A Study of the Accuracy of Narrow Field Astrometry using Star Trails taken with the CFHT

Abstract

We extend the study of Han (1989, AJ, 94, 213) to angles as small as 7 arcsec. To investigate the relation between the relative-image motion and the separation of two stars in astrometric observations, we analyzed star-trail plates taken with the CFHT by Christian and Racine (1985, PASP, 97, 1215). The result shows that on Mauna Kea the rms relative-image motion for 1 s of integration time is given by sigma=0.054 arcsec (theta/10 arcmin)(0.35), where theta is the separation between two stars. The standard theory on atmospheric turbulence predicts that sigma is proportional to the one-third power of theta. Our study shows that it is valid for the range of 7 arcsec