Abstract details

Stellar population synthesis models are crucial for the understanding of the large amount of data which is being gathered for galaxies at low and high redshift, and provide the only way to compare the ``real world'' with the theoretical framework. The best models require extensive empirical stellar spectral libraries, which at present are starting to be quite complete in the optical range. However the situation is different in the near-infrared, which observational windows have been, until recently, poorly exploited specially due to the lack of appropriate instrumentation. Here we present the results of an observational program aimed to overcome this problem and to provide a stellar library in the K band with the required coverage of physical stellar parameters: effective temperature, gravity, metallicity and non-solar abundance ratios. In particular, we study the behavior of the CO feature at 2.3 $\mu$m with the stellar parameters and we provide empirical fitting functions that can be easily implemented into stellar population models to provide accurate predictions for integrated CO strengths that will help to face outstanding problems in galaxy formation and evolution.