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

We present V magnitudes, (B - V) and (U-B) colours of the components of 111 visual double stars and their relative position measurements rho and theta . The primaries are of spectral class A; the angular separation is in the 2 ".5 - 8" range. The observations were made at the 61-cm reflector of Univer sity of Toronto Southern Observatory, Chile. The obtained photometric resul ts are of a moderate quality for absolute values (0.04(m) (mag) in V and ab out 0.02(m) in the (B - V) and (U - B) colour indices) and more precise in Delta V and Delta(U-B), Delta(B - V) (0.023(m) and 0.015(m), respectively). We find that about 60% of secondaries are also of spectral type A; 56% of pairs have Delta(B - V) less than 0.1(m). The two-colour diagram reveals si gnificant offset of objects from the curve of unreddened Main Sequence star s. A comprehensive survey of stars in the close vicinity to the objects is also presented. The final astrometric accuracy of approximate to 0".01 in r ho and 0 degrees.1 in theta provides additional, measurements for study of relative motion of the components.