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Han (1989, AJ 97, 607) has shown that the precision of astrometric estimates of the separation of two star images, measured at the Allegheny Observatory, may be approximated by the expression:
SE = 0.140$\(S/600)^{0.33}$ / $\(t)^{0.5}$
where S is the separation in arc seconds, and t is the integration time of the measurement. Han's measurements, acquired with the Multichannel Astrometric Photometer (Gatewood, 1987, AJ 94, 213), showed that the atmospheric turbulence theory of Lindegren ( 1980, AA 89, 41) was valid over separations of 330 to 1260 arc seconds. Han and Gatewood (1995 PASP may issue) have conducted a similar study using photographically acquired star trails to show that the first constant in the above equation is 0.054 at the Mauna Kea site. Using small fields on large telescopes at excellent sites may lead to astrometric precision an order of magnitude better than now obtainedby astrometric instrumentation (Gatewood, 1991, BAAS 23, 1433). Using a CCD camera on the Allegheny Observatory's 0.76 m Keeler astrometric reflector we have extended the study of the astrometric effects of turbulence at the site to angles smaller than 30 arc seconds. The result of observations, with integration times of 0.1 to 3.0 seconds, as well as the effects of various CCD centering algorithms are reported.
