The Peculiar Chemical Inventory of NGC 2419: an Extreme Outer Halo "Globular Cluster"
NGC 2419 is a massive outer halo Galactic globular cluster (GC) whose stars have previously been shown to have somewhat peculiar abundance patterns. We have observed seven luminous giants that are members of NGC 2419 with Keck/HIRES at reasonable signal-to-noise ratio. One of these giants is very peculiar, with an extremely low [Mg/Fe] and high [K/Fe] but normal abundances of most other elements. The abundance pattern does not match the nucleosynthetic yields of any supernova model. The other six stars show abundance ratios typical of inner halo Galactic GCs, represented here by a sample of giants in the nearby GC M30. Although our measurements show that NGC 2419 is unusual in some respects, its bulk properties do not provide compelling evidence for a difference between inner and outer halo GCs.
Additional Information© 2011 The American Astronomical Society. Received 2011 March 4; accepted 2011 July 12; published 2011 September 29. Based in part on observations obtained at the W. M. Keck Observatory, which is operated jointly by the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. We are grateful to the many people who have worked to make the Keck Telescope and its instruments a reality and to operate and maintain the Keck Observatory. The authors extend special thanks to those of Hawaiian ancestry on whose sacred mountain we are privileged to be guests. Without their generous hospitality, none of the observations presented herein would have been possible. We thank Alex Heger and Ken Nomoto for helpful conversations. J.G.C. and W.H. thank NSF grants AST-0507219 and AST-0908139 for partial support. Work by E.N.K. was supported by NASA through Hubble Fellowship grand HST-HF-01233.01 awarded to E.N.K. by the Space Telescope Science institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555.
Published - Cohen2011p16390Astrophys_J.pdf