2010ApJ...708..698D

Query : 2010ApJ...708..698D

2010ApJ...708..698D - Astrophys. J., 708, 698-716 (2010/January-1)

The ACS survey of galactic globular clusters. IX. Horizontal branch morphology and the second parameter phenomenon.

DOTTER A., SARAJEDINI A., ANDERSON J., APARICIO A., BEDIN L.R., CHABOYER B., MAJEWSKI S., MARIN-FRANCH A., MILONE A., PAUST N., PIOTTO G., REID I.N., ROSENBERG A. and SIEGEL M.

Abstract (from CDS):

The horizontal branch (HB) morphology of globular clusters (GCs) is most strongly influenced by metallicity. The second parameter phenomenon, first described in the 1960s, acknowledges that metallicity alone is not enough to describe the HB morphology of all GCs. In particular, astronomers noticed that the outer Galactic halo contains GCs with redder HBs at a given metallicity than are found inside the solar circle. Thus, at least a second parameter was required to characterize HB morphology. While the term "second parameter" has since come to be used in a broader context, its identity with respect to the original problem has not been conclusively determined. Here we analyze the median color difference between the HB and the red giant branch, hereafter denoted as Δ(V - I), measured from Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) photometry of 60 GCs within ∼20 kpc of the Galactic center. Analysis of this homogeneous data set reveals that, after the influence of metallicity has been removed from the data, the correlation between Δ(V - I) and age is stronger than that of any other parameter considered. Expanding the sample to include HST ACS and Wide Field Planetary Camera 2 photometry of the six most distant Galactic GCs lends additional support to the correlation between Δ(V - I) and age. This result is robust with respect to the adopted metallicity scale and the method of age determination, but must bear the caveat that high-quality, detailed abundance information is not available for a significant fraction of the sample. Furthermore, when a subset of GCs with similar metallicities and ages is considered, a correlation between Δ(V - I) and central luminosity density is exposed. With respect to the existence of GCs with anomalously red HBs at a given metallicity, we conclude that age is the second parameter and central density is most likely the third. Important problems related to HB morphology in GCs, notably multi-modal distributions and faint blue tails, remain to be explained.

