Double Star Products
Since the mid 1960s, when the Index Catalogue of Double Stars was transferred from Lick Observatory to the US Naval Observatory, the resultant catalog, redesignated the ``Washington Double Star'' (WDS) Catalog, has been the official double star catalog of Commission 26 (Double and Multiple Stars) of the International Astronomical Union (IAU). Maintained online in summary form, this catalog lists the first and last observation parameters for every known pair in the sky. On demand we provide every catalogued measure: 1,030,959 measures of 118,558 measured pairs (as of 1 August 2012; database is updated nightly), varying from 1 to 1679 measures per system (mean = 7.25, median = 3). Using the resources of the USNO Library, extensive catalog work has been done to include all available measures from 1690 to the present day. Notes to individual systems are also provided. We also, on demand, can prepare custom observing lists suited to the observing capabilities and desires of observers worldwide.
This catalog lists what has been characterized as the best available orbit of a pair. Published orbits exist for 2,518 of the WDS pairs (as of 11 September 2014) and determining which one of possibly several published solutions is best has been done by an objective numerical grading scheme (described in the catalog text). ORB6 also includes ephemerides giving predicted positions for the next several years, orbital plots of all WDS data on the calculated orbit, as well as a separate list of "calibration-quality" orbits which are adequate for most scale and orientation determinations.
This catalog is the most recent addition to the suite of double star catalogs maintained at the USNO. Using some of the same methods used to generate ORB6, this catalog lists rectilinear elements for 1,494 pairs (as of 22 May 2015) whose motion is fit adequately by a straight line. While it is possible that some of these may be physical doubles with a very long period and perhaps high eccentricity, most are likely optical pairs whose differential proper motion can be linearly characterized. As double star observations have been made for a longer time and often with greater frequency than classic astrometry techniques, many of these pairs have differential proper motions determined to greater precision and accuracy than can be done by other, more conventional, methods.
This catalog enumerates all measurements of double stars made by high resolution techniques. These include interferometry as well as adaptive optics, satellite observation, lunar occultation as well as other methods enumerated in the catalog notes. Complete photometric information, when available, is also provided, as are interferometric "single star'' detections. These stars have been examined for close pairs and no similar brightness pair has been found to the listed limit. These single stars are then appropriate for scale determination (with other equipment) or point source characterization.
This catalog lists all measures of magnitude difference made by precise techniques. The magnitude difference and the color in which it is determined, can aid in the determination of a companion's spectral type. If one or both of the components is variable, this can aid in the characterization of the variability.
In addition to this suite of double star catalogs, work is in progress on the Washington Multiplicity Catalog (WMC). Approved at a Multi-Commission Meeting at IAU General Assembly XXIV (Manchester, 2000) and re-affirmed at a Special Session at IAU General Assembly XXV (Sydney, 2003), the WMC is a designation scheme which will hierarchically arrange all double stars detected by multiple techniques: astrometry, spectroscopy, photometry and other methods.
While not a double star catalog, the USNO also maintains the Double Star Library (DSL), an eclectic collection of links, announcements, and other data of relevance to double star astronomers. The DSL served as the official webpage of IAU (International Astronomical Union) Commission 26 (double and multiple stars) for many years, and still provides a link to new IAU commission pages, as well as to the Commission G1 Information Circular, its official tri-annual publication.