#
The Washington Double Star Catalog

###
Brian D. Mason, Gary L. Wycoff, and William I. Hartkopf

#### Astrometry Department, U.S. Naval Observatory
3450 Massachusetts Ave, NW, Washington, DC 20392
wds@ad.usno.navy.mil

####

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

## 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 100,626 systems based on 690,251 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:

- Webb Society (4,224)
- CHARA speckle (7,122)
- Washington speckle (7,140)
- Tycho-2 (12,755)
- Tycho Double Star Catalogue (25,232)
- Hipparcos (13,141)
- Washington Fundamental Catalog (36,207)

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, as well as the USNO CCD Astrograph Catalog 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.

A comparison of the contributions of the different techniques, both in their total number and mean separation are given here. Those techniques with no measures listed are unique to the Delta-m Catalog.

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.

The ADS cross-reference has now been expanded and includes the identifier from the earlier Burnham Double Star (BDS; Burnham 1906) Catalogue as well as the later Aitken Double Star (ADS; Aitken 1932) Catalogue. BDS stars falling outside a criteria, based on magnitude and separation (and thus a likelyhood of physicality) were dropped from the ADS. Most of these stars were added back in the Index Catalogue of Visual Double Stars (IDS; Jeffers, van den Bos and Greeby 1963). Some of these stars were true binaries, and should be added back, others were added due to concerns due to common proper motion determinations or proximity. In the three cross-reference files below there are sorts based on BDS number (listing all BDS entries, even those not real though these have explanations for their removal), ADS number (again, bogus binaries carry a reason for their removal), and WDS coordinate. As before, all components associated with the BDS or ADS system are included even if they were not known at the time of the publication of those catalogs. As mentioned above, duplicate and bogus systems included in the BDS or ADS have been excised for one of the following reasons:

1. Not real. See Douglass, G.G. "The non-duplicity of 189 ADS stars," 1978, Bull. Inf. Centre Donnees Stellaires, 14, 11
2. Not in WDS. Single according to IDS notes and also in McC1984.
3. Not in WDS. In a planetary or reflection nebula.
4. In a file of Charles Worley's called "horror.data." He said, "you're going to have to deal with this, he he he." Very questionable, or would not have been purged from WDS.
5. In WDS, 1984.0 but excised from WDS, 1996.0. I don't know why. In a file of Charles Worley's called "suspect.data." I do not know what the material difference is between this and "horror.data," they may just represent problem data done at different times.
6. In WDS, 1984.0, but excised from WDS, 1996.0. Not in horror or suspect files. This could indicate its non-duplicity was certain.
7. In BDS but excised from ADS, IDS, WDS. Double not found. Purged.
8. In BDS. Removed from ADS, reinserted into IDS, removed from WDS. Apparently Aitken had it right. Purged.

Cross-reference Files
- BDS sort
- ADS sort
- WDS sort

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 4th Catalog of Interferometric Measurements of Binary Stars (Hartkopf, Mason, Wycoff, & McAlister 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.

## Unpublished Results

For a variety of reasons, there exist a large subset of measures contained in the WDS database which have not been published. To make these data available to the astronomical community they are listed below. It is anticipated that this section will expand substantially as the data contained in the WDS are collated.

#### Nils Wieth-Knudsen measures:

In late 2001, Inger Wieth-Knudsen made available to the U.S. Naval Observatory the original measurement cards Dr. Nils Wieth-Knudsen made towards the end of his distinguished career. The original cards are cataloged in the James Melville Gillis Library of the U.S. Naval Observatory. The 471 measures recorded on these cards are grouped into 211 means of 59 systems, and include 33 measures of differential magnitude. Made with both 10 and 30 inch telescopes, the observation dates range from 1961.32 to 1989.34 and the measured separations range from 0.46 to 28.97 arcseconds.

#### Walt Sanders measures:

Over the past years Walt Sanders has (and is) continuing his observing of primarily wide M dwarf stars with a filar micrometer on the Lick 36-inch refractor. This continues the work described in The Astronomical Journal (volume 71, page 1008; December 1966). As of January 1, 2002 it consisted of 219 measures averaged into 99 means of 69 pairs, with observation dates from 1996.32 to 1998.70 (thusfar, observations continue) and the measured separations range from 3.2 to 122.9. In three cases no separation is measured, but the position angle is.

