NGC 6558 : a blue horizontal branch moderately metal-poor globular cluster in the bulge
![Thumbnail](/bitstream/handle/10183/108242/000625421.pdf.jpg?sequence=3&isAllowed=y)
Visualizar/abrir
Data
2007Autor
Tipo
Assunto
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- ...
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 Vand 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 showenhancements of the -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 vr hel = −197.3 ±4 km s-ˡ is found for NGC 6558. ...
Contido em
The astronomical journal. Vol. 134, no. 4 (Oct. 2007), p. 1613-1625
Origem
Estrangeiro
Coleções
-
Artigos de Periódicos (39541)Ciências Exatas e da Terra (6036)
Este item está licenciado na Creative Commons License
![](/themes/Mirage2Novo//images/lume/cc.png)