THE BIZARRE CHEMICAL INVENTORY OF NGC 2419, AN EXTREME OUTER HALO GLOBULAR CLUSTER

Cohen, Judith G

doi:10.1088/0004-637X/760/1/86

Title: THE BIZARRE CHEMICAL INVENTORY OF NGC 2419, AN EXTREME OUTER HALO GLOBULAR CLUSTER

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Abstract

We present new Keck/HIRES observations of six red giants in the globular cluster (GC) NGC 2419. Although the cluster is among the most distant and most luminous in the Milky Way, it was considered chemically ordinary until very recently. Our previous work showed that the near-infrared Ca II triplet line strength varied more than expected for a chemically homogeneous cluster, and that at least one star had unusual abundances of Mg and K. Here, we confirm that NGC 2419 harbors a population of stars, comprising about one-third of its mass, that is depleted in Mg by a factor of eight and enhanced in K by a factor of six with respect to the Mg-normal population. Although the majority, Mg-normal population appears to have a chemical abundance pattern indistinguishable from ordinary, inner-halo GCs, the Mg-poor population exhibits dispersions of several elements. The abundances of K and Sc are strongly anti-correlated with Mg, and some other elements (Si and Ca among others) are weakly anti-correlated with Mg. These abundance patterns suggest that the different populations of NGC 2419 sample the ejecta of diverse supernovae in addition to asymptotic giant branch ejecta. However, the abundances of Fe-peak elements except Sc show no star-to-starmore »« less

Authors:: Cohen, Judith G

Publication Date:: Tue Nov 20 00:00:00 EST 2012

OSTI Identifier:: 22086284

Resource Type:: Journal Article

Journal Name:: Astrophysical Journal

Additional Journal Information:: Journal Volume: 760; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0004-637X

Country of Publication:: United States

Language:: English

Subject:: 79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ASTRONOMY; ASTROPHYSICS; ASYMPTOTIC SOLUTIONS; CALCIUM; CALCIUM IONS; ELEMENT ABUNDANCE; MAGNESIUM; MILKY WAY; POTASSIUM; SILICON; STAR CLUSTERS; SUPERNOVAE; TRIPLETS; VARIATIONS

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                    Cohen, Judith G, and Kirby, Evan N., E-mail: jlc@astro.caltech.edu, E-mail: enk@astro.caltech.edu. THE BIZARRE CHEMICAL INVENTORY OF NGC 2419, AN EXTREME OUTER HALO GLOBULAR CLUSTER.  United States: N. p., 2012. 
        Web.  doi:10.1088/0004-637X/760/1/86.

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                    Cohen, Judith G, & Kirby, Evan N., E-mail: jlc@astro.caltech.edu, E-mail: enk@astro.caltech.edu. THE BIZARRE CHEMICAL INVENTORY OF NGC 2419, AN EXTREME OUTER HALO GLOBULAR CLUSTER.  United States.  https://doi.org/10.1088/0004-637X/760/1/86

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                    Cohen, Judith G, and Kirby, Evan N., E-mail: jlc@astro.caltech.edu, E-mail: enk@astro.caltech.edu. 2012.  
        "THE BIZARRE CHEMICAL INVENTORY OF NGC 2419, AN EXTREME OUTER HALO GLOBULAR CLUSTER".  United States.  https://doi.org/10.1088/0004-637X/760/1/86.

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@article{osti_22086284,

  title        = {THE BIZARRE CHEMICAL INVENTORY OF NGC 2419, AN EXTREME OUTER HALO GLOBULAR CLUSTER},

  author       = {Cohen, Judith G and Kirby, Evan N., E-mail: jlc@astro.caltech.edu, E-mail: enk@astro.caltech.edu},

  abstractNote = {We present new Keck/HIRES observations of six red giants in the globular cluster (GC) NGC 2419. Although the cluster is among the most distant and most luminous in the Milky Way, it was considered chemically ordinary until very recently. Our previous work showed that the near-infrared Ca II triplet line strength varied more than expected for a chemically homogeneous cluster, and that at least one star had unusual abundances of Mg and K. Here, we confirm that NGC 2419 harbors a population of stars, comprising about one-third of its mass, that is depleted in Mg by a factor of eight and enhanced in K by a factor of six with respect to the Mg-normal population. Although the majority, Mg-normal population appears to have a chemical abundance pattern indistinguishable from ordinary, inner-halo GCs, the Mg-poor population exhibits dispersions of several elements. The abundances of K and Sc are strongly anti-correlated with Mg, and some other elements (Si and Ca among others) are weakly anti-correlated with Mg. These abundance patterns suggest that the different populations of NGC 2419 sample the ejecta of diverse supernovae in addition to asymptotic giant branch ejecta. However, the abundances of Fe-peak elements except Sc show no star-to-star variation. We find no nucleosynthetic source that satisfactorily explains all of the abundance variations in this cluster. Because NGC 2419 appears like no other GC, we reiterate our previous suggestion that it is not a GC at all, but rather the core of an accreted dwarf galaxy.},

  doi          = {10.1088/0004-637X/760/1/86},

  url          = {https://www.osti.gov/biblio/22086284},
  journal      = {Astrophysical Journal},

  issn         = {0004-637X},

  number       = 1,

  volume       = 760,

  place        = {United States},

  year         = {Tue Nov 20 00:00:00 EST 2012},

  month        = {Tue Nov 20 00:00:00 EST 2012}

}

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