CR Cas was observed in three observational campaigns. The telescope used was the 1.5 m reflector of the Centro Astronómico Hispano-Alemán at the Calar Alto Observatory (Almerıa, Spain). The telescope was equipped either with a multipurpose one-channel photoelectric photometer (Lahulla & Pensado 1981), or with a four-channel photometer (Florentin-Nielsen 1983), both using u, v, b, and y filters as well as narrow and wide H

filters. The 377 points for the light curves, which cover the primary minimum at least three times and the secondary twice, were obtain in the following nights:

The instrumental system and transformation equations were computed separately for each individual run, following the procedure described in detail by Grønbech et al. (1976). In order to determine the atmospheric extinction, every night a set of 2 to 4 standard stars were observed more than four times at air masses ranging from 1 to 2. In each observing run mean zero points were computed for the whole period, before determining the nightly extinction coefficients. Their mean values for the 18 nights considered,

and

for y, (b-y), m₁ and c₁ respectively, show the good behaviour of the atmosphere during those nights. We also determined the night corrections L(n) within each observing period in order to obtain the magnitudes in the instrumental system. No significant variations between nights were found.

After extinction and night corrections, instrumental magnitudes were transformed to the Crawford & Barnes (1970) and Crawford & Mander (1966) standard systems. The standard stars were selected from the lists of Perry et al. (1987) and Olsen (private communication). A detailed description of the photometric reduction procedures, and an estimation of the accuracy of the photometry for the program campaigns can be found in Clement et al. (1997).

SAO 35044 and SAO 35197 were used as comparison and check star respectively for differential photometry. Its constancy was checked every night. Internal RMS errors of 0.009, 0.005, 0.014, 0.023, and 0.010 in y, (b-y), m₁, c₁ and

for the 181 differences (SAO 35044 - SAO 35197) are of the same order as for the program objects and show no variability for the comparison stars during the period of observations. Due to the fact that the comparison stars are of different spectral type than CR Cas, they are not good matches for differential photometry, and some uncertainty due to extinction effects could be present in the differential light curves.

The differential magnitudes (CR Cas - SAO 35044) are listed in Table 4. Figures 1 (click here), 2 (click here), 3 (click here) and 4 (click here) show the differential light curves in each band. It is noticeable some level of variability at the bottom of the primary eclipse, mainly in the u and v bands. Moreover, the

index is highly variable at all phases, with a dispersion at least three times higher than for the other stars measured in the same observing periods. This two facts led us to suggest that the secondary star could be an emission-line star (Clement et al. 1996), although no spectroscopic confirmation is available yet.

Photometric magnitudes and indices for the comparison stars and for CR Cas at eclipses and first quadrature are listed in Table 1 (click here).

	CR Cas	SAO 35044	SAO 35197

	34' 06''	27' 05''	00' 05''
Sp. type	B0.5V + B1V	G8IV	G5
V (0.25)	11.281	8.232	9.155
	4	6	25
V (0.00)	12.182
	5
V (0.50)	11.710
	2
(b-y) (0.25)	0.503	0.646	0.583
	4	1	6
(b-y) (0.00)	0.511
	13
(b-y) (0.50)	0.495
	6
m₁ (0.25)	-0.104	0.345	0.276
	10	2	6
m₁ (0.00)	-0.087
	32
m₁ (0.50)	-0.122
	11
c₁ (0.25)	0.114	0.389	0.326
	9	7	11
c₁ (0.00)	0.272
	34
c₁ (0.50)	0.092
	24
(0.25)	2.606	2.573	2.554
	6	2	13
(0.00)	2.607
	16
(0.50)	2.602
	1

Table 1: Standard photometry for CR Cas and the comparison stars

2. The observations