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Chemical abundances for the outer halo cluster Pal 4 from co-added high-resolution spectroscopy

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Chemical abundances for the outer halo cluster Pal 4 from co-added high-resolution spectroscopy. / Koch, Andreas; Côté, P.
In: Astronomy and Astrophysics, Vol. 517, A59, 07.2010.

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Koch A, Côté P. Chemical abundances for the outer halo cluster Pal 4 from co-added high-resolution spectroscopy. Astronomy and Astrophysics. 2010 Jul;517:A59. doi: 10.1051/0004-6361/201014155

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@article{e2719888af154655bfbc0e6f00307483,
title = "Chemical abundances for the outer halo cluster Pal 4 from co-added high-resolution spectroscopy",
abstract = "Context. Chemical element abundances for distant Galactic globular clusters (GCs) hold important clues to the origin of the Milky Way halo and its substructures.Aims. We study the chemical composition of red giant stars in Pal 4 – one of the most remote GCs in the Milky Way – and compare our abundance measurements to those for both low surface brightness dwarf galaxies, and GCs in the inner and the outer halo.Methods. By co-adding high-resolution, low-S/N Keck/HIRES spectra of 19 stars along the red giant branch, we estimate chemical abundance ratios of 20 α-, iron peak-, and neutron-capture elements. Our method gives total uncertainties on most element-to-iron ratios of typically 0.2 dex.Results. We measure [Fe/H] = -1.41 ± 0.04 (statistical) ± 0.17 (systematic) and an α-enhancement of [α/Fe] = +0.38 ± 0.11 dex, which is consistent with the canonical value of ~+0.4 dex found for Galactic halo field stars and most halo GCs at this metallicity. Although Pal 4 has higher enhancements in the heavier elements with respect to the halo, the majority of the element ratios are, within the measurement errors, consistent with those for local halo field stars. We find, however, evidence for a lower [Mg/Ca] ratio than in other halo clusters.Conclusions. Based on the available evidence, we conclude that the material from which Pal 4 and the Galactic halo formed experienced similar enrichment processes, despite the apparently younger age of this cluster. Within the limitations of our methodology we find no significant indication of an iron spread, as is typical of genuine GCs of the Milky Way. However, abundance ratios for individual stars in Pal 4 and other distant satellites are urgently needed to understand the relationship, if any, between remote GCs and other halo substructures (i.e., luminous and ultra-faint dwarf spheroidal galaxies).",
author = "Andreas Koch and P. C{\^o}t{\'e}",
year = "2010",
month = jul,
doi = "10.1051/0004-6361/201014155",
language = "English",
volume = "517",
journal = "Astronomy and Astrophysics",
issn = "1432-0746",
publisher = "EDP Sciences",

}

RIS

TY - JOUR

T1 - Chemical abundances for the outer halo cluster Pal 4 from co-added high-resolution spectroscopy

AU - Koch, Andreas

AU - Côté, P.

PY - 2010/7

Y1 - 2010/7

N2 - Context. Chemical element abundances for distant Galactic globular clusters (GCs) hold important clues to the origin of the Milky Way halo and its substructures.Aims. We study the chemical composition of red giant stars in Pal 4 – one of the most remote GCs in the Milky Way – and compare our abundance measurements to those for both low surface brightness dwarf galaxies, and GCs in the inner and the outer halo.Methods. By co-adding high-resolution, low-S/N Keck/HIRES spectra of 19 stars along the red giant branch, we estimate chemical abundance ratios of 20 α-, iron peak-, and neutron-capture elements. Our method gives total uncertainties on most element-to-iron ratios of typically 0.2 dex.Results. We measure [Fe/H] = -1.41 ± 0.04 (statistical) ± 0.17 (systematic) and an α-enhancement of [α/Fe] = +0.38 ± 0.11 dex, which is consistent with the canonical value of ~+0.4 dex found for Galactic halo field stars and most halo GCs at this metallicity. Although Pal 4 has higher enhancements in the heavier elements with respect to the halo, the majority of the element ratios are, within the measurement errors, consistent with those for local halo field stars. We find, however, evidence for a lower [Mg/Ca] ratio than in other halo clusters.Conclusions. Based on the available evidence, we conclude that the material from which Pal 4 and the Galactic halo formed experienced similar enrichment processes, despite the apparently younger age of this cluster. Within the limitations of our methodology we find no significant indication of an iron spread, as is typical of genuine GCs of the Milky Way. However, abundance ratios for individual stars in Pal 4 and other distant satellites are urgently needed to understand the relationship, if any, between remote GCs and other halo substructures (i.e., luminous and ultra-faint dwarf spheroidal galaxies).

AB - Context. Chemical element abundances for distant Galactic globular clusters (GCs) hold important clues to the origin of the Milky Way halo and its substructures.Aims. We study the chemical composition of red giant stars in Pal 4 – one of the most remote GCs in the Milky Way – and compare our abundance measurements to those for both low surface brightness dwarf galaxies, and GCs in the inner and the outer halo.Methods. By co-adding high-resolution, low-S/N Keck/HIRES spectra of 19 stars along the red giant branch, we estimate chemical abundance ratios of 20 α-, iron peak-, and neutron-capture elements. Our method gives total uncertainties on most element-to-iron ratios of typically 0.2 dex.Results. We measure [Fe/H] = -1.41 ± 0.04 (statistical) ± 0.17 (systematic) and an α-enhancement of [α/Fe] = +0.38 ± 0.11 dex, which is consistent with the canonical value of ~+0.4 dex found for Galactic halo field stars and most halo GCs at this metallicity. Although Pal 4 has higher enhancements in the heavier elements with respect to the halo, the majority of the element ratios are, within the measurement errors, consistent with those for local halo field stars. We find, however, evidence for a lower [Mg/Ca] ratio than in other halo clusters.Conclusions. Based on the available evidence, we conclude that the material from which Pal 4 and the Galactic halo formed experienced similar enrichment processes, despite the apparently younger age of this cluster. Within the limitations of our methodology we find no significant indication of an iron spread, as is typical of genuine GCs of the Milky Way. However, abundance ratios for individual stars in Pal 4 and other distant satellites are urgently needed to understand the relationship, if any, between remote GCs and other halo substructures (i.e., luminous and ultra-faint dwarf spheroidal galaxies).

U2 - 10.1051/0004-6361/201014155

DO - 10.1051/0004-6361/201014155

M3 - Journal article

VL - 517

JO - Astronomy and Astrophysics

JF - Astronomy and Astrophysics

SN - 1432-0746

M1 - A59

ER -