2 Observations and data reduction

Observations were carried out with the AFOSC camera at the 1.82 m Copernico telescope of Cima Ekar (Asiago, Italy), on the photometric night of October 21, 2001. AFOSC samples a $8^\prime.14\times8^\prime.14$ field in a 1K $\times$ 1K thinned CCD. The typical seeing was between 2.0 and 2.5 arcsec. The basic data of the studied clusters are summarized in Table 1, and the details of the observations are listed in Table 2. The covered regions are shown in Figs. 1 and 6, where two DSS maps are presented for NGC 7036 and NGC 7772, respectively. The data have been reduced using the IRAF packages CCDRED, DAOPHOT, and PHOTCAL. The calibration equations obtained by observing the Landolt (1992) PG 02331 field 3 times during the night, are:

 

$$U + 3.707\pm0.054 + (0.201\pm0.060)(U\!-\!B) + 0.58\,X$$                u =

$$B + 1.545\pm0.006 - (0.068\pm0.007)(B\!-\!V) + 0.29\,X$$ b =

$$V + 0.893\pm0.029 + (0.010\pm0.011)(B\!-\!V) + 0.16\,X$$ v =

$$I + 1.624\pm0.017 - (0.051\pm0.015)(V\!-\!I) + 0.08\,X$$ i = (1)

where UBVI are standard magnitudes, ubvi are the instrumental ones, and X is the airmass. The standard stars in this field provide a very good color coverage, being $-0.329 \leq (B-V) \leq 1.448$. For the extinction coefficients, we assumed the typical values for the Asiago Observatory (Desidera et al. 2001). Photometric global errors have been estimated following Patat & Carraro (2001). For the V filter, they amount to 0.03, 0.05 and 0.07 at $V\approx$12.0, 16.0 and 20.0, respectively.

 

Table 2: Journal of observations of NGC 7036 and NGC 7772 and standard star field PG 02331 (October 21, 2001).

Field	Filter	Time integration	Seeing
		(s)	( $\prime\prime$)
NGC 7036
	U	240, 600	2.2
	B	30, 300	2.3
	V	30, 300	2.3
	I	30, 200	2.3
NGC 7772
	U	300	2.2
	B	30, 120	2.4
	V	5, 15, 60	2.3
	I	5, 15, 60	2.3
PG 02331
	U	60, 120, 60	2.0
	B	60, 60, 120	2.1
	V	15, 15, 30, 30	2.0
	I	30, 30, 15	2.1

Figure 1: A DSS red map of the covered region in the field of NGC 7036. North is up, East on the left.