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: Contribución a una revistaArtículo

33 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 originalInglés
Páginas (desde-hasta)1613-1625
Número de páginas13
PublicaciónAstronomical Journal
Volumen134
N.º4
DOI
EstadoPublicada - 2007

Áreas temáticas de ASJC Scopus

  • Astronomía y astrofísica
  • Ciencias planetarias y espacial

Huella Profundice en los temas de investigación de 'NGC 6558: A blue horizontal branch moderately metal-poor globular cluster in the bulge'. En conjunto forman una huella única.

  • Citar esto

    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, 134(4), 1613-1625. https://doi.org/10.1086/521556