2010A&A...510A..19L

Current stellar population models have arguably the largest uncertainties in the near-IR wavelength range, partly due to a lack of large and well calibrated empirical spectral libraries. In this paper we present a project whose aim it is to provide the first library of luminosity weighted integrated near-IR spectra of globular clusters to be used to test the current stellar population models and serve as calibrators for future ones. Our pilot study presents spatially integrated K-band spectra of three old (≥10Gyr) and metal poor ([Fe/H]~-1.4), and three intermediate age (1-2Gyr) and more metal rich ([Fe/H]~-0.4) globular clusters in the LMC. We measured the line strengths of the NaI, CaI and ¹²CO(2-0) absorption features. The NaI index decreases with increasing age and decreasing metallicity of the clusters. The D_CO index, used to measure the ¹²CO(2-0) line strength, is significantly reduced by the presence of carbon-rich TP-AGB stars in the globular clusters with age ∼1Gyr. This is in contradiction to the predictions of the stellar population models of Maraston (2005MNRAS.362..799M). We find that this disagreement is due to the different CO absorption strength of carbon-rich Milky Way TP-AGB stars used in the models and the LMC carbon stars in our sample. For globular clusters with age ≥2Gyr we find D_CO index measurements consistent with the model predictions.