2 Observations and data reduction

 

Table 1: Basic parameters of the observed objects. Coordinates are for J2000.0 equinox.

Name	$\alpha$	$\delta$	l	b
	hh:mm:ss	$^{\rm o}$ : $^{\prime}$ :  $^{\prime\prime}$	$^{\rm o}$	$^{\rm o}$
NGC 133	00:31:12	+63:22:00	120.67	+0.58
NGC 1348	03:34:10	+51:24:46	146.97	-3.70

Observations were carried out with the AFOSC camera at the 1.82 m Copernico telescope of Cima Ekar (Asiago, Italy), in the photometric night of December 18, 2001. AFOSC samples a $8\farcs14\times8\farcs 14$ field in a $1~{\rm K}\times 1~{\rm K}$ thinned CCD. The typical seeing was around 2.0 arcsec.

The basic data of the studied objects are summarized in Table 1, whereas the details of the observations are listed in Table 2, where the observed fields are reported together with the exposure times, the typical seeing and the airmass. The covered regions are shown in Figs. 1 and 8, where two XDSS maps are presented for NGC 133 and NGC 1348, respectively. The data has been reduced by using the IRAF packages CCDRED, DAOPHOT, and PHOTCAL. The calibration equations obtained by observing Landolt (1992) SA 93, PG 1047+003, PG 2331+055 and PG 0231+051 fields along the night, are:

$$u = U + 3.520\pm0.042 + (0.099\pm0.030)(U\!-\!B)\! + 0.58~X$$

$$b = B + 1.407\pm0.012 - (0.004\pm0.017)(B\!-\!V)\! + 0.29~X \\$$

$$v = V + 0.752\pm0.009 + (0.036\pm0.012)(B\!-\!V)\! + 0.16~X \\$$

 

$$i = I + 1.619\pm0.017 - (0.011\pm0.015)(V\!-\!I)\! + 0.08~X$$ (1)

where UBVI are standard magnitudes, ubvi are the instrumental ones, and X is the airmass. The standard stars in these fields provide a very good color coverage. 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 at 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 133, NGC 1348, and standard star fields (December 18, 2001).

Field	Filter	Time integration	Seeing	Airmass
		(s)	( $\prime\prime$)
SA 93
	U	120	1.9	1.307
	B	60, 60	2.0	1.314
	V	30, 30, 30	2.0	1.316
	I	30, 30	2.0	1.319
NGC 133
	U	60	2.2	1.065
	B	5, 10, 30	2.1	1.068
	V	3, 10, 30	2.3	1.061
	I	3, 10	2.3	1.067
PG 1047+003
	U	120	1.9	1.245
	B	60, 60	2.0	1.240
	V	30, 30	2.0	1.250
	I	30, 30	2.0	1.238
PG 0231+051
	U	120	1.9	1.199
	B	60, 60	2.0	1.239
	V	30, 30	2.0	1.260
	I	30, 30	2.0	1.267
PG 2331+055
	U	120	1.9	1.109
	B	60, 60	2.0	1.108
	V	30, 30	2.0	1.107
	I	30, 30	2.1	1.107
NGC 1348
	U	180	1.8	1.028
	B	30, 60	1.7	1.031
	V	15, 30	1.8	1.040
	I	15, 30	1.8	1.030

Figure 1: A XDSS red map of the covered region in the field of NGC 133. North is up, East on the left.