Na-O anticorrelation and horizontal branches^*,**

VI. The chemical composition of the peculiar bulge globular cluster NGC 6388

¹ INAF – Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy e-mail: eugenio.carretta@oabo.inaf.it
² INAF – Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, 35122 Padova, Italy
³ Dpt. Cassiopée, UMR 6202, Observatoire de la Côte d'Azur, BP 4229, 06304 Nice Cedex 04, France
⁴ INAF – Osservatorio Astronomico di Collurania, via M. Maggini, 64100 Teramo, Italy
⁵ Observatoire de Paris, 61 avenue de l'Observatoire, 75014 Paris, France
⁶ European Southern Observatory, Alonso de Cordova 3107, Vitacura, Santiago, Chile
⁷ European Southern Observatory, Karl-Schwarzchild-Strasse 2, 85748 Garching bei Munchen, Germany

Received: 19 July 2006
Accepted: 22 December 2006

Abstract

We present the LTE abundance analysis of high resolution spectra for red giant stars in the peculiar bulge globular cluster NGC 6388. Spectra of seven members were taken using the UVES spectrograph at the ESO VLT2 and the multiobject FLAMES facility. We exclude any intrinsic metallicity spread in this cluster: on average,  dex on the scale of the present series of papers, where the first error bar refers to individual star-to-star errors and the second is systematic, relative to the cluster. Elements involved in H-burning at high temperatures show large spreads, exceeding the estimated errors in the analysis. In particular, the pairs Na and O, Al and Mg are anticorrelated and Na and Al are correlated among the giants in NGC 6388, the typical pattern observed in all galactic globular clusters studied so far. Stars in NGC 6388 shows an excess of process elements, similar to the one found in the twin bulge cluster NGC 6441. Mn is found underabundant in NGC 6388, in agreement with the average abundance ratio shown by clusters of any metallicity. Abundances of neutron-capture elements are homogeneously distributed within NGC 6388; the [Eu/Fe] ratio stands above the value found in field stars of similar metallicity.