The Washington Double Star Catalog, 2001.0

Brian D. Mason, Gary L. Wycoff, William I. Hartkopf, Geoffrey G. Douglass, and Charles E. Worley

Astrometry Department, U.S. Naval Observatory
3450 Massachusetts Ave, NW, Washington, DC 20392,,

If we are free to wish, we ought to have two large reflectors, one in the North and one in the South, devoted to discovery and measures of double stars.

If we look back for a century or more and ask: What do we today appreciate mostly of the observations made then? the general answer will be: observations bound to time. They can, if missed, never be recovered. Of these observations measures of double stars contribute a major part.

As far as we can judge today this will also be the case in the future.

The search for new double stars should be made with the largest instruments available in order to discover close and faint companions.

--- Ejnar Hertzsprung to Charles Worley, April 2, 1965

These files are no longer updated. This is an archival website for the 2001.0 edition of the Washington Double Star Catalog. The last major update to this site was 26 September 2001 by Brian Mason.

Introduction and Growth of the WDS

The Washington Double Star Catalog (WDS), maintained by the United States Naval Observatory, is the world's principal database of astrometric double and multiple star information. The WDS Catalog contains positions (J2000), discoverer designations, epochs, position angles, separations, magnitudes, spectral types, proper motions and when available, Durchmusterung numbers and notes for the components of 84,486 systems based on 563,326 means. The current version, available online, is updated nightly. This catalog is one of four USNO double star catalogs to be included on a CD-ROM now in preparation. A brief summary and statistical analysis of the contents of the catalog are presented.

The Washington Visual Double Star Catalog (WDS) is the successor to the Index Catalogue of Visual Double Stars, 1961.0 (IDS; Jeffers & van den Bos, 1963). Three earlier double star catalogs in this century, those by Burnham (BDS; 1906), Innes (SDS; 1927), and Aitken (ADS; 1932), each covered only a portion of the sky. Both the IDS and the WDS cover the entire sky, and the WDS is intended to contain all known visual double stars for which at least one differential measure has been published. The WDS is continually updated as published data become available. Prior to this, two major updates have been published (Worley & Douglass 1984, 1997). The Washington Double Star Catalog (WDS) has seen numerous changes since the last major release of the catalog. The application of many techniques and considerable industry over the past few years has yielded unprecedented gains in both the number of systems and the number of measures, as indicated below.

Figure 1: Growth in the number of means in the WDS since its inception in the early 1960's. The 1984.0 and 1996.0 editions of the WDS are indicated and at the cutoff date for the CD-ROM production.

The growth since the 1996.0 edition is due to many sources, however the most significant additions are:

While many thousand new systems have been added, many of these observing programs have resulted in a striking improvement in the number of observations per system, as shown below with a specific example of USNO speckle contributions. It is expected that with other large publications of data planned in the future [e.g., the Two Micron All Sky Survey, the USNO CCD Astrograph Catalog, as well as further Tycho reduction (Fabricius et al. 2001)] the growth of the WDS will continue.

Figure 2: The number of means per system in the WDS. The left figure is a histogram from late 1997 (the WDS 1996.0 with Hipparcos added) while the right figure illustrates the same information for the 2001.0 version of the WDS. Note that while the total number of systems has increased by more than 6300, the number of systems with only one mean has dropped by more than 1700.

Figure 3: One source responsible for the increase in data is the prodigious publication of USNO speckle means. The left figure illustrates a histogram of USNO speckle means (also late 1997) binned vs. separation. The right figure indicates the same information for the 2001.0 version of the WDS.

Primarily of historical interest, a list of the top 25 observers (based on the total number of measures and means) is presented here. In this table, numbers are based on the WDS reference code. Totals are provided for the number of means (usually, as published --- a line of data in the WDS measurement database, each mean position often comes from several measures, usually increasing their accuracy).To the extent that it is known, multiple authors participating in a distinct group or project are counted together.

One of the largest listings in both lists above is the Washington Fundamental Catalog (WFC; Wycoff & Mason 2001). These double star measures were extracted from the WFC, a collection of 144 astrographic and transit circle catalogs covering a timebase of over one hundred years and most recently used in the computation of proper motions for the Tycho-2 project. While not intended as a double star reference, the utility of transit circle and photographic measures were known early in the 20th century, and many of the doubles in the Astrographic Catalogue were previously gleaned by Barton (1926) and others. However, there remained a plethora of double star measures in these catalogs which have now been cross-referenced with the WDS to produce these totals.

Due to their historical importance and their continued use, a cross reference file from the ADS (Aitken 1932) to the WDS discovery designation and abbreviated coordinates is provided online here. In this file, all components associated with the ADS system are included even if they were not known at the time of the publication of the ADS. Duplicate and bogus systems included in the ADS have been excised.

