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

Thorsbro, B. LU ; Ryde, N. LU ; Schultheis, M.; Hartman, H. LU ; Rich, R. M.; Lomaeva, M.; Origlia, L. and Jönsson, H. LU (2018) In Astrophysical Journal 866(1).
Abstract

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... (More)

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.

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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Galaxy: center, stars: abundances, stars: late-type
in
Astrophysical Journal
volume
866
issue
1
publisher
American Astronomical Society
external identifiers
  • scopus:85055277235
ISSN
0004-637X
DOI
10.3847/1538-4357/aadb97
language
English
LU publication?
yes
id
9bcb44a0-bc0a-4a60-bf77-e8316a305e90
date added to LUP
2018-11-15 14:37:38
date last changed
2019-03-19 04:02:32
@article{9bcb44a0-bc0a-4a60-bf77-e8316a305e90,
  abstract     = {<p>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.</p>},
  articleno    = {52},
  author       = {Thorsbro, B. and Ryde, N. and Schultheis, M. and Hartman, H. and Rich, R. M. and Lomaeva, M. and Origlia, L. and Jönsson, H.},
  issn         = {0004-637X},
  keyword      = {Galaxy: center,stars: abundances,stars: late-type},
  language     = {eng},
  number       = {1},
  publisher    = {American Astronomical Society},
  series       = {Astrophysical Journal},
  title        = {Evidence against Anomalous Compositions for Giants in the Galactic Nuclear Star Cluster},
  url          = {http://dx.doi.org/10.3847/1538-4357/aadb97},
  volume       = {866},
  year         = {2018},
}