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Astronomical Applications Department, U.S. Naval Observatory - pm AAS poster (Page 7)

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Astronomical Applications Department, U.S. Naval Observatory - pm AAS poster
The Sample
Since this was a pilot study to evaluate whether WDS data were appropriate for proper motion
evaluations, we were conservative in the sample of stars selected for study. In particular, we
wanted double star systems that were likely to have very long periods compared to the span of
WDS observations, which in some cases was a century and a half. Furthermore, we wanted stars
with good data in all three catalogs. Our selection criteria were:
A component m
< 8, B component m
< 11
At least 15 observations in WDS
Most recent measured separation > 10 arcsec
Difference between first and last measured separations < 5 arcsec
Independent proper motion determinations for A and B in Hipparcos (double entry systems)
No systems known to have more than 2 components; no pathological stars

The result was 162 bright double systems, with an average visual magnitude of about 7 for the
A components and 8 for the B components. Other statistics for this sample are shown in the plots
to the right. Based on the parallaxes of components, over 4/5 of these double systems may be
physical pairs, although crude estimates of the periods (actual orbits and periods are unknown)
indicate that they are in fact so long that nonlinear orbital motion is negligible compared to the
uncertainties in the data.

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