IR photometric properties of Red Giants in ω Cen^*,**

¹ Dipartimento di Astronomia, Università di Bologna, via Ranzani 1, 40127 Bologna, Italy e-mail: ferraro@bo.astro.it; s_sollima@astbo4.bo.astro.it
² Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy

Corresponding author: A. Sollima, s_sollima@astbo4.bo.astro.it

Received: 5 November 2003
Accepted: 27 January 2004

Abstract

We present a near-infrared J and K photometric catalog containing more than 73 000 stars in the central region of the giant Globular Cluster ω Centauri. This is the largest IR data set ever published for this cluster and has been used to completely characterize the morphology and the properties of the Red Giant Branch (RGB). In particular, we concentrated our attention on (i) the anomalous RGB (RGB-a), recently discovered in this cluster and (ii) the RGB of the dominant metal poor population (RGB-MP) in both the infrared and optical-infrared color magnitude diagrams. The full set of morphological parameters and photometric indices has been measured and compared with the empirical relations by Ferraro et al. ([CITE]). We find that the detailed photometric properties of the RGB-a are in full agreement with the recent spectroscopic metallicity estimates that place it at the metal-rich extreme of the stellar population mix in ω Centauri.