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arXiv · 0805.3442

High resolution infrared spectra of NGC 6440 and NGC 6441: two massive Bulge Globular Clusters

L. Origlia·E. Valenti·R. M. Rich
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Abstract

Using the NIRSPEC spectrograph at Keck II, we have obtained infrared echelle spectra covering the 1.5-1.8 micron range for giant stars in the massive bulge globular clusters NGC6440 and NGC6441. We report the first high dispersion abundance for NGC6440, [Fe/H]=-0.56+/-0.02 and we find [Fe/H]=-0.50+/-0.02 for the blue HB cluster NGC6441. We measure an average $α$-enhancement of ~+0.3 dex in both clusters, consistent with previous measurements of other metal rich bulge clusters, and favoring 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 NGC6440 and NGC6441, respectively, and some Mg-Al anti-correlation in NGC6441. We also measure radial velocities vr=-76+/-3 km/s and vr=+14+/-3 km/s and velocity dispersions sigma=9+/-2 km/s and sigma=10+/-2 km/s, in NGC6440 and NGC6441, respectively.

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L. Origlia, E. Valenti, R. M. Rich. 2008-05-22. High resolution infrared spectra of NGC 6440 and NGC 6441: two massive Bulge Globular Clusters. https://doi.org/10.1111/j.1365-2966.2008.13492.x

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