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J/AJ/122/2569 VI photometry of NGC 288, 362 and 1851 (Bellazzini+, 2001)
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Age as the second parameter in NGC 288/NGC 362?
I. Turnoff ages: a purely differential comparison.
Bellazzini M., Pecci F.F., Ferraro F.R., Galleti S., Catelan M.,
Landsman W.B.
<Astron. J. 122, 2569 (2001)>
=2001AJ....122.2569B
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ADC_Keywords: Clusters, globular ; Photometry, CCD
Keywords: color-magnitude diagrams - globular clusters: general -
globular clusters: individual (NGC 288, NGC 362, NGC 1851) -
stars: horizontal-branch - stars: Population II
Abstract:
We present deep V, I photometry of the globular clusters NGC 288, 362,
and 1851 obtained during a single observational run under strictly
homogeneous conditions. We use the bimodal horizontal branch (HB) of
NGC 1851 as a "bridge" to obtain the optimum relative match between
the HBs of NGC 288 and NGC 362. In this way we can effectively remove
the uncertainties associated with distance, reddening, and
inhomogeneities in the absolute calibration, thus obtaining a very
robust, purely differential estimate of the age difference between
these two clusters. According to the bridge test, NGC 288 is found to
be older than NGC 362 by 2+/-1Gyr.
The observations were carried out during the nights of 1997 January 2
and 3 at the 2.2 m ESO/MPI telescope at La Silla (Chile), with the
EFOSC2 camera equipped with a Loral/Lesser 2048x2048 pixel CCD. The
pixel scale is 0.26"/pix, and the effective field of view is
8x8arcmin^2^. The gain is 1.63 e^-^ADU^-^, and the readout noise is
6.3 e^-^rms. The seeing conditions were average during the January 2
night (~1.3") when the NGC 1851 and NGC 288 observations were carried
out, and they worsened (~2") during the second night when we observed
NGC 362.
Objects:
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RA (2000) DE Designation(s)
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00 52 45.3 -26 34 43 NGC 288
01 03 14.3 -70 50 54 NGC 362
05 14 06.3 -40 02 50 NGC 1851
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 65 10990 Photometry of NGC 288
table2.dat 63 9118 Photometry of NGC 1851
table3.dat 63 7492 Photometry of NGC 362
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Byte-by-byte Description of file: table1.dat, table2.dat, table3.dat
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Bytes Format Units Label Explanations
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1- 5 I5 --- BPF Object identification (1)
8- 13 F6.3 mag Vmag The V band magnitude
16- 20 F5.3 mag e_Vmag Error in Vmag
23- 28 F6.3 mag Imag The I band magnitude
31- 35 F5.3 mag e_Imag Error in Imag
39- 45 F7.2 pix Xpix The X pixel position (2)
48- 55 F8.2 pix Ypix The Y pixel position (2)
58- 65 A8 --- Name Other object identification (3)
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Note (1): In Simbad, the designations are:
Cl* NGC 288 BPF NNNNN in table1.dat
Cl* NGC 1851 BPF NNNN in table2.dat
Cl* NGC 362 BPF NNNN in table3.dat
Note (2): 1 pix = 0.26"
Note (3): Other object identification:
V# = Cl* NGC AAAA SAW VNN in Simbad e.g.
Cl* NGC 288 Saw VN, RR Lyrae variables found by Kaluzny
(1996A&AS..120...83K) in table1.dat,
Cl* NGC 1851 SAW VNN, RR Lyrae variables in common with Walker
(1998AJ....116..220W) in table2.dat
Cl* NGC 362 SAW VNNN, RR Lyrae variables identified in the
Sawyer-Hogg (1973, updated by C. Clement, 1997, Cat. <V/97>),
in table3.dat
Guo 4110 = A non member star identified in the proper motions database
by Guo (1995, Ph.D. thesis, Yale Univ.);
EHB1 = The extreme HB star identified by Bellazzini & Messineo (1999,
in The Chemical Evolution of the Milky Way: Stars versus
Clusters, ed. F. Matteucci & F. Giovannelli (Dordrecht:
Kluwer), 213).
UIT-# = UV sources identified by the UIT satellite (see Cat. <VI/104>)
PNM = probable non member (only for stars near the HB) according to
Tucholke (1992, Cat. <J/A+AS/93/311>).
MJ #### = Cl* NGC 362 MJ NNNNN, BHB star that is a confirmed member of the
cluster according to Moehler et al. (2000A&A...361..937M).
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History:
From electronic version of the journal
Comments: Modifications made from the original:
in "Other object identification" column
for Cl* NGC 1851 BPF 617, No 8 identified to Cl* NGC 1851 SAW V8
for Cl* NGC 362 BPF 1898, No 3 identified to Cl* NGC 362 SAW V3
for Cl* NGC 362 BPF 134, No 5 identified to Cl* NGC 362 SAW V5
References:
Catelan, 2000ApJ...531..826C
Catelan et al., 2001ApJ...560..970C
Catelan et al., paper II 2001AJ....122.3171C
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(End) Greg Schwarz [AAS], Patricia Bauer [CDS] 18-Jan-2002