Up: Mining in the Hipparcos data
Most of the new solutions given in the following sections were made
possible because of the availability of several pieces of information
that were not used during the data processing for lack of time,
or simply because the information did not exist at that time or was overlooked.
Essentially, the new data consists of updated values for the relative
astrometry and/or photometry of double stars.
As mentioned above
the grid step error could be avoided if a good a priori
separation and position angle could be secured to select the most
likely solutions among the two or three possible. It is worth
emphasising that for the vast majority of the double stars solved from
the Hipparcos data, the processing was self-sufficient and did not
need to rely on a good starting point. Only when the double
star signal was too weak or the observation equations poorly
conditioned was the starting value more crucial.
This concerned only a small
fraction of the
Hipparcos double stars, but a large fraction of the subset reinvestigated in
this paper.
Several sources were used to reprocess the Hipparcos observations of
the selected doubtful solutions:
- The Tycho Catalogue includes components of wide binaries
(
arcsec) observed as two independent entries provides they are
brighter than
V = 10.5. From the individual astrometric solutions it was easy to
derive the separation and position angle of the two components.
- For each of the suspected binaries not solved from the
Hipparcos data, we have systematically extracted a field from the
Digitized Sky Survey, either from the first or second epoch. When
the separation between the two components is larger than about 5
arcsec this was easily detected as an elongated image or two well-defined
stellar images. A rough measurement was sufficient to
provide a reliable input for
and
which was then used for the
starting value in the Hipparcos double star software.
Figures 1-2 show two examples taken
respectively from the
the first and second epoch of the Digitized Sky Survey.
- In some cases the Input Catalogue provided valuable
information not fully exploited during the automatic data
processing essentially because of the complexity of sorting out the components
of
the multiple systems, a practical problem which did not fit easily within a
mass
processing with stringent
time constraints.
- Finally recent CCD observations of visual
double stars yielded updated or new astrometric parameters for
several systems (Cuypers et al. 1998; Lampens et al. 1998;
Oblak 1998).
 |
Figure 1:
Example of a binary system (HIP 34707) measured over a field of arcsec from the STScI Digitized Sky Survey (1st epoch) and showing
well detached
components. A crude measurement in the image gave
and
deg. From the Hipparcos observations one gets respectively
and 183.8 deg |
 |
Figure 2:
Example of a binary system (HIP 21000) measured over a field of arcsec from the STScI Digitized Sky Survey (2nd epoch) near the
lower limit
of resolution. A crude measurement in the image gave
and
deg. From the Hipparcos observations one gets respectively
and 289 deg |
Up: Mining in the Hipparcos data
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