2013ApJ...775..134V


Query : 2013ApJ...775..134V

2013ApJ...775..134V - Astrophys. J., 775, 134 (2013/October-1)

The ages of 55 globular clusters as determined using an improved ΔVTOHB method along with color-magnitude diagram constraints, and their implications for broader issues.

VANDENBERG D.A., BROGAARD K., LEAMAN R. and CASAGRANDE L.

Abstract (from CDS):

Ages have been derived for 55 globular clusters (GCs) for which Hubble Space Telescope Advanced Camera for Surveys photometry is publicly available. For most of them, the assumed distances are based on fits of theoretical zero-age horizontal-branch (ZAHB) loci to the lower bound of the observed distributions of HB stars, assuming reddenings from empirical dust maps and metallicities from the latest spectroscopic analyses. The age of the isochrone that provides the best fit to the stars in the vicinity of the turnoff (TO) is taken to be the best estimate of the cluster age. The morphology of isochrones between the TO and the beginning part of the subgiant branch (SGB) is shown to be nearly independent of age and chemical abundances. For well-defined color-magnitude diagrams (CMDs), the error bar arising just from the "fitting" of ZAHBs and isochrones is ~±0.25 Gyr, while that associated with distance and chemical abundance uncertainties is ~±1.5-2 Gyr. The oldest GCs in our sample are predicted to have ages of ~13.0 Gyr (subject to the aforementioned uncertainties). However, the main focus of this investigation is on relative GC ages. In conflict with recent findings based on the relative main-sequence fitting method, which have been studied in some detail and reconciled with our results, ages are found to vary from mean values of ~12.5 Gyr at [Fe/H] ≲ - 1.7 to ~11 Gyr at [Fe/H] ≳ -1. At intermediate metallicities, the age-metallicity relation (AMR) appears to be bifurcated: one branch apparently contains clusters with disk-like kinematics, whereas the other branch, which is displaced to lower [Fe/H] values by ~0.6 dex at a fixed age, is populated by clusters with halo-type orbits. The dispersion in age about each component of the AMR is ~±0.5 Gyr. There is no apparent dependence of age on Galactocentric distance (RG) nor is there a clear correlation of HB type with age. As previously discovered in the case of M3 and M13, subtle variations have been found in the slope of the SGB in the CMDs of other metal-poor ([Fe/H] ≲ - 1.5) GCs. They have been tentatively attributed to cluster-to-cluster differences in the abundance of helium. Curiously, GCs that have relatively steep "M13-like" SGBs tend to be massive systems, located at small RG, that show the strongest evidence of in situ formation of multiple stellar populations. The clusters in the other group are typically low-mass systems (with 2-3 exceptions, including M3) that, at the present time, should not be able to retain the matter lost by mass-losing stars due either to the development of GC winds or to ram-pressure stripping by the halo interstellar medium. The apparent separation of the two groups in terms of their present-day gas retention properties is difficult to understand if all GCs were initially ∼20 times their current masses. The lowest-mass systems, in particular, may have never been massive enough to retain enough gas to produce a significant population of second-generation stars. In this case, the observed light element abundance variations, which are characteristic of all GCs, were presumably present in the gas out of which the observed cluster stars formed.

Abstract Copyright:

Journal keyword(s): globular clusters: general - stars: abundances - stars: evolution - stars: interiors - stars: Population II

