The Relation between Near-Infrared Luminosity of RGB Bumps and Metallicity of Galactic Globular Clusters

Abstract

Using photometric data from the 2MASS second incremental release point source catalog we constructed Ks vs. (J-Ks) color-magnitude diagrams (CMDs) of Galactic globular clusters (GGCs) for which the JKs photometric data have been made available up to now. On the CMDs of 13 GGCs we identified RGB bump features and derived luminosities of bumps in Ks and in absolute Ks for 11 of them. We reconfirm the relation between abolute Ks magnitude of bump and metallicity [Fe/H]CG97 or [M/H] such that the luminosity of bump becomes brighter as metallicity [Fe/H]CG97 or [M/H] decreases. This result is similar to that obtained by Ferraro et al. (1999) for the relation between abolute V magnitude of bump and [M/H] based on observations of 47 GGCs which were conducted in the optical region (V vs. (B-V) CMDs). Our results show the same trend as those found by Ferraro et al. (2000) for the relations between abolute Ks magnitude of bump and metallicity [Fe/H]CG97 and [M/H] derived from observations of 8 GGCs in the same near-infrared (K vs. (J-K) CMDs). Combining with the data of Ferraro et al. (2000), we derive a robust relation for the metal-dependent luminosities of the bumps.