Journal
ASTRONOMICAL JOURNAL
Volume 123, Issue 3, Pages 1559-1569Publisher
IOP PUBLISHING LTD
DOI: 10.1086/338897
Keywords
Galaxy : bulge; globular clusters : individual (Liller 1, NGC 6553); stars : abundances; stars : late-type; techniques : spectroscopic
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Using the NIRSPEC spectrograph at Keck II, we have obtained echelle spectra covering the range 1.5-1.8 l m for two of the brightest giants in Liller 1 and NGC 6553, old metal-rich globular clusters in the Galactic bulge. We use spectrum synthesis for the abundance analysis and find [Fe=H] = -0.3 +/- 0.2 and [O=H] = 0.3 +/- 0.1 ( from the OH lines) for the giants in both clusters. We measure strong lines for the alpha-elements Mg, Ca, and Si, but the lower sensitivity of these lines to abundance permits us only to state a general [alpha/Fe] = 0.3 +/- 0.2 dex. The composition of the clusters is similar to that of field stars in the bulge and is consistent with a scenario in which the clusters formed early, with rapid enrichment. We have difficulty achieving a good fit to the spectrum of NGC 6553 using either the low or the high values recently reported in the literature, unless unusually large or no alpha-element enhancements are adopted, respectively.
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