Journal Article

High resolution infrared spectra of NGC 6440 and NGC 6441:* two massive bulge globular clusters

L. Origlia, E. Valenti and R. M. Rich

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 388, issue 3, pages 1419-1425
Published in print August 2008 | ISSN: 0035-8711
Published online July 2008 | e-ISSN: 1365-2966 | DOI:
High resolution infrared spectra of NGC 6440 and NGC 6441:* two massive bulge globular clusters

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Using the NIRSPEC spectrograph at Keck II, we have obtained infrared echelle spectra covering the 1.5–1.8 μm range for giant stars in the massive bulge globular clusters NGC 6440 and NGC 6441. We report the first high-dispersion abundance for NGC 6440, [Fe/H]=−0.56 ± 0.02 and we find [Fe/H]=−0.50 ± 0.02 for the blue Horizontal Branch cluster NGC 6441. We measure an average α-enhancement of ≈+0.3 dex in both clusters, consistent with previous measurements of other metal rich bulge clusters, and favouring the scenario of a rapid-bulge formation and chemical enrichment. We also measure very low 12C/13C isotopic ratios (≈5 ± 1), suggesting that extra-mixing mechanisms are at work during evolution along the Red Giant Branch also in the high-metallicity regime. We also measure Al abundances, finding average [Al/Fe]= 0.45 ± 0.02 and [Al/Fe]= 0.52 ± 0.02 in NGC 6440 and 6441, respectively, and some Mg–Al anticorrelation in NGC 6441. We also measure radial velocities vr=−76 ± 3 and vr=+14 ± 3 km s−1 and velocity dispersions σ= 9 ± 2 and σ= 10 ± 2 km s−1 in NGC 6440 and 6441, respectively.

Keywords: techniques: spectroscopic; stars: abundances; stars: late-type; Galaxy: bulge; globular clusters: individual: NGC 6440; globular clusters: individual: NGC 6441

Journal Article.  3882 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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