Near-IR features in late type stars : their relation with stellar atmosphere parameters.

CCD spectroscopic observations for a sample of 106 late type stars plus three galactic globular clusters in the near-IR are presented. The most prominent features in that spectral region, the IR Ca-II triplet (8498, 8542, 8662A) and the Mg-I line at 8807 A, are measured and their dependence on the stellar atmosphere parameters (surface gravity, effective temperature and metal content) is analyzed. In agreement with what is found in previous studies, the Ca-II triplet strength shows biparametrical behavior with surface gravity and metal abundance. The IR Mg-I line strength is also biparametric, depending mainly on metal abundance and effective temperature. Principal component analysis techniques allow the prediction of the metal abundance and surface gravity as a function of three observables: the IR Ca-II triplet strength, the strength of the IR Mg-I line and the (R-I) color.