Conclusions
·
We have used observational data from the Washington Double Star (WDS) catalog to assess
the proper motions listed in the Hipparcos and Tycho-2 catalogs for a small set of stars that are
members of wide, bright double systems. The set of stars was selected to ensure that any
nonlinear component of orbital motion was be negligible for the time span of the observations.
·
The data showed that, overall, the WDS data tended to favor the Tycho-2 proper motions over
those from Hipparcos for this set of stars, although this trend might be mostly due to fewer
"outliers" in Tycho-2 than Hipparcos. For many double systems, it may be possible to use the
WDS data to improve the proper motions of the individual components, given some simple
assumptions.
·
By using three independent data sources, estimates of the external errors of the proper motions
can be obtained. The errors derived in this way are ~3.5 mas/yr for Hipparcos, ~2.5 mas/yr for
Tycho-2, and 12 mas/yr for WDS. These values are subject to many qualifications, but are
not inconsistent with the respective formal errors for the subset of stars analyzed here. At the
very least, they undoubtedly correctly rank the three catalogs for the reliability of their proper
motion information for our subset.
·
The Hipparcos data for our subset of stars, all members of wide double systems, are sub-
stantially poorer than that for the single stars in the catalog. This may be due to observational
difficulties that occurred when more than one bright star was in the Hipparcos field of view.
