A new stellar library in the region of the CO index at 2.3 mu m - New index definition and empirical fitting functions

© ESO 2008. This work was supported by the Spanish research projects AYA2006-14318, AYA2006-15698-C02-02, AYA2007-67752C03-03. E. M. Q. acknowledges the Spanish Ministry of Education and Science and the European Social Found for a Formación de Personal Investigador fellowship under the project AYA2003-01840. A.J.C. is a Juan de la Cierva Fellow of the Spanish Ministry of Education and Science. This research was supported by a Marie Curie Intra-European Fellowship within the 6th European Community Framework Program. Based on observations collected at the Centro Astronomico Hispano Aleman (CAHA) at Calar Alto, operated jointly by the Max-Planck Institut fur Astronomie and the Instituto de Astrofísica de Andalucía (CSIC). Based on observations made with the Italian Telescopio Nazionale Galileo (TNG) operated on the island of La Palma by the Fundación Galileo Galilei of the INAF (Istituto Nazionale di Astrofisica) at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias. This research made use of the SIMBAD database (operated at CDS, Strasbourg, France), the NASA's Astrophysiscs Data System Bibliographic Services, and the Hipparcos Input Catalogue. The authors are grateful to the allocation time committees for the generous concession of observing time. We finally thank the anonymous referee for very useful comments and suggestions.
The analysis of unresolved stellar populations demands evolutionary synthesis models with realistic physical ingredients and extended wavelength coverage. Aims. We quantitatively describe the first CO bandhead at 2.3 mu m to allow stellar population models to provide improved predictions in this wavelength range. Methods. We observed a new stellar library with a better coverage of the stellar atmospheric parameter space than in earlier works. We performed a detailed analysis of the robustness of previous CO index definitions with spectral resolution, wavelength calibration, signal-to-noise ratio, and flux calibration. Results. We define a new line-strength index for the first CO bandhead at 2.3 mu m, DCO, better suited for stellar population studies than previous index definitions. We derive empirical fitting functions for the CO feature as a function of the stellar parameters (T(eff), log g and [Fe/H]), showing a detailed quantitative metallicity dependence.
Spanish research projects
Marie Curie Intra-European Fellowship
Ministerio de Educación y Ciencia
European Social Found for a Formacion de Personal Investigador
Depto. de Física de la Tierra y Astrofísica
Fac. de Ciencias Físicas
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