Sixth Catalog of Orbits of Visual Binary Stars William I. Hartkopf & Brian D. Mason U.S. Naval Observatory, NW, Washington, DC Note: The following description is adapted from a paper by Hartkopf et al. (2001 AJ 122, 3472.) The "Sixth Catalog of Orbits of Visual Binary Stars" continues the series of compilations of visual binary star orbits published by William Finsen, Charles Worley, and Wulff Heintz from the 1930s to the 1980s. As of 27 July 2017 the new catalog included 2,739 orbits of 2,656 systems. All orbits have been graded as in earlier catalogs, although the grading scheme was modified as of the "Fifth Catalog" to be more objective. Ephemerides are given for all orbits, as are plots including all associated data in the Washington Double Star (WDS) database. A subset of orbits potentially useful for scale calibration is also presented. INTRODUCTION The "Sixth Catalog of Orbits of Visual Binary Stars" (henceforth "Sixth Catalog"; Hartkopf et al. 2001a) continues the series of compilations of visual binary star orbits previously published by Finsen (1934, 1938); Worley (1963); Finsen & Worley (1970); Worley & Heintz (1983, henceforth "Fourth Catalog"); and most recently by Hartkopf, Mason, & Worley (2001b, henceforth "Fifth Catalog"). The 17 years between publications of the Fourth and Fifth Catalog saw revolutionary changes in the field of visual double star work, primarily through the advent and maturation of interferometry. Speckle interferometry, especially on large telescopes, can produce astrometric results of very high accuracy (down to milliarcsecond level), even for systems much closer and of shorter period than those available to micrometry and other visual techniques. Although the speckle technique has been known since 1970, it did not produce data in significant quantity until about 1975; at the time of publication of the Fourth Catalog only a handful of orbits had been calculated in which speckle played much of a role. Now, however, speckle interferometry is a mature field, and nearly all orbits published since the 1980's have included speckle results, some exclusively. Long-baseline interferometry [e.g., Mark III (cf., Pan et al. 1990) and the Navy Prototype Optical Interferometer (NPOI; cf., Hummel et al. 1998)] is now perhaps in a similar degree of maturation as was speckle in 1983; an increasing number of binaries once exclusively the 'property' of spectroscopists are now the targets of multi-aperture telescope arrays. Indeed, the distinction between the 'spectroscopic' and 'visual' regimes will largely disappear in the coming decades, as the magnitude sensitivity of these new interferometers improves. Catalogs such as this will have to evolve as well; as spectroscopic + visual 'combined solutions' go from being rare to commonplace, the argument for publishing only a subset of a binary's elements will grow increasingly artificial. For the present, however, information on combined solutions is relegated to a notes file. GRADING THE ORBITS A major consideration in the production of a new catalog is the determination of grades for each orbit. See the Sixth Catalog website (http://ad.usno.navy.mil/wds/orb6.html) for a full description of the grading scheme used. DESCRIPTION OF THE CATALOG The 'master file' for the Sixth Catalog includes all sets of orbital elements in the Fourth Catalog, as well as all subsequently published orbits either tabulated by Worley or found through searches of the literature from 1980 through the present. Several older catalogs, including those of See (1898), Lewis (1906), and Finsen & Worley (1970) have been added for historical purposes; others are being incorporated as time permits. This file included 8,406 orbits of 2,656 systems as of 27 July 2017. All orbits were graded, and only those judged of highest grade for each system were included in the published Sixth Catalog. If two orbits for a given system were judged to be of nearly identical quality, the earlier-published orbit was chosen for the catalog (although both are kept if the orbits were contemporaneous). A few systems were found to have two very different sets of orbital elements which yielded comparable grades; in these cases both orbits were included. These 'special cases' bring the total number of orbits in the Sixth Catalog to 2,739. The Web allows much more flexibility than is available in a paper catalog such as the Fourth Catalog, so we have added several extra columns of information, as well as figures and ephemerides. In the web version, names and orbital elements for a given system are tabulated on two lines, with a blank line separating each orbit for ease in reading. However, for the text version the information for each orbit is given on a single line, for ease of sorting or program input. The format of this text version is given in the file orb6format.txt. Catalog statistics and other information are also available on the orbit website. ACKNOWLEDGMENTS Thanks foremost to the U.S. Naval Observatory for four decades' worth of support for the authors' double star observing and cataloging efforts. Thanks also to Drs. Wulff Heintz and the late William Finsen, without whose efforts this series of catalogs would never have existed. This catalog has made use of the SIMBAD database. We dedicate this catalog to the memory of Charles Edmund Worley, our colleague and friend. REFERENCES Boden, A.F. et al. 1999, ApJ 527, 360 Douglass, G.G., Hindsley, R.B., & Worley, C.E. 1997, ApJS, 111, 289 Eichhorn, H. & Cole, C.S. 1985, Celestial Mechanics 37, 263 Finsen, W.S. 1934, Union Obs. Circ. 4, 23 Finsen, W.S. 1938, Union Obs. Circ. 4, 66 Finsen, W.S. & Worley, C.E. 1970, Republic Obs. Circ. 7, 203 Harrington, R.S. 1992, 'A Review of Dynamical Studies of Multiple Stars', Complementary Approaches to Double and Multiple Star Research, ASP Conf. Ser., Vol. 32, IAU Colloq. 135, H.A. McAlister & W.I. 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