NGC 6558: A blue horizontal branch moderately metal-poor globular cluster in the bulge

B. Barbuy, M. Zoccali, S. Ortolani, D. Minniti, V. Hill, A. Renzini, E. Bica, A. Gómez

Resultado de la investigación: Article

32 Citas (Scopus)

Resumen

We present, for the first time, a detailed abundance analysis of five giant stars in the moderately metal-poor bulge globular cluster NGC 6558. Spectra have been obtained at the VLT with the multifiber spectrograph FLAMES in GIRAFFE mode (R ∼ 22,000). The resulting iron abundance is [Fe/H] = -0.97 ±0.15, in good agreement with the metallicity inferred from the slope of the red giant branch, but unusually high for a cluster with such a blue horizontal branch, possibly indicating an old age. A color-magnitude diagram in V and I, based on photometry obtained with the Wide-Field Imager at ESO, is also presented. An isochrone of 14 Gyr fits the evolutionary sequences, confirming an old age. NGC 6558 is another "second-parameter" bulge cluster. The metallicity derived is near the end of the low-metallicity tail of the bulge field-star distribution; hence, it presumably formed at the very early stages of the bulge formation, Abundance ratios show enhancements of the α-elements oxygen, magnesium, and silicon, with [O/Fe] = +0.38, [Mg/Fe] = +0.24, [Si/Fe] = +0.23, and solar calcium and titanium. The r-element europium is also enhanced by [Eu/Fe] = +0.36. The odd-Z elements sodium and aluminum, as well as the s-elements barium and lanthanum, show solar ratios. A heliocentric radial velocity of vrhel = -197.3 ±4 km s-1 is found for NGC 6558.

Idioma originalEnglish
Páginas (desde-hasta)1613-1625
Número de páginas13
PublicaciónAstronomical Journal
Volumen134
N.º4
DOI
EstadoPublished - 2007

Huella dactilar

globular clusters
metallicity
metal
metals
europium
giant stars
star distribution
color-magnitude diagram
barium
European Southern Observatory
lanthanum
radial velocity
titanium
silicon
spectrographs
photometry
magnesium
calcium
aluminum
diagram

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Citar esto

Barbuy, B., Zoccali, M., Ortolani, S., Minniti, D., Hill, V., Renzini, A., ... Gómez, A. (2007). NGC 6558: A blue horizontal branch moderately metal-poor globular cluster in the bulge. Astronomical Journal, 134(4), 1613-1625. https://doi.org/10.1086/521556
Barbuy, B. ; Zoccali, M. ; Ortolani, S. ; Minniti, D. ; Hill, V. ; Renzini, A. ; Bica, E. ; Gómez, A. / NGC 6558 : A blue horizontal branch moderately metal-poor globular cluster in the bulge. En: Astronomical Journal. 2007 ; Vol. 134, N.º 4. pp. 1613-1625.
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abstract = "We present, for the first time, a detailed abundance analysis of five giant stars in the moderately metal-poor bulge globular cluster NGC 6558. Spectra have been obtained at the VLT with the multifiber spectrograph FLAMES in GIRAFFE mode (R ∼ 22,000). The resulting iron abundance is [Fe/H] = -0.97 ±0.15, in good agreement with the metallicity inferred from the slope of the red giant branch, but unusually high for a cluster with such a blue horizontal branch, possibly indicating an old age. A color-magnitude diagram in V and I, based on photometry obtained with the Wide-Field Imager at ESO, is also presented. An isochrone of 14 Gyr fits the evolutionary sequences, confirming an old age. NGC 6558 is another {"}second-parameter{"} bulge cluster. The metallicity derived is near the end of the low-metallicity tail of the bulge field-star distribution; hence, it presumably formed at the very early stages of the bulge formation, Abundance ratios show enhancements of the α-elements oxygen, magnesium, and silicon, with [O/Fe] = +0.38, [Mg/Fe] = +0.24, [Si/Fe] = +0.23, and solar calcium and titanium. The r-element europium is also enhanced by [Eu/Fe] = +0.36. The odd-Z elements sodium and aluminum, as well as the s-elements barium and lanthanum, show solar ratios. A heliocentric radial velocity of vrhel = -197.3 ±4 km s-1 is found for NGC 6558.",
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Barbuy, B, Zoccali, M, Ortolani, S, Minniti, D, Hill, V, Renzini, A, Bica, E & Gómez, A 2007, 'NGC 6558: A blue horizontal branch moderately metal-poor globular cluster in the bulge', Astronomical Journal, vol. 134, n.º 4, pp. 1613-1625. https://doi.org/10.1086/521556