Some detections are not included in the WDS. These include measures by long baseline interferometry where only visibilities and baselines are published (as opposed to a true separation and position angle) are not included. Also, various 1-d detection data (e.g., lunar occultation and some infrared speckle interferometry) are not included, as the measured separation is only a projection of the true separation. These data are available in the 3rd Catalog of Interferometric Measurements of Binary Stars (Hartkopf, McAlister, & Mason 2001; hereafter Speckle Catalog). The absence of separation and position angle information for the long-baseline interferometry data is perhaps most tragic as these data cannot be readily combined with other ``classical'' double star data for a true combined solution.

Neglected Doubles

A large number of systems in the WDS may be characterized as ``neglected.'' These include unconfirmed binaries as well as systems which have not been resolved for many years. The reasons for this neglect are varied: poor coordinates or large proper motion (so the systems are ``lost''), erroneous magnitude or delta-m estimates (so the systems are skipped over or misidentified), or true neglect (too many binaries and too few observers). While the veracity of some of these systems is certainly suspect, many (if not most) of these are bona fide double stars. Three sets of lists are provided in observing list format. The first set was compiled using the following selection parameters:

A total of 6442 objects meet these criteria.

Finder Charts for List Set I

The second set of lists were compiled under the same criteria as above, but for separations under 3 arcseconds. A total of of 6632 systems fit these criteria.

The third and final set of lists includes those neglected systems not covered by the previous lists. These include systems with large magnitude differences, or fainter primary or secondary magnitudes, as well as systems whose magnitudes or separations are either unknown or unpublished. A total of 45,768 systems fit these criteria.

These lists, especially the last, can be tailored to your specific observing needs. To have a custom-made observing list prepared with parameters different than those above, please fill out an observing list request form:

Hipparcos and Tycho-2

The current edition of the WDS contains the most recent, observational data available and includes systems newly discovered by the Hipparcos mission. While Hipparcos did not provide discovery designations, these are the primary system identifiers in visual double star astronomy. A cross reference file of these 3,406 systems first resolved by Hipparcos (HDS = Hipparcos Double Star) containing the abbreviated coordinate, as well as the HDS and HIP numbers is provided as are cross references of WDS entries which had Hipparcos problem solutions (i.e., the G, X, O, V double star solutions as well as those which were suspected non-single) is also available. Systems with only one measure in the WDS which are Hipparcos problem stars (thus, providing a quasi-confirmation) are indicated in the notes file.

The current version of the WDS also contains measures of 12,770 systems from the Tycho-2 Catalogue. These include 11,536 known systems as well as 1,234 newly determined (TDS = Tycho Double Star) systems from the Tycho-2 database. Also, notes have been added for 1,130 systems of dubious veracity (N < 3) having a ``failed double'' or ``photocenter'' solution. Some of these are being reconsidered as further processing of the Tycho-2 data for double stars continues (Fabricius et al. 2001). A cross-reference of double stars measured by Tycho-2 is available here. A cross-reference of new TDS systems is available here.

Other Changes in the WDS

Changes in the reference file:

The reference file appears in a different format than previously available. In the past, three characters would specify to whom the reference belonged with a two digit number indicating the specific reference. In the case of some observers, this was proving inadequate. The problem was exacerbated by the fact that the WDS, the 5th Catalog of Orbits of Visual Binary Stars (Hartkopf, Mason, & Worley 2001; hereafter, Orbit Catalog), the Speckle Catalog, and the Photometric Magnitude Difference Catalog (Worley, Mason, & Wycoff 2001; hereafter Delta-m Catalog) all used different reference codes. A new reference file is therefore provided which gives the new code as well as the WDS reference code, followed by the reference. This is expected to change over time as the WDS is reformatted and the old WDS catalog code is replaced. The additional discoverer codes are included within this file.

Changes in the data request software:

The data request software has been rewritten and the output is in a new format which is (hopefully) more user-friendly. Also, the software now searches the Delta-m Catalog and the Orbit Catalog in addition to the WDS. Over time we will be adding other features in a data request package.

In addition, we now also provide custom-made observing lists. If the user provides limitations as to RA, Dec, separation, magnitudes, number of observations, and date of last observation, it is possible to prepare observing lists. Both data requests and observing list requests are available online.

The Delta-m Catalog:

New to the WDS is an additional indicator in columns 100-102. This ``D'' note code indicates the system has additional Delta-m information tabulated in the Delta-m Catalog (in addition to those determined during astrometric measures). These results will eventually be incorporated in a weighted scheme for the magnitude listings of the WDS data line.

Discovery Designations Added:

The coordinates provided for entries in the WDS are neither unique nor constant, and are therefore, unsuitable to identify a system. Following the assignment of HDS designations to systems first resolved by the Hipparcos satellite, an effort was made to assign unique discovery codes to all other systems in the WDS. In some cases, two different systems can have the same discovery code and number but different components. Therefore, to uniquely identify a system it is necessary to include the component field. Eight hundred twenty-two systems have had their discovery number assigned by the USNO in this manner and are identified in the notes file.

