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

References in corpus (8)

• The Victoria-Regina Stellar Models: Evolutionary Tracks and Isochrones for a Wide Range in Mass and Metallicity that Allow for Empirically Constrained Amounts of Convective Core Overshooting
• A consistent explanation for ${}^{12}$C/${}^{13}$C, ${}^7$Li, and ${}^3$He anomalies in red giant stars
• Helium variation due to self-pollution among Globular Cluster stars: consequences on the horizontal branch morphology
• Abundances of C, N, O in slightly evolved stars in the globular clusters NGC 6397, NGC 6752 and 47 Tuc
• C and N Abundances in Stars At the Base of the Red Giant Branch in M5
• Calibration of the CH and CN Variations Among Main Sequence Stars in M71 and in M13
• Light Element Abundance Inhomogeneities in Globular Clusters: Probing Star Formation and Evolution in the Early Milky Way
• CN Variations in NGC 7006

Cited by in corpus (25)

• Multiple populations in globular clusters. Lessons learned from the Milky Way globular clusters
• Formation and Dynamical Evolution of Multiple Stellar Generations in Globular Clusters
• The Ages of 55 Globular Clusters as Determined Using an Improved delta V_TO^HB Method Along with Color-Magnitude Diagram Constraints, and Their Implications for Broader Issues
• Building the Galactic halo from globular clusters: evidence from chemically unusual red giants
• The fraction of second generation stars in Globular Clusters from the analysis of the Horizontal Branch
• Mining SDSS in search of Multiple Populations in Globular Clusters
• Light-element Abundance Variations in the Milky Way Halo
• Carbon in Red Giants in Globular Clusters and Dwarf Spheroidal Galaxies
• Deep Mixing and Metallicity: Carbon Depletion in Globular Cluster Giants
• The Role of Thermohaline Mixing in Intermediate- and Low-Metallicity Globular Clusters
• A Survey of CN and CH Variations in Galactic Globular Clusters from SDSS Spectroscopy
• In search of massive single-population Globular Clusters
• Chemical abundances in the globular clusters NGC 5024 and NGC 5466 from optical and infrared spectroscopy
• Evidence for multiple populations in the massive globular cluster NGC 2419 from deep uVI LBT photometry
• Carbon and nitrogen abundances of individual stars in the Sculptor dwarf spheroidal galaxy
• ESO452-SC11: The lowest mass globular cluster with a potential chemical inhomogeneity
• Light-Element Abundance Variations at Low Metallicity: the Globular Cluster NGC 5466
• Kron 3: a fourth intermediate age cluster in the SMC with evidence of multiple populations
• A broad perspective on multiple abundance populations in the globular cluster NGC 1851
• Carbon and nitrogen abundances of stellar populations in the globular cluster M 2
• The Pristine survey -- XV. A CFHT ESPaDOnS view on the Milky Way halo and disc populations
• An Improved Bandstrength Index for the CH G Band of Globular Cluster Giants
• Cyanogen in NGC 1851 RGB and AGB Stars: Quadrimodal Distributions
• The CN-CH positive correlation in the globular cluster NGC 5286
• Evidence for C and Mg variations in the GD-1 stellar stream