1 Introduction

The investigation of binary stars is a key to many problems of modern astrophysics. Visual double stars, which represent the tail of longest orbital periods in the distribution of binaries in general, are in fact poorly studied so far. Although they have been observed for about two centuries, their physics and, in most cases of wide pairs, even the question of "opticity" of the companions are still under discussion.

This work is a part of the extended investigation of visual double stars with primaries of spectral class A. The aim is to obtain reliable statistics of the photometric properties of their components. These data are required in the frame of determination of their evolutionary status and possible mechanisms of formation. Investigation of newly obtained precise astrometric information may also help to reject optical pairs by comparison of their relative motion with the possible orbital one [12, (Russel & Moore 1940)].

For this purpose we selected the binaries of class A from the Washington Double Stars catalogue [15, (Worley & Douglass 1984], hereafter WDS), which have separations in the range from 2 to 8 arcsec. These limits were set by the resolution capabilities of the available observational technique from one point and by the desire to have a moderately low rate of optical pairs from the other. In general there is no photometric information on primary and secondary components separately and no recent astrometry. So, the new data will improve our knowledge of the physical nature of these moderately young wide binaries.