#### Martin Nicholson measures:

In late 2002 Martin Nicholson began a project of examining the Guide Star Catalog for close doubles. An explanation of his project, written by him, is provided here.

#### OAG General Catalogue of 10,000 visual double stars measurements 1970-2003 (J2000.0):

Coordinated by Tofol Tobal and Jaume Planas. Garraf Astronomical Observatory. Barcelona-Spain

In the last 40 years, a limited group of Spanish amateurs has been systematically measuring visual double stars. Actually, they are preparing to publish all the measurements made between 1970 and 2001 --- over 10,000. This massive work has been presented at October, 2000, in the annual meeting of the Astronomic Society of France's Double Stars Commission, celebrated in Castelldefels, near Barcelona, Spain. (Josefina Ling, Circular UAI Commission-26 was in the meeting).

The first measurement catalogue entirely produced in Spain by an amateur was the Jose Luis Comellas (Doctor of Contemporaneous History, Sevilla University) one, published in 1973 (Catalogo de Estrellas Dobles Visuales 1973.0). It contained measurements from 1,200 double stars, using a simple micrometer and a 75mm aperture Polarex-Unitron refractor. Twelve years after, the same author published a second catalogue (Catalogo de Estrellas Dobles Visuales 1980.0) that included 5,104 doubles within reach of his new 102mm aperture Polarex-Unitron refractor, with a Ron Darbinian Filar Micrometer, of which he had personally measured over 3,500. For the quality and quantity of his publications, that included his exceptional Guia del Firmamento (1982) where he gathers together all his experience of more than thirty years of visual observation, as well for his extraordinary human condition, he is one of the most loved and admired authors in Spain and South America.

Since 1985 new observers have assured the continuity of J.L. Comellas work. Since 1976, I regularly collaborated with him, and in the mid 80s I had a little observatory supplied with a 102mm Polarex Unitron refractor and a filar micrometre, that enabled me to start systematic revision and update programs of the 1980.0 catalogue. In 1991, in conjunction with other colleagues, we coordinated the measurements sent to us by isolated observers, and started to publish a circular (RHO: Circular de Estrellas Dobles Visuales) for internal use, in order to coordinate our work and to make known our results.

Our equipment enhanced its measurement power with the purchase of new precision micrometers, Double Image Lyot-Chamichel-like, and CCD devices. Between 1992 and 2003 more than 5,000 new observations and measurements has been collected, provided by Spain-wide amateurs, and this has allowed to arrange a new catalogue suited to the 21st Century observers needs.

Given the huge bulk of filed data, it was necessary to develop our own database managing, analysis and ephemeris calculation software (MAIA). This job has been carried on by my colleague Jaume Planas, in collaboration with Jordi Cairol and Albert Sanchez, both members of OAG.

The evolution and development of this process has been made known in the meetings of the Astronomic Society of France's Double Stars Commission in Lyon (1995), Nice (1996), Bordeaux (1997), Tolouse (1999). This has enabled the Spanish visual double stars observers to break a certain isolation they were suffering since some decades ago.

Actually, the database and the different aplications it contains are for internal use only, but we are preparing an interactive version for Internet. In this way, our "OAG General Catalogue of 10,000 visual double stars measurements 1970-2000 (J2000.0)" wll be easily available to any worldwide observer.

Note about Garraf Astronomical Observatory

Garraf Astronomical Observatory (OAG), founded in 1991 from private and public investments, develops didactic and research programs. Our observatory (1992-1998) have a 3.5m diameter dome with a 300mm aperture Newton-Cassegrain (F/3,5 and F/13,5) reflector, and 150mm F/8 refractor. Is located 30km to the south of Barcelona, inside the Garraf Natural Park, 300m over the sea. Our observatory is fully equipped for a double stars programs, with CCD, Professional Double Image Lyot-Camichel Micrometer (made by MECAPRECIS-France) and various Micrometer Reticle Eyepiece (MEADE).

OAG wishes to contact and to establish research programs specialized in visual double stars with others observers and observation teams. It has accommodation facilities for up to 55 people.

