Up: CCD astrometry and instrumental stars
After the publication of the HIPPARCOS catalogue, containing the
results of this astrometric mission (ESA, 1997), one can but notice
how scanty our data on visual binaries are, both from the
photometric as from the astrometric point of view.
Especially data on couples with separations in the order of a few
arcseconds do not allow to evaluate their significance, or to
make reliable statistics. It is therefore evident to us that
ground-based observations of visual double stars with
angular separations of a few arcseconds have to be continued;
CCD's (not in use for very long yet, compared to the history
of visual binary observing) provide new data of high reliability;
statistical treatment of the new observations combined with the
available old ones provides a strong tool for studying relative
proper motions and thus to decide upon the nature
of the objects
(cf.
Brosche & Sinachopoulos 1988
and Brosche et al. 1991).
The present results are a continuation of the observing programme we
initiated more than ten years ago
(Sinachopoulos 1988, Paper I).
In the discussion we shall have particular interest as to what
fraction of these relatively wide-separation stars show significant
motion after (at least) several decades.
Also compared to the previous articles in this series of papers,
the objects chosen are closer to the possibilities the reduction
technique affords, linked to the limiting seeing conditions; some
additional comments concerning the reduction procedure are given
in Sect. 3.1. Experience through all these years has shown that
CCD detectors are very much suited for these observations, as e.g.
Sinachopoulos et al. (1988) claimed.
Up: CCD astrometry and instrumental stars
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