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arXiv · 0710.5759

CN Bimodality at Low Metallicity: The Globular Cluster M53

Sarah L. Martell·Graeme H. Smith·Michael M. Briley
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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.

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Sarah L. Martell, Graeme H. Smith, Michael M. Briley. 2007-10-30. CN Bimodality at Low Metallicity: The Globular Cluster M53. https://doi.org/10.1086/525060

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