1998A&A...333..505B


Query : 1998A&A...333..505B

1998A&A...333..505B - Astronomy and Astrophysics, volume 333, 505-523 (1998/5-2)

On the relative ages of galactic globular clusters. A new observable, a semi-empirical calibration and problems with the theoretical isochrones.

BUONANNO R., CORSI C.E., PULONE L., FUSI PECCI F. and BELLAZZINI M.

Abstract (from CDS):

A new procedure is described to derive homogeneous relative ages from the Color-Magnitude Diagrams (CMDs) of Galactic globular clusters (GGCs). It is based on the use of a new observable, {DELTA}V0.05 , namely the difference in magnitude between an arbitrary point on the upper main sequence (V+0.05 -the V magnitude of the MS-ridge, 0.05mag redder than the Main Sequence (MS) Turn-off, (TO)) and the horizontal branch (HB). The observational error associated to {DELTA}V0.05 is substantially smaller than that of previous age-indicators, keeping the property of being strictly independent of distance and reddening and of being based on theoretical luminosities rather than on still uncertain theoretical temperatures. As an additional bonus, the theoretical models show that {DELTA}V0.05 has a low dependence on metallicity. Moreover, the estimates of the relative age so obtained are also sufficiently invariant (to within ~±1Gyr) with varying adopted models and transformations. Since the difference in the color difference {DELTA}(B-V)TO,RGB (VandenBerg, Bolte and Stetson 1990 -VBS, Sarajedini and Demarque 1990 -SD) remains the most reliable technique to estimate relative cluster ages for clusters where the horizontal part of the HB is not adequately populated, we have used the differential ages obtained via the "vertical" {DELTA}V0.05 parameter for a selected sample of clusters (with high quality CMDs, well populated HBs, trustworthy calibrations) to perform an empirical calibration of the "horizontal" observable in terms of [Fe/H] and age. A direct comparison with the corresponding calibration derived from the theoretical models reveals the existence of clear-cut discrepancies, which call into question the model scaling with metallicity in the observational planes. Starting from the global sample of considered clusters, we have thus evaluated, within a homogeneous procedure, relative ages for 33 GGCs having different metallicity, HB-morphologies, and galactocentric distances. These new estimates have also been compared with previous latest determinations (Chaboyer, Demarque and Sarajedini (1996ApJ...459..558C), and Richer et al. (1996ApJ...463..602R)). The distribution of the cluster ages with varying metallicity and galactocentric distance are briefly discussed: (a) there is no direct indication for any evident age-metallicity relationship; (b) there is some spread in age (still partially compatible with the errors), and the largest dispersion is found for intermediate metal-poor clusters; (c) older clusters populate both the inner and the outer regions of the Milky Way, while the younger globulars are present only in the outer regions, but the sample is far too poor to yield conclusive evidences.

Abstract Copyright:

Journal keyword(s): stars: evolution - stars: horizontal-branch - stars: Population II - globular clusters: general

Simbad objects: 37

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Number of rows : 37
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2022
#notes
1 NGC 104 GlC 00 24 05.359 -72 04 53.20   5.78 4.09     ~ 3723 0
2 NGC 288 GlC 00 52 45.24 -26 34 57.4   10 8.13     ~ 984 0
3 NGC 362 GlC 01 03 14.26 -70 50 55.6     6.58     ~ 1012 0
4 NGC 1261 GlC 03 12 16.21 -55 12 58.4     8.63     ~ 470 0
5 NGC 1851 GlC 05 14 06.76 -40 02 47.6           ~ 1330 0
6 M 79 GlC 05 24 10.59 -24 31 27.3   9.21 8.16     ~ 762 0
7 NGC 2298 GlC 06 48 59.41 -36 00 19.1   10.77 8.89     ~ 459 0
8 NGC 2808 GlC 09 12 03.10 -64 51 48.6           ~ 1332 0
9 NGC 3201 GlC 10 17 36.82 -46 24 44.9           ~ 797 0
10 NGC 4147 GlC 12 10 06.149 +18 32 31.78   11.45 10.74     ~ 536 0
11 C 1235-509 GlC 12 38 40.20 -51 09 01.0           ~ 345 0
12 M 68 GlC 12 39 27.98 -26 44 38.6   10.26 7.96     ~ 936 0
13 NGC 5053 GlC 13 16 27.09 +17 42 00.9     9.96     ~ 577 0
14 M 3 GlC 13 42 11.62 +28 22 38.2     6.39     ~ 2374 0
15 IC 4499 GlC 15 00 18.57 -82 12 49.6     8.56     ~ 329 0
16 NAME Serpens Dwarf GlC 15 16 05.30 -00 06 41.0   15.1       ~ 682 1
17 M 5 GlC 15 18 33.22 +02 04 51.7   7.34 5.95     ~ 1872 0
18 M 4 GlC 16 23 35.22 -26 31 32.7           ~ 1758 0
19 NGC 6101 GlC 16 25 48.12 -72 12 07.9   10.90 10.08     ~ 265 0
20 M 13 GlC 16 41 41.634 +36 27 40.75     5.8     ~ 2099 0
21 M 12 GlC 16 47 14.18 -01 56 54.7   8.52 6.07     ~ 623 0
22 M 10 GlC 16 57 09.05 -04 06 01.1     4.98     ~ 741 0
23 M 92 GlC 17 17 07.39 +43 08 09.4     6.52     ~ 1997 0
24 NGC 6352 GlC 17 25 29.11 -48 25 19.8   9.95 8.87     ~ 366 0
25 NGC 6362 GlC 17 31 54.99 -67 02 54.0   9.72 8.86     ~ 530 0
26 NGC 6397 GlC 17 40 42.09 -53 40 27.6   7.39 5.17     ~ 1876 1
27 NGC 6553 GlC 18 09 15.68 -25 54 27.9   9.08       ~ 570 0
28 NGC 6584 GlC 18 18 37.60 -52 12 56.8   10.32 8.17     ~ 264 0
29 NGC 6752 GlC 19 10 52.11 -59 59 04.4   6.96 6.28     ~ 1894 0
30 Cl Terzan 7 GlC 19 17 43.92 -34 39 27.8           ~ 396 0
31 Cl Arp 2 GlC 19 28 44.11 -30 21 20.3     12.41     ~ 328 0
32 M 55 GlC 19 39 59.71 -30 57 53.1     6.49     ~ 807 0
33 M 71 GlC 19 53 46.49 +18 46 45.1   7.91 6.1     ~ 1072 0
34 M 15 GlC 21 29 58.33 +12 10 01.2   3       ~ 3021 0
35 M 30 GlC 21 40 22.12 -23 10 47.5     7.10     ~ 978 0
36 Cl Pal 12 GlC 21 46 38.84 -21 15 09.4     11.89     ~ 487 0
37 NGC 7492 GlC 23 08 26.68 -15 36 41.3     10.48     ~ 279 0

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2022.05.29-09:56:43

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