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Nils Ryde

Nils Ryde

Professor

Nils Ryde

DETAILED ABUNDANCE ANALYSIS of A METAL-POOR GIANT in the GALACTIC CENTER

Author

  • N. Ryde
  • T. K. Fritz
  • R. M. Rich
  • B. Thorsbro
  • M. Schultheis
  • L. Origlia
  • S. Chatzopoulos

Summary, in English

We report the first results from our program to examine the metallicity distribution of the Milky Way nuclear star cluster connected to Sgr A∗, with the goal of inferring the star formation and enrichment history of this system, as well as its connection and relationship with the central 100 pc of the bulge/bar system. We present the first high-resolution (R ∼ 24,000), detailed abundance analysis of a K = 10.2 metal-poor, alpha-enhanced red giant projected at 1.5 pc from the Galactic center, using NIRSPEC on Keck II. A careful analysis of the dynamics and color of the star locates it at about pc line-of-sight distance in front of the nuclear cluster. It probably belongs to one of the nuclear components (cluster or disk), not to the bar/bulge or classical disk. A detailed spectroscopic synthesis, using a new line list in the K band, finds [Fe/H] ∼ -1.0 and [α/Fe] ∼ 0.4, consistent with stars of similar metallicity in the bulge. As known giants with comparable [Fe/H] and alpha enhancement are old, we conclude that this star is most likely to be a representative of the ∼10 Gyr old population. This is also the most metal-poor-confirmed red giant yet discovered in the vicinity of the nuclear cluster of the Galactic center. We consider recent reports in the literature of a surprisingly large number of metal-poor giants in the Galactic center, but the reported gravity of for these stars calls into question their reported metallicities.

Department/s

  • Lund Observatory

Publishing year

2016-11-01

Language

English

Publication/Series

Astrophysical Journal

Volume

831

Issue

1

Document type

Journal article

Publisher

American Astronomical Society

Topic

  • Astronomy, Astrophysics and Cosmology

Keywords

  • Galaxy: center
  • stars: abundances
  • stars: late-type

Status

Published

ISBN/ISSN/Other

  • ISSN: 0004-637X