NGC 6558 : A blue horizontal branch moderately metal-poor globular cluster in the bulge. / Barbuy, B.; Zoccali, M.; Ortolani, S.; Minniti, D.; Hill, V.; Renzini, A.; Bica, E.; Gómez, A.

En: Astronomical Journal, Vol. 134, N.º 4, 2007, p. 1613-1625.

Resultado de la investigación: Article

TY - JOUR

T1 - NGC 6558

T2 - A blue horizontal branch moderately metal-poor globular cluster in the bulge

AU - Barbuy, B.

AU - Zoccali, M.

AU - Ortolani, S.

AU - Minniti, D.

AU - Hill, V.

AU - Renzini, A.

AU - Bica, E.

AU - Gómez, A.

PY - 2007

Y1 - 2007

N2 - We present, for the first time, a detailed abundance analysis of five giant stars in the moderately metal-poor bulge globular cluster NGC 6558. Spectra have been obtained at the VLT with the multifiber spectrograph FLAMES in GIRAFFE mode (R ∼ 22,000). The resulting iron abundance is [Fe/H] = -0.97 ±0.15, in good agreement with the metallicity inferred from the slope of the red giant branch, but unusually high for a cluster with such a blue horizontal branch, possibly indicating an old age. A color-magnitude diagram in V and I, based on photometry obtained with the Wide-Field Imager at ESO, is also presented. An isochrone of 14 Gyr fits the evolutionary sequences, confirming an old age. NGC 6558 is another "second-parameter" bulge cluster. The metallicity derived is near the end of the low-metallicity tail of the bulge field-star distribution; hence, it presumably formed at the very early stages of the bulge formation, Abundance ratios show enhancements of the α-elements oxygen, magnesium, and silicon, with [O/Fe] = +0.38, [Mg/Fe] = +0.24, [Si/Fe] = +0.23, and solar calcium and titanium. The r-element europium is also enhanced by [Eu/Fe] = +0.36. The odd-Z elements sodium and aluminum, as well as the s-elements barium and lanthanum, show solar ratios. A heliocentric radial velocity of vrhel = -197.3 ±4 km s-1 is found for NGC 6558.

AB - We present, for the first time, a detailed abundance analysis of five giant stars in the moderately metal-poor bulge globular cluster NGC 6558. Spectra have been obtained at the VLT with the multifiber spectrograph FLAMES in GIRAFFE mode (R ∼ 22,000). The resulting iron abundance is [Fe/H] = -0.97 ±0.15, in good agreement with the metallicity inferred from the slope of the red giant branch, but unusually high for a cluster with such a blue horizontal branch, possibly indicating an old age. A color-magnitude diagram in V and I, based on photometry obtained with the Wide-Field Imager at ESO, is also presented. An isochrone of 14 Gyr fits the evolutionary sequences, confirming an old age. NGC 6558 is another "second-parameter" bulge cluster. The metallicity derived is near the end of the low-metallicity tail of the bulge field-star distribution; hence, it presumably formed at the very early stages of the bulge formation, Abundance ratios show enhancements of the α-elements oxygen, magnesium, and silicon, with [O/Fe] = +0.38, [Mg/Fe] = +0.24, [Si/Fe] = +0.23, and solar calcium and titanium. The r-element europium is also enhanced by [Eu/Fe] = +0.36. The odd-Z elements sodium and aluminum, as well as the s-elements barium and lanthanum, show solar ratios. A heliocentric radial velocity of vrhel = -197.3 ±4 km s-1 is found for NGC 6558.

KW - Globular clusters: general

KW - Globular clusters: individual (NGC 6558)

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DO - 10.1086/521556

M3 - Article

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