2000A&A...361...92C

High-resolution echelle spectra of five giants and eleven subgiants of the metal-poor globular cluster NGC 6397 were obtained at the ESO 3.5m (NTT) and 3.6m telescopes. A detailed analysis of the 16 sample stars was carried out, providing atmospheric parameters (T_eff, log g, [Fe/H], v_t) and element abundances. The metallicity of the cluster is [Fe/H]=-2.0 with a r.m.s. of ±0.05, irrespective of the position in the Colour - Magnitude Diagram, with no variations as a function of effective temperatures and gravities. The dispersion in metal abundance, obtained over a range of 5 magnitudes and 1400K, is negligible and well within the measurement uncertainties. α-elements are mildly overabundant while the s-elements are deficient relative to iron by about 0.2dex. [O/Fe] is also mildly overabundant for the two stars where the line is detected. The Li abundances in the present sample and those of turnoff stars by Pasquini and Molaro (1996A&A...307..761P) are complementary in terms of evolutionary stage. The Li abundances decrease off the main sequence along the red giant branch, confirming that extra depletion must occur for stars cooler than ∼5000K and V brighter than ∼14.