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J/A+A/516/A23       UBVI Photometry of NGC 1261             (Kravtsov+, 2010)

Wide-field multi-color photometry of the Galactic globular cluster NGC 1261. Kravtsov V., Alcaino G., Marconi G., Alvarado F. <Astron. Astrophys. 516, A23 (2010)> =2010A&A...516A..23K
ADC_Keywords: Clusters, globular ; Photometry, CCD ; Photometry, UBVRI Keywords: globular clusters: general - globular clusters: individual: NGC 1261 Abstract: 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. 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'x14'. 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 metallicity 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±0.16dex and [Fe/H]ZW=-1.41±0.10dex, 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 Delta V{ZAHB}{clump}=1.01±0.06, that is the difference between the V-levels of the zero age HB and the clump. Description: The observations were made on five nights, 1997 December 27/28, 29/30, 30/31, and 1988 January 01/02, 02/03, with the 1.3 m Warsaw telescope, Las Campanas Observatory, using a set of UBVI filters and a 2048x2048 CCD camera. The array scale is 0.417arcsec/pix, on a field of 14x14'. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file photom.dat 49 5481 Photometric data for 5481 stars in the globular cluster NGC 1261
See also: J/MNRAS/264/273 : CCD photometry of NGC 1261 (Ferraro+ 1993) Byte-by-byte Description of file: photom.dat
Bytes Format Units Label Explanations
1- 4 I4 --- Seq Sequencial number 6- 11 F6.1 pix Xpos X coordinate 13- 18 F6.1 pix Ypos Y coordinate 20- 25 F6.3 mag Vmag V magnitude 27- 32 F6.3 mag U-B ?=- U-B color index (1) 34- 39 F6.3 mag B-V ?=- B-V color index (1) 41- 46 F6.3 mag V-I ?=- V-I color index (1) 48- 49 I2 --- bs ?=- Isolated blue straggler candidates (1)(2)
Note (1): The sign "---" means lack of data Note (2): The number 99 indicates the isolated blue straggler candidates
Acknowledgements: Valery Kravtsov, vkravtsov(at)ucn.cl
(End) V. Kravtsov [Univ. Catolica del Norte], P. Vannier [CDS] 29-Mar-2010
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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