# Introduction

The Washington Double Star Catalog (WDS) maintained by the USNO is the world's principal database of astrometric double and multiple star data. 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 83,211 systems based on 500,129 means.

# Changes in the Current Version

#### Changes due to Hipparcos:

The current edition of the WDS contains the most recent, observational data available and includes systems newly discovered by the Hipparcos satellite. While Hipparcos did not provide discovery designations these are the primary system identifier in visual double star astronomy. A cross reference file of these 3,406 systems containing the abbreviated coordinate, as well as the HDS and HIP numbers is provided. A cross reference 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 pseudo-confirmation) are indicated in the notes file.

#### Changes due to Tycho-2:

The current version of the WDS also contains measures of 7,485 systems from the Tycho-2 Catalogue. These include 6,251 known systems from the Tycho-2 Catalogue as well as 1,234 newly determined (TDS) systems from the Tycho-2 database. Photometric information has been updated for systems not resolved by Hipparcos. Also, notes have been added for 2,757 systems of dubious veracity (N < 3) having a "failed double" or "photocenter" solution.

#### The Delta-m Catalog:

Also, new to the WDS is an additional indicator in columns 100-102. This ``D'' note code indicates the system has a separate Delta-M determined (in addition to those determined during astrometric measures). These results, primarily from Charles Worley's Delta-m catalog plus other lunar occultation and interferometric determinations 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.

# Additional Information Available

#### 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 can 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 easier said than done. Generally speaking, the more stars are studied the higher their multiplicity fraction. What is believed to be a good single star can render vital calibration data useless through the discovery of a previously unknown double star or the slight modification of the psf by an unresolved component.

The basic data for this list comes from the ``Third Catalog of Interferometric Measures of Binary Stars'' (Hartkopf, W.I., McAlister, H.A., & Mason, B.D. 2000). In addition to publishing measurements of double stars from speckle and Michelson interferometry, and lunar occultation measures, this also contains results from various duplicity surveys (n = 3,632). Selected stars from this catalog which are also found in ``The Bright Star Catalogue'' (D. Hoffleit & W. Warren, 1992, Fifth Revised Edition, preliminary) with a published null detection from a telescope with an aperture greater than two meters are then considered (n = 1,769). This list is then of bright stars which have no indication of duplicity by speckle interferometry. Any of these objects which have measures by other techniques in the 3rd Catalog (either interferometry or lunar occultation) are also excluded, as are systems which have entries in this current version of the WDS.

Further, all of these systems were observed by the Hipparcos Satellite (ESA 1997, The Hipparcos and Tycho Catalogues, ESA SP-1200), and they do not have any double star solution (C, G, X, V, or O in field H59 of the main catalogue) nor are they ``suspected non-single'' (S code in field H61).

The final all-sky list contains 1,170 systems fulfilling these criteria.

#### ADS Stars:

Due to its continued use, a cross reference file from the ADS to the WDS discovery designation and abbreviated coordinates is provided here.

#### Multi-Commission Meeting on Stellar Designations:

The aim of this meeting (scheduled for Thursday, August 10, 2000 during the XXIVth General Assembly of the International Astronomical Union) is to develop a simple, unambiguous, flexible, and computer friendly designation scheme for stellar companions (including planets). The home page of the multi-commission meeting is here.

# USNO Double Star Publications

Recent results from the USNO double star program are available here. These papers present results from the speckle measurement series, the orbit series, other refereed papers, as well as oral and display presentations from meetings.

# Concluding Remarks

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.

A preliminary version of the 5th Orbit Catalog to this site soon.

####

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.

- The Current WDS Catalog (~8.6Mb)
  - 00-06 hour section (~1.9Mb)
  - 06-12 hour section (~2.4Mb)
  - 12-18 hour section (~1.6Mb)
  - 18-24 hour section (~2.8Mb)
- The format of the current WDS
- The main Notes file for the WDS
- The synonyms to the Notes file
- The Discoverer codes and publication references
- The Additional Discoverer codes
- The HDS vs. Hipparcos cross reference
- The WDS vs. Hipparcos Problem Star cross reference
- The WDS vs. ADS cross reference
- The Single Star list
- WDS Request form
- WDS Comment form

You may request a reasonable amount of information from the double star catalog by e-mail.

This page is maintained by Brian Mason

Approved by F. Stephen Gauss, Astrometry Department, USNO

Updated: 28 January 2000

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