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 percent 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, 1σ uncertainties in right ascension were within 1 sidereal minute and declinations within 10 arcminutes. We also identified and corrected a number of Quadrant errors in the position angles and qualified the separations. Apparent visual magnitude estimates were generally within 1 magnitude. 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.

The relative Rectilinear motion of optical double stars provides an important clue to the relationship of the components. We provide an objective method of confirming the optical status of double stars, and of obtaining unbiased rectilinear elements solely on data obtained from the HIPPARCOS and Gaia DR2 space missions. We apply this technique to determine the rectilinear elements of 14 optical double stars from the southern double star catalogue of James Dunlop.The resultant uncertainties are, on average, an order of magnitude smaller than the method currently used.

Binary double stars are those whose binding energies are less than zero. Obtaining binary star orbits from short arcs has been a long-standing problem in astrophysics. A method is presented and tested here, which addresses the problem by using space-based astrometry, photometry, and astrophysical data, together with historic measures, to generate and constrain a range of possible first-order Grade 5 orbits. After testing the method on an established binary star, we apply the method to eight double stars from the first published catalog of southern double stars, that of Dunlop (1829) and generate orbits for five. The mean orbital period is ∼81,000 years, and the mean semi-major axis is ∼76 ′′ with a typical uncertainty of the Orbital Elements of ∼37%. Their Orbital Elements and associated plots are also presented.

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