A new stellar library in the region of the CO index at 2.3 m - New index definition and empirical fitting functionsE. Mármol-Queraltó, N. Cardiel, A. J. Cenarro, A. Vazdekis, J. Gorgas, S. Pedraz, R. F. Peletier and P. Sánchez-BlázquezA&A, 489 2 (2008) 885-909DOI: https://doi.org/10.1051/0004-6361:200810044