Assessment of the accuracy of measures in the 1829 southern double star catalogue of James Dunlop

In 1829 James Dunlop published the first southern double star catalogue of some 253 double stars. The accuracy of this catalogue has been determined by using Aladin to cross-match them with Gaia DR2 and estimate their positional (right ascension, declination, position angle, and separation) and magnitude accuracy. Seven per cent could not be identified using Aladin and 14 were single stars. We found 13 double stars (5 per cent) not currently listed in the Washington Double Star Catalog. The catalogue equinox was determined as B1826.0. Overall, 1 sigma uncertainties in right ascension were within 1 sidereal minute and declinations within 10 arcmin. We also identified and corrected a number of Quadrant errors in the position angles and quantified the separations. Apparent visual magnitude estimates were generally within 1 mag. Dunlop's overall uncertainties were larger than those of his contemporaries, nevertheless the little known catalogue remains valuable as the earliest source of over 200 double star astrometric and visual magnitude estimates.