1. Introduction

New and more accurate observational determinations of masses, radii, temperatures and abundances are needed in order to improve the mass-luminosity relationship at the end of the Main Sequence. The recently developed families of evolutionary models also need new observational constraints in order to test their predictions. Masses, radii, temperatures and abundances can be derived only for double-lined eclipsing binaries with accurate light and radial velocity curves, (Popper 1980; Andersen 1991). In spite of a large observing effort done up to now, those quantities are poorly defined in the low mass range where only a few stars have astrophysical parameters calculated with the required accuracy for a detailed evolutionary modelling. With this aim, we have performed a 6 year photometric monitoring program of several late-type candidates, in order to obtain precise photometric uvby and light curves.

The candidates for our study were selected by using the following criteria:

1. late-type (late F's and G's),
2. detached systems, in order to minimise interaction problems like mass transfer.
3. orbital inclination close to , to be able to get precise magnitudes for both stars within the systems.
4. orbital period of a few days, so that the light curves could be covered in a reasonable period of time
5. sufficiently luminous to allow accurate photometry and spectroscopy.

The six systems selected were ZZ UMa, BH Vir, TY Tau, V530 Ori, V1061 Cyg and CR Cas. Particular attention has been paid to ZZ UMa for wich radial velocity curves are recently being obtained (Popper 1995) and good quality light curves were needed (Popper 1993).

ZZ UMa , is a detached, main sequence, late type, double line eclipsing binary. This system was classified as an eclipsing binary by Kippenhahn in 1955 (Geyer et al. 1955). The photographic light curve of Döppner (1962) is of Algol type, the time of minima and period are . Lavrona & Lavrov (1988) found little reflection and elipticity effects in the light curves. The secondary star was classified as a G6-G8 by Janiashvili & Lavrov (1989), which is in agreement with our preliminary analysis (Clement et al. 1993).

In this paper we present the first accurate and complete photoelectric uvby and light curves for ZZ UMa, whose light curve has been fully covered along eight different epochs. We also give details of the photometric reduction procedure and an estimation of the accuracy of the photometry, as well as the absolute photometry of the standard stars used. A complete analysis of ZZ UMa based on these data will be published separately.

Light curves of BH Vir and CR Cas were also completly covered (Clement et al. 1996, 1997a,b).

The other three systems selected were partially covered. Their light curves and analysis will be published elsewere.