J/A+A/573/A70 UBVI photometry in 3 globular clusters (Nardiello+, 2015)
Observing multiple stellar populations with VLT/FORS2. Main sequence
photometry in outer regions of NGC 6752, NGC 6397, and NGC 6121 (M 4).
Nardiello D., Milone A.P., Piotto G., Marino A.F., Bellini A.,
Cassisi S.
<Astron. Astrophys. 573, A70 (2015)>
=2015A&A...573A..70N 2015A&A...573A..70N (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, globular ; Photometry, UBVRI
Keywords: globular clusters: individual: NGC 6752 - globular cluster: general -
globular clusters: individual: NGC6397 -
globular clusters: individual: NGC6121
Abstract:
We present the photometric analysis of the external regions of three
Galactic Globular Clusters: NGC 6121, NGC 6397 and NGC 6752. The main
goal is the characterization of the multiple stellar populations along
the main sequence (MS) and the study of the radial trend of the
different populations hosted by the target clusters. The data have
been collected using FORS2 mounted at the ESO/VLT@UT1 telescope in
UBVI filters. From these data sets we extracted high-accuracy
photometry and constructed color-magnitude diagrams. We exploit
appropriate combination of colors and magnitudes which are powerful
tools to identify multiple stellar populations, like B versus U-B and
V versus cU,B,I=(U-B)-(B-I) CMDs. We confirm previous findings of a
split MS in NGC 6752 and NGC 6121. Apart from the extreme case of
omega Centauri, this is the first detection of multiple MS from
ground-based photometry. For NGC 6752 and NGC 6121 we compare the
number ratio of the blue MS to the red MS in the cluster outskirts
with the fraction of first and second generation stars measured in the
central regions. There is no evidence for significant radial trend.
The MS of NGC 6397 is consistent with a simple stellar population. We
propose that the lack of multiple sequences is due both to
observational errors and to the limited sensitivity of U,B,V,I
photometry to multiple stellar populations in metal-poor GCs. Finally,
we compute the helium abundance for the stellar populations hosted by
NGC 6121 and NGC 6752, finding a mild (ΔY∼0.02) difference
between stars in the two sequences.
Description:
Astro-photometric catalogs of 3 different FORS2@VLT fields: NGC 6752,
NGC 6397 and NGC 6121 (M 4). For each field we provide equatorial and
FORS2 pixel coordinates, and UBVI photometry.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
ngc6121.dat 131 4055 NGC 6121 astro-photometric catalog
ngc6397.dat 131 8765 NGC 6397 astro-photometric catalog
ngc6752.dat 131 5498 NGC 6752 astro-photometric catalog
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See also:
J/A+A/490/625 : Abundances of NGC 6121 red giants (Marino+, 2008)
J/A+A/425/509 : VI photometry of NGC 6397 (Andreuzzi+, 2004)
J/AJ/120/3111 : Stromgren photometry of NGC 6397 (Anthony-Twarog+, 2000)
J/AJ/135/2141 : NGC 6397 faint stars F814W+F606W photometry (Richer+, 2008)
J/ApJ/709/241 : NGC 6397 X-rays sources Characterisation (Bogdanov+, 2012)
J/ApJ/754/91 : Abundances and velocities of NGC 6397 stars (Lovisi+, 2012)
J/A+A/557/A128 : Stellar [Fe/H] and [Na/H] in NGC6752 (Carretta, 2013)
J/ApJ/750/L14 : Abundances of red giants in NGC 6752 (Carretta+, 2012)
J/MNRAS/423/2901 : NGC 6752 multiwavelength survey (Thomson+, 2012)
Byte-by-byte Description of file: ngc6121.dat ngc6397.dat ngc6752.dat
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Bytes Format Units Label Explanations
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1- 4 I4 --- ID ID number of the star within the cluster
6- 15 F10.6 deg RAdeg Right ascension (J2000)
17- 26 F10.6 deg DEdeg Declination (J2000)
28- 34 F7.2 pix Xpos x master frame position
36- 43 F8.2 pix Ypos y master frame position
45- 50 F6.3 mag Umag Calibrated U Johnson magnitude
52- 56 F5.3 mag e_Umag rms error in the U magnitude
58- 62 F5.3 --- q_Umag Quality of U PSF-fit (1)
64- 65 I2 --- o_Umag [3/23] Number of images for U magnitude
67- 72 F6.3 mag Bmag Calibrated B Johnson magnitude
74- 78 F5.3 mag e_Bmag rms. error in the B magnitude
80- 84 F5.3 --- q_Bmag Quality of B PSF-fit (1)
86- 87 I2 --- o_Bmag [3/33] Number of images for B magnitude
89- 94 F6.3 mag Vmag Calibrated V Johnson magnitude
96-100 F5.3 mag e_Vmag rms. error in the V magnitude
102-106 F5.3 --- q_Vmag Quality of V PSF-fit (1)
108-109 I2 --- o_Vmag [3/46] Number of images for V magnitude
111-116 F6.3 mag Imag Calibrated I Cousins magnitude
118-122 F5.3 mag e_Imag rms. error in the I magnitude
124-128 F5.3 --- q_Imag Quality of I PSF-fit (1)
130-131 I2 --- o_Imag [3/23] Number of images for I magnitude
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Note (1): The quality-fit parameter (QFIT) is a diagnostic related to the
quality of the PSF fit. Small values (QFIT<0.1) are associated to
well measured stars, while larger values (QFIT≥0.5) are
associated to badly measured or non star-like sources.
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Acknowledgements:
Domenico Nardiello, domenico.nardiello(at)studenti.unipd.it
(End) Patricia Vannier [CDS] 31-Oct-2014