The ACS Globular Cluster Survey



The Target List

The program includes 66 Galactic globular clusters, which were selected with respect to distance ( (m-M)V <≈16.5), and differential reddening (E(B-V) <≈ 0.35). From the latest version of the Harris (1996) catalog 55 GCs are included in the target list (Table 1). In addition we include NGC 5927, NGC 6304, NGC 6366 as metal-rich thick disk/ bulge clusters. NGC 6441 and NGC 6388, also metal-rich, with a predominantly red horizontal branch (HB) but also featuring an anomalous blue component to their HBs (Rich et al. 1997) are also part of this program. To determine the age of those globular clusters special care has to be taken in eliminating field stars from their CMDs. Similarly, NGC 6715 (M54), Terzan 7, Terzan 8, and Arp 2 are included. Although 0.5 to 1 mag further than our nominal distance limit, these clusters are of special interest due to their connection to the Sagittarius dwarf galaxy and its formation and dynamical history (Layden & Sarajedini 2000, Majewski et al. 2003).

Table 1: Target list for the GC Treasury program

Target

RA(2000)

DEC(2000)

Magnitude

NGC 104 (47Tuc)

00 24 5.20

-72 04 51.00

V=3.95

NGC 288

00 52 47.50

-26 35 24.00

V=8.09

NGC 362

01 03 14.30

-70 50 54.00

V=6.4

NGC 1261

03 12 15.30

-55 13 1.00

V=8.29

Palomar1

03 33 23.00

+79 34 50.00

V=13.18

NGC 1851

05 14 6.30

-40 02 50.00

V=7.14

NGC 1904

05 24 10.60

-24 31 27.00

V=7.73

NGC 2298

06 48 59.20

-36 00 19.00

V=9.29

NGC 2808

09 12 2.60

-64 51 47.00

V=6.2

E3

09 20 59.30

-77 16 57.00

V=11.35

NGC 3201

10 17 36.80

-46 24 40.00

V=6.75

NGC 4147

12 10 6.20

+18 32 31.00

V=10.32

NGC 4590

12 39 28.00

-26 44 34.00

V=7.84

NGC 4833

12 59 35.00

-70 52 29.00

V=6.91

NGC 5024

13 12 55.30

+18 10 9.00

V=7.61

NGC 5053

13 16 45.00

+17 41 53.00

V=9.47

NGC 5139

13 26 45.90

-47 28 37.00

V=3.68

NGC 5272

13 42 11.20

+28 22 32.00

V=6.19

NGC 5286

13 46 26.50

-51 22 24.00

V=7.34

NGC 5466

14 05 27.30

+28 32 4.00

V=9.04

NGC 5897

15 17 24.50

-21 00 37.00

V=8.53

NGC 5904

15 18 33.80

+02 04 58.00

V=5.65

NGC 5927

15 28 0.50

-50 40 22.00

V=8.01

NGC 5986

15 46 3.50

-37 47 10.00

V=7.52

NGC 6093

16 17 2.50

-22 58 30.00

V=7.33

NGC 6101

16 25 48.60

-72 12 6.00

V=9.16

NGC 6121

16 23 35.50

-26 31 31.00

V=5.63

NGC 6171

16 32 31.90

-13 03 13.00

V=7.93

NGC 6205

16 41 41.50

+36 27 37.00

V=5.78

NGC 6218

16 47 14.50

-01 56 52.00

V=6.7

NGC 6254

16 57 8.90

-04 05 58.00

V=6.6

NGC 6304

17 14 32.10

-29 27 44.00

V=8.22

NGC 6341

17 17 7.30

+43 08 11.00

V=6.44

NGC 6352

17 25 29.20

-48 25 22.00

V=7.96

NGC 6362

17 31 54.80

-67 02 53.00

V=7.73

NGC 6366

17 27 44.30

-05 04 36.00

V=9.2

NGC 6388

17 36 17.00

-44 44 6.00

V=6.72

NGC 6397

17 40 41.30

-53 40 25.00

V=5.73

NGC 6441

17 50 12.90

-37 03 5.00

V=7.15

NGC 6496

17 59 2.00

-44 15 54.00

V=8.54

NGC 6535

18 03 50.70

-00 17 49.00

V=10.47

NGC 6541

18 08 2.20

-43 30 0.00

V=6.3

NGC 6584

18 18 37.70

-52 12 54.00

V=8.27

NGC 6624

18 23 40.50

-30 21 40.00

V=7.87

NGC 6637

18 31 23.10

-32 20 53.00

V=7.64

NGC 6652

18 35 45.70

-32 59 25.00

V=8.62

NGC 6656

18 36 24.20

-23 54 12.00

V=5.1

NGC 6681

18 43 12.70

-32 17 31.00

V=7.87

NGC 6715

18 55 3.30

-30 28 42.00

V=7.6

NGC 6717

18 55 6.20

-22 42 3.00

V=9.28

NGC 6723

18 59 33.20

-36 37 54.00

V=7.01

NGC 6752

19 10 53.00

-59 59 5.00

V=5.4

NGC 6779

19 16 35.50

+30 11 5.00

V=8.27

Terzan7

19 17 43.70

-34 39 27.00

V=12.0

Arp2

19 28 44.10

-30 21 14.00

V=12.3

NGC 6809

19 39 59.40

-30 57 44.00

V=6.32

Terzan8

19 41 45.00

-34 00 1.00

V=12.4

NGC 6838

19 53 46.10

+18 46 42.00

V=8.19

NGC 6934

20 34 11.60

+07 24 15.00

V=8.83

NGC 6981

20 53 27.90

-12 32 13.00

V=9.27

NGC 7078

21 29 58.30

+12 10 1.00

V=6.2

NGC 7089

21 33 29.30

-00 49 23.00

V=6.47

NGC 7099

21 40 22.00

-23 10 45.00

V=7.19

Palomar12

21 46 38.80

-21 15 3.00

V=11.99

Palomar2

04 46 5.90

+31 22 51.00

V=13.04

Lynga7

16 11 3.00

-55 18 52.00

V=14.0



Among the Sgr GCs the hypothetical nucleus of this dwarf galaxy, NGC 6715, is of special interest. Additional observing time was assigned to this cluster, to ensure that we can adequately study the mass function of its lower main sequence. To probe the properties of the Sgr dwarf in even more detail the Palomar 2 cluster is included as well, which Majewski et al. (2004) find to be associated with Sgr. The Lynga 7 cluster is a 'transition cluster' (Frinchaboy et al. 2004) with properties between the Galactic globular clusters and the open clusters and is included in our target list as well. We note, that clusters such as NGC 4372, NGC 5986, NGC 6144, NGC 6266, NGC 6544, and NGC 6638 are not included because they are known to have significant and difficult-to-model differential reddening. Ground based surveys on metal-rich clusters are somewhat hampered by differential reddening as well as by the contamination with field stars. Therefore we deliberately include a significant number of those clusters in our program. With the ACS instrument it will be possible to build sub-samples of stars in individual ares of a given cluster and to address the problem of differential reddening. Precise photometry from ACS in the cluster core will help to minimize the effects of field contamination.