Issue |
A&A
Volume 516, June-July 2010
|
|
---|---|---|
Article Number | A23 | |
Number of page(s) | 8 | |
Section | Galactic structure, stellar clusters, and populations | |
DOI | https://doi.org/10.1051/0004-6361/200913449 | |
Published online | 18 June 2010 |
Wide-field multi-color photometry of the Galactic globular cluster NGC 1261*,**
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:
12
October
2009
Accepted:
4
March
2010
Aims. This work studies in more detail the stellar population, including its photometric properties and characteristics, in the rarely studied southern Galactic globular cluster NGC 1261. We focus on the brighter sequences of the cluster's color–magnitude diagram (CMD). Like in our previous works, we rely upon photometry in several passbands to achieve more reliable results and conclusions.
Methods. We carried out and analyzed new multi-color photometry of NGC 1261 in UBVI reaching below the turnoff point in all passbands in a fairly extended cluster field, about 14' × 14'.
Results. We found
several signs of the inhomogeneity (“multiplicity”) in the stellar
population. The most prominent of them are: (1) the
dependence of the radial distribution of sub-giant branch (SGB)
stars in the cluster on their U magnitude, with brighter stars
less centrally concentrated at the 99.9% level than their fainter
counterparts; (2) the dependence of the location of red giant branch
(RGB) stars in the U-(U-B) CMD on their radial distance from the
cluster center, with the portion of stars bluer in the (U-B) color
increasing towards the cluster outskirts. Additionally, the radial
variation of the RGB luminosity function in the bump region is
suspected. We assume that both the SGB stars brighter in the U and
the RGB stars bluer in the (U-B) color are probably associated
with blue horizontal branch stars, because of a
similarity in their radial distribution in the cluster. We estimated
the metalicity of NGC 1261 from the slope of the RGB in U-based CMDs
and the location of the RGB bump on the branch. These metallicity
indicators give [Fe/H]ZW = -1.34 ± 0.16 dex and [Fe/H]ZW
= -1.41 ± 0.10 dex, respectively. We isolated 18 probable blue
straggler candidates. They are more centrally concentrated than the
lower red giants of comparable brightness at the 97.9% level.
Their photometric characteristics imply that their majority
is not consistent with the collisional origin. We also reliably
isolated the asymptotic giant branch (AGB) clump and estimated the
parameter = 1.01 ± 0.06, that is the
difference between the V-levels of the zero age HB and the clump.
Key words: globular clusters: general / globular clusters: individual: NGC 1261
Photometry table is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/516/A23
© ESO, 2010
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