Galactic Clusters Survey

7-year plan

The GCS will image 10 open star clusters and star-formation associations, covering a total area of 1400 sq. degs, in JHK to a depth K=18.7. The survey requires 74 nights of UKIRT time over 7 years.¹ The GCS will be completed in two stages. The first stage is a single pass in JHK over 1400 sq. degs. The second stage is an additional pass in K over the same 1400 sq. degs, for proper motions, with a baseline of at least 2 years. The parameters of the survey are summarised in the table below. The GCS Survey Head is Nige Hambly.

¹ These figures are revised from the original plan (that appears in the Science Case) of 1600 sq. degs requiring 84 nights, because of the revision of the target list following a search for suitable southern clusters.

7-year plan Filter Area
sq. degs
Mag. limit
t(exp.) t(total) Nights
Galactic Clusters Survey
J140019.740s 129h74
H18.840s 129h
K18.740x2s 257h

The GCS will measure the stellar mass function in the sub-stellar régime, down to a mass limit ~25MJupiter, and establish the universality of the IMF, or uncover the important factors that explain variation between clusters. The science goals are described in detail on the science case page (dated Nov. 2001).

The 10 targets are listed in the Table below, and their locations are shown in Fig. 1.

Priority NameTypeRA DecArea
sq. degs
1Pleiadesopen cluster03 47 +24 0779
2Alpha Peropen cluster03 22 +48 3750
3Praesepeopen cluster08 40 +19 4028
4IC 4665open cluster17 46 +05 430.8
5Taurus-AurigaSF assoc.04 30 +25 00386
6OrionSF assoc.05 29 -02 36314.2
7ScoSF assoc.16 10 -23 00154
8Per-OB2SF assoc.03 45 +32 1712.6
9Hyadesopen cluster04 27 +15 52292
10Coma-Beropen cluster12 25 +26 0678.5

Figure 1. Planned final GCS sky coverage. The circles mark the coordinates of the clusters. The size of the symbol scales with the solid angle that will be imaged. The dashed line marks the Galactic plane, and the dotted line marks the ecliptic.

2-year plan

The UKIDSS plan for the first two years of operation is based around an allocation of 290 nights of observing, which is 31% of the 936 nights required to complete the surveys. The GCS will proceed more quickly in the first two years, receiving 30 nights or 41% of the total 74 nights required. The strategy is to cover the entire 1400 sq. degs in a single pass in K, to provide the proper-motion baseline. JH imaging of 460 sq. degs will be completed (one third the total area), essentially following the priority ranking in the table above, modified as follows: only the central 47 sq. degs of the Taurus-Auriga, Orion, and Sco clusters, and the central 146 sq. degs of the Hyades cluster will be imaged, while Coma-Ber will not be imaged. The parameters of the 2-year plan are summarised in the table below.

2-year plan Filter Area
sq. degs
Mag. limit
total nights
Galactic Clusters Survey
J46019.70.33 300.41