A medium-resolution near-infrared spectral library of late-type stars. I.

We present an empirical infrared spectral library of medium-resolution (R approximate to 2000-3000) H (1.6 mum) and K (2.2 mum) band spectra of 218 red stars, spanning a range of [Fe/H] from similar to-2.2 to similar to+0.3. The sample includes Galactic disk stars, bulge stars from Baade's window, and red giants from Galactic globular clusters. We report the values of 19 indices covering 12 spectral features measured from the spectra in the library. Finally, we derive calibrations to estimate the effective temperature, and diagnostic relationships to determine the luminosity classes of individual stars from near-infrared spectra. This paper is part of a larger effort aimed at building a near-IR spectral library to be incorporated in population synthesis models, as well as at testing synthetic stellar spectra.