(text by : Tofol Tobal, Garraf Astronomical Observatory, e-mail: rho@arrakis.es, http:// www.oagarraf.org)

Available files:
- Wieth-Knudsen measures
- Sanders measures
- Martin Nicholson description
- Martin Nicholson measures, Set 1
- OAG Files:
  - OAG Catalog
  - OAG Supplement 1
  - OAG Supplement 2
  - OAG Supplement 3
  - OAG Supplement 4
  - OAG Supplement 5
  - OAG Supplement 6
  - OAG Supplement 7

## 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:

- Separation greater than three arcseconds
- Delta-m (V band) of less than three magnitudes
- Both components brighter than 11th magnitude
- and one of three possible parameters meriting inclusion
  - Not observed in twenty years (an N code)
  - Unconfirmed (a C code)
  - Orbit system in the above parameter space, possibly useful for calibration (a * code)

A total of 6442 objects meet these criteria.

Neglected Doubles List Set I:
- Northern List (Dec > +20, num = 3072)
- Equatorial List (-20 < Dec < +20, num = 2331)
- Southern List (Dec < -20, num = 1039)

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.

Neglected Doubles List Set II:
- Northern List (Dec > +20, num = 1860)
- Equatorial List (-20 < Dec < +20, num = 2710)
- Southern List (Dec < -20, num = 2062)

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.

Neglected Doubles List Set III:
- Northern List (Dec > +20, num = 21,061)
- Equatorial List (-20 < Dec < +20, num = 11,491)
- Southern List (Dec < -20, num = 13,216)

Set three contains thirteen doubles since excised by the Tycho team. These have been marked on the observing lists.

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:

- 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). 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 1,220 newly determined (TDS = Tycho Double Star) systems from the Tycho-2 database. The previous total of 1,234 new systems, has been changed to 1,220 following retraction of some new double stars by the Tycho team. These numbers are presented as blank lines in the TDS cross reference file. 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.

In 2001 an effort led by Claus Fabricius was begun to extract from the Tycho pixel data as many double stars, both new and known, as possible. This effort has resulted in the Tycho Double Star Catalogue. A total of 25,232 additional double star measures (in addition to those enumerated above) were found. The numbering of new Tycho doubles (the TDS stars) includes the original set of 1,234 (subsequently reduced to 1,220) described above plus additional systems found in the Tycho Double Star Catalogue reduction. This second set of new doubles begins with TDS1235 (the retracted TDS numbers are not reused). A complication arose as a result of the magnitude of this work --- what to do when the number is 10,000 or more (i.e., after TDS9999, what next?). A makeshift strategy was employed by taking the next available designation, TDT (Tycho Doubles, too?), thus the next system after TDS9999 is TDT 1. The known and new doubles listings includes both analyses of the Tycho data. In addition, precise coordinates (better than arcsecond) are available for another subset of double stars seen as single by Tycho (due to the magnitude of the secondary and/or separation of the system). The improvements in the precision of the WDS is discussed below.

Available files:
- HDS vs. Hipparcos cross reference
- Hipparcos Problem Star cross reference
- Double stars measured by Tycho-2
- New Tycho-2 double star (TDS) measures

## Other Changes in the WDS

#### Changes since the WDS, 2001.0:

As the WDS is updated nightly, distinguishing the changes that have been made is not always a trivial matter for the user. Output from the unix ``diff'' command (cf., GNU diffutils version 2.7) is given below.

Available files:
- Summary Catalog differences
- Reference file differences
- Notes file differences

#### 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 6th Catalog of Orbits of Visual Binary Stars (Hartkopf & Mason 2001; hereafter, Orbit Catalog), the Speckle Catalog, and the Second 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 Second 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:

Corrections have been made to many of the Luyten duplicate designations as well as the new discoveries, since disclaimed, of the Tycho-2 project. These and other errata are provided in an error correction file which is available online.

#### 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.

Links:
- Home page of the Multi-Commission Meeting
- WMC (Washington Multiplicity Catalog) nomenclature scheme
- Text of the approved resolution

#### Duplicate Discovery Designations Removed:

One of the more difficult issues in dealing with the WDS as a database is the presence of duplicate discovery designations - that is, different systems assigned the same 3-character + 4-digit designation. These generally fall into one of two categories: systems given the same numbers but published in different lists, and those given some additional designation appended to the original one.

