The Relation between Near-infrared Luminosity of Red Giant Branch Bumps and Metallicity of Galactic Globular Clusters

Abstract

Using photometric data from the Two Micron All Sky Survey Second Incremental Release Point Source Catalog, we constructed Ks versus 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 red giant branch bump features and derived luminosities of bumps in Ks (K) and in M (M) for 11 of them. We reconfirm the relation between M 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. (published in 1999) for the relation between M and [M/H] based on observations of 47 GGCs that were conducted in the optical region (V vs. B-V CMDs). Our results show the same trend as those found by Ferraro et al. (published in 2000) for the relations between M and metallicity [Fe/H]CG97 and [M/H] derived from observations of eight GGCs in the same near-infrared region (K vs. J-K CMDs). Combining with the 2000 data of Ferraro et al., we derive a robust relation for the metal-dependent luminosities of the bumps.