Multi-color photometry in wide field of the Galactic globular cluster NGC 3201 ^*,**

¹ Instituto de Astronomía, Universidad Católica del Norte, Avenida Angamos 0610, Antofagasta, Chile e-mail: vkravtsov@ucn.cl
² Sternberg Astronomical Institute, University Avenue 13, 119899 Moscow, Russia
³ Isaac Newton Institute of Chile, Ministerio de Educación de Chile, Casilla 8-9, Correo 9, Santiago, Chile e-mail: inewton@terra.cl, falvarad@eso.org
⁴ ESO - European Southern Observatory, Alonso de Cordova 3107, Vitacura, Santiago, Chile e-mail: gmarconi@eso.org

Received: 9 July 2008
Accepted: 24 December 2008

Abstract

Aims. This paper aims at further studying one of the nearby Galactic globular clusters (GCs), NGC 3201. It is known to experience notable irregular variability of reddening across its face. By relying on our previous studies and findings and by developing them, we focus on the brighter sequences of the color-magnitude diagram (CMD) and on the cluster's characteristics.

Methods. We carried out and analyzed new multi-color photometry of NGC 3201 in UBVI reaching below the turnoff point in all passbands in a fairly large cluster field, about . To achieve more reliable results and conclusions, we reduced the negative impact of the irregularly varying reddening and contamination by field stars.

Results. With this aim we first estimated mean reddening in different zones of the studied cluster field and then took its variations into account, by reducing them to the same level. We estimated metallicity of NGC 3201 using a new metallicity indicator related to U-based CMDs, recently proposed by us. We find [Fe/H] dex, which falls between extreme estimates of the cluster's metallicity obtained using different methods or indicators. Also, the location of the RGB bump on the branch corresponds to [Fe/H] dex. We isolate 73 probable blue straggler (BS) candidates, the largest population found in NGC 3201 so far. They are more centrally concentrated than the lower red giants at the 99.2% level. Their position in the two-color diagram assumes that presumably none of them belongs to BSa of collisional origin. The luminosity function (LF) of the RGB and its features in the low part of the branch are examined and discussed. We also resolve some of the contradictory results of previous publications.