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Nils Ryde

Nils Ryde

Professor

Nils Ryde

Evidence against Anomalous Compositions for Giants in the Galactic Nuclear Star Cluster

Author

  • B. Thorsbro
  • N. Ryde
  • M. Schultheis
  • H. Hartman
  • R. M. Rich
  • M. Lomaeva
  • L. Origlia
  • H. Jönsson

Summary, in English

Very strong Sc i lines have recently been found in cool M giants in the Nuclear Star Cluster (NSC) in the Galactic center. Interpreting these as anomalously high scandium abundances in the Galactic center would imply a unique enhancement signature and chemical evolution history for NSCs, and a potential test for models of chemical enrichment in these objects. We present high resolution K-band spectra (NIRSPEC/Keck II) of cool M giants situated in the solar neighborhood and compare them with spectra of M giants in the NSC. We clearly identify strong Sc i lines in our solar neighborhood sample as well as in the NSC sample. The strong Sc i lines in M giants are therefore not unique to stars in the NSC and we argue that the strong lines are a property of the line formation process that currently escapes accurate theoretical modeling. We further conclude that for giant stars with effective temperatures below approximately 3800 K these Sc i lines should not be used for deriving the scandium abundances in any astrophysical environment until we better understand how these lines are formed. We also discuss the lines of vanadium, titanium, and yttrium identified in the spectra, which demonstrate a similar striking increase in strength below 3500 K effective temperature.

Department/s

  • Lund Observatory

Publishing year

2018

Language

English

Publication/Series

Astrophysical Journal

Volume

866

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