J/A+A/586/A51 JK photometry of NGC 2808 (Massari+, 2016)
GeMS MCAO observations of the Galactic globular cluster NGC 2808:
the absolute age.
Massari D., Fiorentino G., McConnachie A., Bono G., Dall'Ora M.,
Ferraro I., Iannicola G., Stetson P.B., Turri P., Tolstoy E.
<Astron. Astrophys. 586, A51 (2016)>
=2016A&A...586A..51M 2016A&A...586A..51M (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, globular ; Photometry, infrared
Keywords: globular clusters: individual: NGC 2808 -
instrumentation: adaptive optics - techniques: photometric
Abstract:
Globular clusters are the oldest stellar systems in the Milky Way, and
they probe the early epoch of the Galaxy formation. However, the
uncertainties on their absolute age are still too large to soundly
constrain how the Galactic structures have assembled.
The aim of this work is to obtain an accurate estimate of the absolute
age of the globular cluster NGC 2808 using deep IR data obtained with
the multi-conjugate adaptive optics system operating at the Gemini
South telescope (GeMS).
This exquisite photometry, combined with that obtained in V and
I-bands with HST, allowed us to detect the faint Main Sequence Knee
feature in NGC 2808 colour magnitude diagram. The difference between
this point and the main sequence turn-off is a good age estimator that
provides ages with unprecedented accuracy.
Description:
Observing conditions of the nights covered by the GeMS dataset are
described in Table 1. For each of the three nights, the median seeing
as measured by the DIMM is given, together with the adopted filter and
exposure times.
J and K magnitude for the best chip used throughout the analysis are
presented in photom.dat file. Only the magnitude surviving the error
cut shown in Figure 4 are reported in the Table. The position of each
stars is also included (2MASS astrometric system).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 20 7 Observing conditions
photom.dat 46 15306 Photometric data
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Table 2: List of age estimates
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Method Ref Age (Gyr)
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MSK-MSTO 1 10.9±0.7±0.45±0.25
MSTO 1 11.0±2.7±0.10±0.05
MSTO-ZAHB 2 8.4±0.9*
Isochrone fitting 3 12.
Isochrone fitting 4 10.9±0.4*
MSTO-ZAHB + Isochrone fitting 5 11.0±0.4*
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* marks uncertainties on the relative age
References ar follows:
1 = this work
2 = De Angeli et al., 2005AJ....130..116D 2005AJ....130..116D
3 = Piotto et al., 2007ApJ...661L..53P 2007ApJ...661L..53P
4 = Marin-Franch et al., 2009ApJ...694.1498M 2009ApJ...694.1498M
5 = van den Berg et al., 2013ApJ...775..134V 2013ApJ...775..134V
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- Night Night of observation (Month Day)
10 A1 --- Filter [KJ] Filter used
12- 16 A5 --- Texp Exposure time
18- 20 F3.1 arcsec Seeing Seeing
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Byte-by-byte Description of file: photom.dat
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Bytes Format Units Label Explanations
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2- 8 I7 --- ID Star identification number
10- 20 F11.7 deg RAdeg Right ascension (J2000) (1)
22- 32 F11.7 deg DEdeg Declination (J2000) (1)
34- 39 F6.3 mag Jmag J-band magnitude
41- 46 F6.3 mag Kmag K-band magnitude
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Note (1): Positions from 2MASS astrometric system.
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Acknowledgements:
Alexander Kopylov, akop(at)sao.ru
Davide Massari, davidemassari87(at)gmail.com
References:
Kopylova & Kopylov, 1998PAZh...24..573K 1998PAZh...24..573K, (1998AstL...24..491K 1998AstL...24..491K)
Structure and dynamic state of the Corona Borealis supercluster
(End) Davide Massari [INAF-OABO], Patricia Vannier [CDS] 15-Dec-2015