CCD photometry and astrometry for visual double and multiple stars of the HIPPARCOS catalogue^*

III. CCD photometry and differential astrometry for 253 southern "intermediate" systems

¹ Koninklijke Sterrenwacht van België, Ringlaan 3, 1180 Brussel, Belgium e-mail: patricia.lampens@oma.be
² Observatoire de Besançon, 41 bis, avenue de l'Observatoire, BP 1615, 25010 Besançon Cedex, France e-mail: oblak@obs-besancon.fr

Corresponding author: P. Lampens, patricia.lampens@oma.be

Received: 26 June 2000
Accepted: 11 April 2001

Abstract

We present new astrometric and photometric data for 253 visual double stars of the "intermediate" class, i.e. with angular separations in the range 1 to 15 arcsec. The multi-colour observations were obtained in 1992-94 as part of the ESO Key Programme "Visual Double Stars" performed at La Silla Observatory (Chile). Differential magnitudes and colours have been secured in a systematic way while component magnitudes and colour indices have been determined in the V and I passbands of the Cousins standard system in good photometric conditions only. Internal and mean external errors are smaller than respectively 0.01 mag and a few hundreths of a magnitude (typically less than 0.03 mag). Relative positions are obtained as a by-product with internal errors of the order of 0.006´´in angular separation (corresponding to pixel width ) and 0.07°in position angle. Final accuracies are thoroughly discussed: we illustrate the overall excellent quality of the data and estimate the quality degradation for angular separations barely larger than the width of the seeing disk.