Astron. Astrophys. Suppl. Ser. 139, 69-74

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

N. Shatsky¹² - D. Sinachopoulos¹ - P. Prado³ - E. van Dessel¹

Send offprint request: N. Shatsky

Correspondence to: kolja@sai.msu.su

1 - Royal Belgian Observatory, Ringlaan 3, B-1180 Brussels, Belgium
2 - Sternberg Astronomical Institute, Universitetskii pr. 13, Moscow 119899, Russia
3 - European Southern Observatory, La Silla, Chile

Received January 4; accepted May 5, 1999

Abstract:

We present V magnitudes, $({\it B}-{\it V})$ and $({\it U}-{\it B})$ 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 $2\hbox{$.\!\!^{\prime\prime}$}5-8\hbox{$^{\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 V and 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 $\rho$ and $0\hbox{$.\!\!^\circ$}1$ in $\theta$ provides additional measurements for study of relative motion of the components.

Key words: stars: binaries: visual -- techniques: photometric -- astrometry