallicity is carried out by using the fiducial sequences of the clusters M92, M13, 47 Tuc, NGC 2158, and NGC 6791. It is defined in the colour interval 0.90 = 0.05 and sigma = 0.13 mag, respectively. The derived relations are applicable to stars older than 4 Gyr for the M-g calibration, and older than 2 Gyr for the M-J calibration. The cited limits are the ages of the youngest calibration clusters in the two systems.