UBVabsolute CCD photometry and differential astrometry of a sample of visual double stars with A-type primaries ***

We present Vmagnitudes, $({\it B}-{\it V})$and $({\it U}-{\it B})$colours of the components of 111 visual double stars and their relative position measurements ρ and θ. The primaries are of spectral class A; the angular separation is in the $2\hbox{$.\!\!^{\prime\prime}$}5-8^{\prime\prime}$range. The observations were made at the 61-cm reflector of University of Toronto Southern Observatory, Chile. The obtained photometric results are of a moderate quality for absolute values ($0.04^{\rm m}$(mag) in Vand about $0.02^{\rm m}$in the $({\it B}-{\it V})$and $({\it U}-{\it B})$colour indices) and more precise in $\Delta {\it V}$and $\Delta ({\it U}-{\it B})$, $\Delta ({\it B}-{\it V})$($0.023^{\rm m}$and $0.015^{\rm m}$, respectively). We find that about 60% of secondaries are also of spectral type A; 56% of pairs have $\Delta({\it B}-{\it V})$less than $0.1^{\rm m}$. The two-colour diagram reveals significant offset of objects from the curve of unreddened Main Sequence stars. A comprehensive survey of stars in the close vicinity to the objects is also presented. The final astrometric accuracy of $\approx 0\hbox{$.\!\!^{\prime\prime}$}01$in ρ and $0\hbox{$.\!\!^{\circ}$}1$in θprovides additional measurements for study of relative motion of the components.