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

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 14 × 14 . 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] ZW = −1.54 ± 0.12 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] ZW = −1.46 ± 0.15 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.

The radial distribution of stars of different stellar generations in the globular cluster NGC 3201

“…However, the novelty presented in this Note is that we can exploit this property to get independent insight into the radial distributions of stars in NGC 3201, which is completely free of any bias in the spectroscopic sample. Kravtsov et al (2010) find signs of multiple sequences among subgiant branch stars in this GC, with stars at different magnitude levels primarily lying at different radial distances, (Kravtsov et al 2009) for RGB stars of NGC 3201 in common with Carretta et al (2009a,b). Blue circles and red filled triangles corresponds to the two different intervals in radial distances used in Kravtsov et al (2010).…”

“…Much more significant are the differences in colour observed along the RGB for the P, I, and E populations, in particular when using the U − B colour. We do not have U in our photometric database, so we cross-identified our stars with the multi-colour photometry of more than 12 000 stars in NGC 3201 by Kravtsov et al (2009). We used software written by P. Montegriffo at the Bologna Observatory and found 138 stars (out of 150) in common between the two samples.…”

“…As a result, the radial distributions of first and second-generation stars can no longer be distinguished from their dynamics alone at the present time. In this Note we combine information from our ongoing FLAMES survey of chemical abundances in giants in GCs (see with newly derived photometry for the GC NGC 3201 ( Kravtsov et al 2009Kravtsov et al , 2010, and we provide new insight into the radial distribution of first and second-generation stars in this GC, whose relaxation time at half-mass radius is about 1.6 Gyr (Harris 1996).…”

Evidence of the inhomogeneity of the stellar population in the differentially reddened globular cluster NGC 3201

“…For our analysis of the RGB of NGC 3201, we used a ready-made sample of the most probable RGB stars. Their selection was done previously and is described in detail in Kravtsov et al (2009). Based on this sample we found as in the RGB of NGC 1261 a systematically different location in the U − (U − B) diagram of RGB stars situated at different radial distances from the cluster center, where the portion of stars bluer in the (U − B) systematically increased towards the cluster outskirts.…”

“…For a description of the photometric data used here (and publicly available in electronic form) and of the typical rms errors in each passband, see Kravtsov et al (2009). In the same paper, we also described in detail our study of the variation of reddening in the observed cluster field and listed the estimated corrections corresponding to areas with conditionally defined grades of reddening.…”