Systems Removed:

Forty-seven pairs of systems have been identified as being equivalent. Many of these were first identified by Fabricius et al. (2001) while working on the Tycho-2 double star reduction project. Notes to the systems which are retained also indicate the alternate designations. These and other errata are provided in an error correction file which is available online. Many other systems remain to investigate as potential identical systems, as noted by Morlet, Salaman, & Gili (2000), Fabricius & Makarov (2000), and others.

Future of Designations:

On 11 August, 2000, during the XXIVth General Assembly of the International Astronomical Union, a Multi-Commission Meeting (MCM) on Stellar Designations was held. The purpose of this meeting was to develop a simple, unambiguous, flexible, and computer-friendly designation scheme for all stellar companions (including planets). Members from nine supporting commissions participated and, as a result, a C type IAU Resolution was drafted and adopted by Commissions 26 and 42, and later ratified by Commissions 5 and 8+24 at their respective business meetings. Subsequent to the MCM on 24 October, Commission 45 SOC members unanimously supported the resolution.

Single Stars

For observations of double stars it is often necessary and beneficial to observe single stars. These can serve as an idealized point-source-function (psf) to determine the behavior of various elements in the optical chain, characterize various reduction algorithms, or be used to generate artificial double stars or other more complicated morphologies by use of calcite crystals, slit masks, aperture masks, etc.

Unfortunately, finding a good list of these calibrator sources is more difficult than it sounds. Generally speaking, the more that stars are studied the higher their multiplicity fraction. Erroneously labeled ``single stars'' can render vital calibration data useless through the discovery of a previously unknown companion or the slight modification of the psf by an unresolved component.

The basic data for this list come from the Speckle Catalog, which tabulates null detections from various duplicity surveys in addition to double star measures obtained by speckle interferometry and other high-resolution techniques. Stars from the Bright Star Catalog (Hoffleit & Warren 1991) are checked against the WDS, the Speckle Catalog, and the Hipparcos Catalog (ESA 1997) and only considered to be ``single'' stars if all the following criteria are met:

The final all-sky list contains 1,170 systems fulfilling these criteria. In the future, it is planned to update this list to include systems which would be unresolved by optical interferometry.

The Catalog

Measures in the Washington Double Star Catalog have been collected, collated, and maintained since the early 1960's when the original IDS (Jeffers & van den Bos, 1963) was transferred from Lick Observatory to the U.S. Naval Observatory. Presented in order are the WDS J2000 coordinates, the discovery and component designation, the first and last measured epoch, the number of means, the first and last measured position angle (theta) in degrees, the first and last measured separation (rho) in arcseconds, the magnitudes of the primary and secondary, the spectral type of one or both components (if known), proper motion in RA and Dec (milliarcseconds/yr), the Durchmusterung (DM) number (The DM of the object in the system used by the Henry Draper Catalogue: Bonn from +89 to -22 inclusive, Cordoba from -23 to -51 inclusive, Cape Photographic from -52 to -89 inclusive), and a notes column. It should be noted that the WDS is not a photometric or spectral type catalog, and while the catalogers strive to provide the most correct values for these parameters, they should not be considered definitive. Some characters in the notes column indicate specific entries in another file (i.e., an N indicates an entry in the notes file), catalog (an O in the Orbit Catalog, and a D in the Delta-m Catalog), or are referenced in the format file. The full Catalog (8.7Mb) is available below as are format, note, reference and other ancillary files. The WDS 2001.0 is also available on a CD-ROM of USNO double star catalogs. Copies of this CD-ROM can be obtained from the authors.

Available Files and Links

Additional Files:

  • Single Star list

    Requests and Acknowledgements

    Addition of the delta-m information as well as other more significant changes to the WDS database is currently under consideration. The input from regular users of the database and other interested parties is greatly appreciated in our efforts to make the WDS as helpful and user-friendly as possible. Please provide comments on the format of the WDS, missed references, or any other items of interest to you on our Comment form.

    Information is being added to the database on a continuing basis, and this edition of the WDS will also be updated regularly.

    You may request a reasonable amount of information from the double star catalog, a copy of the Double Star CD, or make a comment by e-mail.

    We are in debt to Geoff Douglass for his work on the WDS database and his leadership in the speckle program at the USNO. The Washington Double Star Catalogs and USNO speckle program were conceived and nurtured by Charles Worley. Providing data in WDS format (or at least electronic format) has allowed the WDS to grow significantly. We would here like to acknowledge the contributions of Bob Argyle, Wulff Heintz, Elliott Horch, Josefina Ling, Francisco Manuel Rica Romero, and Walt Sanders.

    Concluding Remarks

    If the WDS and associated databases were helpful for your research work, the following acknowledgement would be appreciated:

    ``This research has made use of the Washington Double Star Catalog maintained at the U.S. Naval Observatory.''

    A notification of references to relevant papers is appreciated.


    This page is maintained by Brian Mason

    Approved by Theodore Rafferty, Astrometry Department, USNO

    Updated: 26 September 2001

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