CN Bimodality at Low Metallicity: The Globular Cluster M53

Abstract

We present low resolution UV-blue spectroscopic observations of red giant stars in the globular cluster M53 ([Fe/H]=-1.84), obtained to study primordial abundance variations and deep mixing via the CN and CH absorption bands. The metallicity of M53 makes it an attractive target: a bimodal distribution of 3883 angstrom CN bandstrength is common in moderate- and high-metallicity globular clusters ([Fe/H] > -1.6) but unusual in those of lower metallicity ([Fe/H] < -2.0). We find that M53 is an intermediate case, and has a broad but not strongly bimodal distribution of CN bandstrength, with CN and CH bandstrengths anticorrelated in the less-evolved stars. Like many other globular clusters, M53 also exhibits a general decline in CH bandstrength and [C/Fe] abundance with rising luminosity on the red giant branch.

8 pages including 11 figures and 1 table, accepted by PASP

Cited by in corpus (4)

• Formation and Dynamical Evolution of Multiple Stellar Generations in Globular Clusters
• The fraction of second generation stars in Globular Clusters from the analysis of the Horizontal Branch
• Deep Mixing and Metallicity: Carbon Depletion in Globular Cluster Giants
• An Improved Bandstrength Index for the CH G Band of Globular Cluster Giants