Astronomical Applications Department, U.S. Naval Observatory pm AAS poster Page 1
An Independent Assessment of a Subset of
Hipparcos and Tycho-2 Proper Motions
George H. Kaplan and Sabrina C. Snell
U.S. Naval Observatory
Abstract:
The positions, proper motions, and parallaxes of 10
5
stars in the Hipparcos main catalog, derived
from satellite data taken in the early 1990s, define the International Celestial Reference Frame at
optical wavelengths. The Tycho-2 catalog is a 25
×
densification of the Hipparcos system,
combining data from the Hipparcos satellite with those from a large number of ground-based
astrometric catalogs produced over the last century. Tycho-2 proper motions have been
previously shown to be comparable, in the aggregate, to those in Hipparcos (Urban et al. 2000)
for stars in common.
In this pilot study, we assessed the external accuracy of the proper motions for a selected subset
of stars in the Hipparcos and Tycho-2 catalogs, using an independent source of data, the
observational measures recorded in the Washington Double Star Catalog (WDS). The selected
