2 Observations and reductions

UKS 2 was observed at ESO (La Silla) with the 1.54 m Danish telescope in the night of 1988, March 18-19.

The 1024 $\times$ 620 RCA CCD ESO # 8 was employed, which has pixel size of 15 $\mu$m (0.235'' on the sky), and the frame size is 4 $' \times 2.4'$. We show in Fig. 1 a V image of UKS 2. The bright star in the image is in the Tycho catalogue, while no Hipparcos's star is present. The J2000 coordinates given in Sect. 1 were measured by ourselves on a digitized Sky Survey extraction, taking into account the highest concentration of stars seen in the CCD frame.

The log of observations is given in Table 1.

Figure 1: 4 min V image of UKS 2. Dimensions are $4' \times 2.4'$. North is up and west to the left. Open squares mark red giants from left to right: 5, 1, 4, 3, 2

The transformation equations are

$V\; =\; 23.82\;+\;v$ $B\; =\; b\;+\;24.44\;+\; 0.09(B-V)$

where coefficients are for 5 s (V) and 15 s (B) exposures and airmass of 1.15. The stellar photometry was made with the DAOPHOT II code in MIDAS environment. For the calibrations 29 independent B and V frames of 5 different Landolt (1983) standard stars were used. More specifications on this run can be found in the study of NGC 6553 (Ortolani et al. 1990).

The frame to frame photometric errors computed from the long and short exposures are $\Delta V = 0.01$ mag for 16 < V < 17, 0.05 mag for 17 < V < 20, and 0.09 for 20 < V < 21. The B-V errors are about 10% higher. It is well known that the true errors are somewhat larger than the frame to frame spread, because the two frames are affected by the same crowding and flatfield residuals.

In Tables 2 and 3, available only in electronic form at the CDS-Strasbourg, are given respectively, the stars within r < 200 pixels centered on the cluster (210 stars), and all 735 stars present in the full field.

   

Table 1: Log of observations

Target	Filter	Date	Exp.	Seeing
			${\rm (min)}$	('')
UKS 2	B	18.3.88	30	0.85
	V	''	40	''
	B	''	25	''
	B	''	7	''
	V	''	4	''