The SuperCOSMOS Sky Survey - III. Astrometry

Abstract

In this, the third in a series of three papers concerning the SuperCOSMOS Sky\nSurvey, we describe the astrometric properties of the database. We describe the\nalgorithms employed in the derivation of the astrometric parameters of the\ndata, and demonstrate their accuracies by comparison with external datasets\nusing the first release of data, the South Galactic Cap survey. We show that\nthe celestial coordinates, which are tied to the International Celestial\nReference Frame via the Tycho-2 reference catalogue, are accurate to better\nthan +/- 0.2 arcsec at J,R=19,18 rising to +/- 0.3 arcsec at J,R=22,21 with\npositional dependent systematic effects from bright to faint magnitudes at the\n+/- 0.1 arcsec level. The proper motion measurements are shown to be accurate\nto typically +/- 10 mas/yr at J,R=19,18 rising to +/- 50 mas/yr at J,R=22,21\nand are tied to zero using the extragalactic reference frame. We show that the\nzeropoint errors in the proper motions are < 1 mas/yr for R > 17 and are no\nlarger than 10 mas/yr for R < 17 mas/yr.\n