Reddening and age for 11 galactic open clusters from integrated spectra

Abstract

We study integrated spectra of 11 Galactic open clusters in the visible and near­ infrared. We use continuum distribution and line strengths to infer reddening, age and, in some cases, metallicity. These parameters are derived by using different methods, mainly by employing template integrated spectra of Magellanic Clouds and Galactic star clusters with known properties, as well as a grid relating the equivalent widths of spectral absorption tines to age and metallicity spanning a wide range of values. The results indicate a good agreement with previous work based mainly on colour-magnitude diagrams, when available. Internal reddening is significant for very young clusters like NGC 3603 and 6611. A Wolf-Rayet star in NGC 6231 is also analysed spectroscopically in the cluster context. Wolf-Rayet features appearing in the integrated spectra of NGC 6231 and 3603 are employed as indicators of the cluster evolutionary stage. The oldest cluster in the sample has an age ~~300 Myr. The present sample considerably improves the age resolution around solar metallicity in the cluster spectrallibrary for population synthesis.