Abstract Copyright: ∼

Journal keyword(s): globular clusters: general

Simbad objects: 76

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Number of rows : 76
N Identifier Otype ICRS (J2000)
RA 		ICRS (J2000)
DEC 		Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2026 		#notes
1 NGC 104 GlC 00 24 05.359 -72 04 53.20     4.09     ~ 4158 0
2 NGC 288 GlC 00 52 45.24 -26 34 57.4   10 8.13     ~ 1130 0
3 NGC 362 GlC 01 03 14.26 -70 50 55.6     6.58     ~ 1167 0
4 NAME Magellanic Clouds GrG 03 00 -71.0           ~ 7988 0
5 NGC 1261 GlC 03 12 16.21 -55 12 58.4     8.63     ~ 579 0
6 Cl Pal 1 GlC 03 33 20.04 +79 34 51.8   17.2       ~ 267 1
7 NAME E 1 GlC 03 55 02.5 -49 36 52           ~ 229 0
8 NAME Eridanus Star Cluster GlC 04 24 44.5 -21 11 13           ~ 192 1
9 Cl Pal 2 GlC 04 46 05.79720 +31 22 51.0170           ~ 202 0
10 NGC 1851 GlC 05 14 06.76 -40 02 47.6           ~ 1529 0
11 NGC 2298 GlC 06 48 59.41 -36 00 19.1     8.89     ~ 547 0
12 NGC 2419 GlC 07 38 08.51 +38 52 54.9     10.05     ~ 998 0
13 NGC 2808 GlC 09 12 03.10 -64 51 48.6           ~ 1540 0
14 NAME E 3 GlC 09 20 57.07 -77 16 54.8           ~ 185 0
15 NAME Sextans C GlC 10 05 30.96 +00 04 15.4   15.5 13.9     ~ 354 1
16 NGC 3201 GlC 10 17 36.82 -46 24 44.9           ~ 1001 0
17 GCl 17 GlC 11 29 16.80 +28 58 25.0   14.4       ~ 379 1
18 NGC 4147 GlC 12 10 06.149 +18 32 31.78   11.45 10.74     ~ 616 0
19 M 68 GlC 12 39 27.98 -26 44 38.6     7.96     ~ 1069 0
20 NGC 4833 GlC 12 59 33.92 -70 52 35.4           ~ 467 0
21 M 53 GlC 13 12 55.25 +18 10 05.4     7.79     ~ 907 0
22 NGC 5053 GlC 13 16 27.09 +17 42 00.9     9.96     ~ 675 0
23 NGC 5139 GlC 13 26 47.28 -47 28 46.1           ~ 3677 0
24 M 3 GlC 13 42 11.62 +28 22 38.2     6.39     ~ 2593 0
25 NGC 5286 GlC 13 46 26.81 -51 22 27.3           ~ 485 0
26 NGC 5466 GlC 14 05 27.29 +28 32 04.0     9.70     ~ 887 0
27 M 5 GlC 15 18 33.22 +02 04 51.7     5.95     ~ 2095 0
28 NGC 5927 GlC 15 28 00.69 -50 40 22.9           ~ 499 0
29 NGC 5986 GlC 15 46 03.00 -37 47 11.1     6.92     ~ 408 0
30 GCl 38 GlC 16 10 59.00 +14 57 42.0           ~ 399 0
31 Cl Lynga 7 OpC 16 11 03.65 -55 19 04.0           ~ 129 0
32 M 80 GlC 16 17 02.41 -22 58 33.9           ~ 780 0
33 M 4 GlC 16 23 35.22 -26 31 32.7           ~ 1978 0
34 NGC 6101 GlC 16 25 48.12 -72 12 07.9           ~ 337 0
35 NGC 6144 GlC 16 27 13.86 -26 01 24.6           ~ 268 0
36 M 107 GlC 16 32 31.86 -13 03 13.6           ~ 835 0
37 M 13 GlC 16 41 41.634 +36 27 40.75     5.8     ~ 2291 0
38 M 12 GlC 16 47 14.18 -01 56 54.7     6.07     ~ 736 0
39 M 10 GlC 16 57 09.05 -04 06 01.1     4.98     ~ 857 0
40 GCl 50 GlC 16 59 51.1 -00 32 00   15.70       ~ 224 1
41 NGC 6304 GlC 17 14 32.25 -29 27 43.3           ~ 394 0
42 M 92 GlC 17 17 07.39 +43 08 09.4     6.52     ~ 2240 0
43 NGC 6352 GlC 17 25 29.11 -48 25 19.8           ~ 425 0
44 NGC 6366 GlC 17 27 44.24 -05 04 47.5           ~ 344 0
45 NGC 6362 GlC 17 31 54.99 -67 02 54.0           ~ 637 0
46 NGC 6388 GlC 17 36 17.461 -44 44 08.34           ~ 988 1
47 NGC 6397 GlC 17 40 42.09 -53 40 27.6     5.17     ~ 2103 0
48 NAME Galactic Center reg 17 45 39.60213 -29 00 22.0000           ~ 16269 0
49 NGC 6441 GlC 17 50 13.06 -37 03 05.2           ~ 940 0
50 NGC 6496 GlC 17 59 03.68 -44 15 57.4   9.96       ~ 251 0
51 NGC 6535 GlC 18 03 50.51 -00 17 51.5     9.85     ~ 320 0
52 NGC 6541 GlC 18 08 02.36 -43 42 53.6           ~ 409 0
53 NGC 6584 GlC 18 18 37.60 -52 12 56.8     8.17     ~ 317 0
54 NGC 6624 GlC 18 23 40.51 -30 21 39.7           ~ 939 1
55 M 69 GlC 18 31 23.10 -32 20 53.1           ~ 492 0
56 NGC 6652 GlC 18 35 45.63 -32 59 26.6           ~ 474 0
57 M 22 GlC 18 36 23.94 -23 54 17.1           ~ 1459 0
58 M 70 GlC 18 43 12.76 -32 17 31.6           ~ 421 0
59 M 54 GlC 18 55 03.33 -30 28 47.5           ~ 1164 0
60 NGC 6717 GlC 18 55 06.04 -22 42 05.3           ~ 273 0
61 NAME SDG G 18 55 19.0 -30 32 43   4.5 3.6     ~ 2438 2
62 NGC 6723 GlC 18 59 33.15 -36 37 56.1           ~ 543 0
63 NGC 6752 GlC 19 10 52.11 -59 59 04.4           ~ 2121 0
64 M 56 GlC 19 16 35.57 +30 11 00.5           ~ 455 0
65 Cl Terzan 7 GlC 19 17 43.92 -34 39 27.8           ~ 460 0
66 Cl Arp 2 GlC 19 28 44.11 -30 21 20.3     12.41     ~ 384 0
67 M 55 GlC 19 39 59.71 -30 57 53.1     6.49     ~ 913 0
68 Cl Terzan 8 GlC 19 41 44.41 -33 59 58.1     11.54     ~ 357 0
69 M 71 GlC 19 53 46.49 +18 46 45.1           ~ 1190 0
70 NGC 6934 GlC 20 34 11.37 +07 24 16.1           ~ 459 0
71 M 72 GlC 20 53 27.70 -12 32 14.3     8.96     ~ 465 0
72 NGC 7006 GlC 21 01 29.465 +16 11 16.49     10.46     ~ 562 0
73 M 15 GlC 21 29 58.33 +12 10 01.2           ~ 3274 0
74 M 2 GlC 21 33 27.02 -00 49 23.7     6.25     ~ 1114 1
75 M 30 GlC 21 40 22.12 -23 10 47.5     7.10     ~ 1121 0
76 Cl Pal 12 GlC 21 46 38.84 -21 15 09.4     11.89     ~ 548 0

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