Simbad objects: 72

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Number of rows : 72
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     ~ 3752 0
2 NGC 288 GlC 00 52 45.24 -26 34 57.4   10 8.13     ~ 993 0
3 NGC 362 GlC 01 03 14.26 -70 50 55.6     6.58     ~ 1020 0
4 NGC 1261 GlC 03 12 16.21 -55 12 58.4     8.63     ~ 477 0
5 Cl Pal 1 GlC 03 33 20.04 +79 34 51.8   17.2       ~ 225 1
6 NGC 1851 GlC 05 14 06.76 -40 02 47.6           ~ 1343 0
7 NAME LMC G 05 23 34.6 -69 45 22     0.4     ~ 16284 1
8 NGC 2298 GlC 06 48 59.41 -36 00 19.1     8.89     ~ 465 0
9 NGC 2808 GlC 09 12 03.10 -64 51 48.6           ~ 1346 0
10 NAME E 3 GlC 09 20 57.07 -77 16 54.8           ~ 151 0
11 NGC 3201 GlC 10 17 36.82 -46 24 44.9           ~ 804 0
12 NGC 4147 GlC 12 10 06.149 +18 32 31.78   11.45 10.74     ~ 542 0
13 M 68 GlC 12 39 27.98 -26 44 38.6   10.26 7.96     ~ 942 0
14 NGC 4833 GlC 12 59 33.92 -70 52 35.4   8.72 7.79     ~ 390 0
15 M 53 GlC 13 12 55.25 +18 10 05.4   8.95 7.79     ~ 780 0
16 NGC 5053 GlC 13 16 27.09 +17 42 00.9     9.96     ~ 584 0
17 NGC 5139 GlC 13 26 47.28 -47 28 46.1   6.12 5.33     ~ 3266 0
18 M 3 GlC 13 42 11.62 +28 22 38.2     6.39     ~ 2385 0
19 NGC 5286 GlC 13 46 26.81 -51 22 27.3   9.18 8.31     ~ 408 0
20 NGC 5466 GlC 14 05 27.29 +28 32 04.0   10.5 9.70     ~ 786 0
21 M 5 GlC 15 18 33.22 +02 04 51.7   7.34 5.95     ~ 1889 0
22 NGC 5927 GlC 15 28 00.69 -50 40 22.9   10.13 8.86     ~ 435 0
23 HD 140283 Pe* 15 43 03.0971190219 -10 56 00.595693188 7.508 7.711 7.212 6.63 8.21 F9VkA5mA1 897 0
24 NGC 5986 GlC 15 46 03.00 -37 47 11.1     6.92     ~ 341 0
25 Cl Lynga 7 GlC 16 11 03.65 -55 19 04.0           ~ 103 0
26 M 80 GlC 16 17 02.41 -22 58 33.9           ~ 673 0
27 M 4 GlC 16 23 35.22 -26 31 32.7           ~ 1772 0
28 NGC 6101 GlC 16 25 48.12 -72 12 07.9   10.90 10.08     ~ 268 0
29 NGC 6144 GlC 16 27 13.86 -26 01 24.6   10.55 9.63     ~ 226 0
30 V* UV Oct RR* 16 32 25.5361202856 -83 54 10.495880892   9.80 9.44     A8/F0Ia/ab(w) 113 0
31 M 107 GlC 16 32 31.86 -13 03 13.6   9.96 8.85     ~ 753 0
32 M 13 GlC 16 41 41.634 +36 27 40.75     5.8     ~ 2117 0
33 M 12 GlC 16 47 14.18 -01 56 54.7   8.52 6.07     ~ 629 0
34 M 10 GlC 16 57 09.05 -04 06 01.1     4.98     ~ 749 0
35 NGC 6304 GlC 17 14 32.25 -29 27 43.3   10.33 9.03     ~ 332 0
36 M 92 GlC 17 17 07.39 +43 08 09.4     6.52     ~ 2009 0
37 NGC 6352 GlC 17 25 29.11 -48 25 19.8   9.95 8.87     ~ 373 0
38 NGC 6366 GlC 17 27 44.24 -05 04 47.5           ~ 287 0
39 NGC 6362 GlC 17 31 54.99 -67 02 54.0   9.72 8.86     ~ 542 0
40 NGC 6388 GlC 17 36 17.461 -44 44 08.34   7.40       ~ 868 1
41 NGC 6397 GlC 17 40 42.09 -53 40 27.6     5.17     ~ 1894 1
42 NAME Galactic Center reg 17 45 39.60213 -29 00 22.0000           ~ 13204 0
43 NGC 6441 GlC 17 50 13.06 -37 03 05.2   9.26 8.00     ~ 836 0
44 NGC 6496 GlC 17 59 03.68 -44 15 57.4   9.96       ~ 208 0
45 NGC 6535 GlC 18 03 50.51 -00 17 51.5   11.35 9.85     ~ 272 0
46 NGC 6541 GlC 18 08 02.36 -43 42 53.6   8.06 7.32     ~ 350 1
47 NGC 6584 GlC 18 18 37.60 -52 12 56.8   10.32 8.17     ~ 269 0
48 NGC 6624 GlC 18 23 40.51 -30 21 39.7           ~ 834 1
49 M 69 GlC 18 31 23.10 -32 20 53.1   9.32 8.31     ~ 441 1
50 NGC 6652 GlC 18 35 45.63 -32 59 26.6   10.64 9.75     ~ 397 0
51 M 22 GlC 18 36 23.94 -23 54 17.1   7.16 6.17     ~ 1306 0
52 M 70 GlC 18 43 12.76 -32 17 31.6   9.76 9.06     ~ 358 0
53 NAME SDG G 18 55 03.1 -30 28 42   4.5 3.6     ~ 1994 2
54 M 54 GlC 18 55 03.33 -30 28 47.5           ~ 1009 0
55 NGC 6717 GlC 18 55 06.04 -22 42 05.3   11.29 10.35     ~ 224 0
56 NGC 6723 GlC 18 59 33.15 -36 37 56.1           ~ 473 0
57 NGC 6752 GlC 19 10 52.11 -59 59 04.4   6.96 6.28     ~ 1911 0
58 M 56 GlC 19 16 35.57 +30 11 00.5   8.90       ~ 397 0
59 Cl Terzan 7 GlC 19 17 43.92 -34 39 27.8           ~ 403 0
60 NGC 6791 OpC 19 20 53 +37 46.7   10.52 9.5     ~ 973 0
61 Cl Arp 2 GlC 19 28 44.11 -30 21 20.3     12.41     ~ 335 0
62 M 55 GlC 19 39 59.71 -30 57 53.1     6.49     ~ 813 0
63 Cl Terzan 8 GlC 19 41 44.41 -33 59 58.1     11.54     ~ 297 0
64 M 71 GlC 19 53 46.49 +18 46 45.1   7.91 6.1     ~ 1079 0
65 NGC 6934 GlC 20 34 11.37 +07 24 16.1   10.48 9.75     ~ 393 0
66 M 72 GlC 20 53 27.70 -12 32 14.3   9.95 8.96     ~ 397 0
67 M 15 GlC 21 29 58.33 +12 10 01.2   3       ~ 3039 0
68 M 2 GlC 21 33 27.02 -00 49 23.7     6.25     ~ 972 1
69 M 30 GlC 21 40 22.12 -23 10 47.5     7.10     ~ 988 0
70 Cl Pal 12 GlC 21 46 38.84 -21 15 09.4     11.89     ~ 493 0
71 NGC 7492 GlC 23 08 26.68 -15 36 41.3     10.48     ~ 283 0
72 NAME Galactic Bulge reg ~ ~           ~ 3938 0

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2022.10.07-04:15:55

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