Examples of the first are the binaries first resolved by W. Herschel and both F.G.W. Struve and O. Struve. William Herschel published seven lists (I - VI, plus ``new'', or N), with stars of each list starting at number 1. In addition to their original discovery lists, each of the Struve's published an appendix, as well as a list of ``rejected'' doubles. These multiple lists were completely spelled out in the Aitken Double Star Catalogue (e.g., H IV 48), but when the Index (IDS) Catalogue was compiled at Lick all of these other designators were dropped for lack of space. As a result there are, for example, five components with the designation H 48! The source Herschel list was given in the notes file to the IDS. Appended and rejected stars from the lists of the Struve's were handled with an ``a'' or ``r'' towards the end of the WDS data line in most cases.

In the second (and fortunately rare) case, systems found quite near to known ones were given the same designation plus trailing character(s) (e.g., ES 1293a or BU 885 1/2). Sometimes both components were assigned these additional characters, sometimes only one; occasionally two pairs in an entirely different section of the sky were given the same designation by the author (probably by mistake).

Each of these cases is being handled in a different manner. For the William Herschel discoveries, a list identifier is added to column three of each designation. For example:

    H    19 (at 16 hours) was originally H II 19 and is now known as H 2  19,
    H     7 (at 18 hours) was originally H V 7   and is now known as H 5   7, and
    H   111 (at 06 hours) was originally H N 111 and is now known as H N 111.

In the case of the O. Struve appendix an A is added following STT in the name. For F. Struve, he provided two appendices. Those from the shorter list (Appendix II) are designated STFB. For example:

    STF  11 (appendix I)  is now STFA 11.
    STF  11 (appendix II) is now STFB 11.
    STT 252 (appendix)    is now STTA252.

Stars of the second type are given the same 3-letter discovery designation but a new number, starting with 9001, to indicate that they originally had a different designation. For example:

    BAL2356b    is now BAL9001.
    BU  885 1/2 is now BU 9001.

A complete list of stars of the second type is provided in the error correction file. All changes in designation are described in the notes file. In addition to these, designations for 271 W. Herschel (H ), 110 F. Struve (STF) and 227 O. Struve (STT) systems have been changed. Note that for some of these systems, the former three character, four digit reference (a3i4) has been replaced by a four character, three digit reference (a4i3). Although, for all USNO applications (e.g., data or observing list request) an a7 read will see no difference.

#### Arcsecond Precise Coordinates:

Coordinates which are sixty times more precise than the WDS identifier are now provided for the majority of WDS systems (i.e., tenths of a second of time and seconds of arc). Coordinates are obtained from Hipparcos, Tycho-2, the Tycho Double Star Catalogue, or through manual inspection. It is expected that the next significant improvement in this area will be when either the 2MASS or UCAC data is cross-referenced with the WDS. Incremental changes will continue to be made as well. The ten-digit WDS identifier is retained and will continue to be the same for all components in hierarchical systems. However, the precise coordinate will be for the primary of the subsystem. For example, in the case of a system made up of A-BC and BC pairs, they will both have the same ten-digit WDS identifier, however, the fourteen digit precise coordinate would be of the A and B component, respectively. As of 14 December 2004 arcsecond precise coordinates had been found for 92% of the systems in the WDS (i.e., 93,073 systems). We give here grateful acknowledgement to all those who have assisted us in locating these many of the hardest to find pairs: Richard Jaworski and John Greaves.

#### Secondary Proper Motion:

The most common note (N = 1421) in the WDS notes file was the proper motion of the secondary, when known. The above matching with Tycho-2 has allowed the determination of secondary proper motion for 37% of the WDS (as of 1 July 2002, matching continues; i.e., 36,042 systems). The secondary proper motion is found following the precise position. This is expected to grow considerably when the UCAC is complete.

#### The Bright Star list (H2-H31) of the Astronomical Almanac:

Stars found in the Bright Star list of the Astronomical Almanac have been cross-referenced with both the WDS and the single star list (described below). Those which have matches with the WDS have their most recent observables (position angle, separation, delta-m) along with other identifiers. All known resolved components of bright stars are listed. Stars found in the Bright Star list which match with the single star list are listed by HR number only. These stars are indicated as single by

- large aperture speckle which resolves down to 60 milliarcseconds for components with delta-V less than 3, and
- are not Hipparcos ``problem stars'' (G, X, V, or O codes in field H59 of the main catalog or S code in field H61).
- Further, they are not in the WDS, which has many binaries listed not detected by speckle interferometry according to the parameters listed above.

Available files:
- Double Stars in the Bright Star list
- Single Stars in the Bright Star list

For double stars in the above list, if the last measured separation is less than 0.05 arcseconds, a separation of `<0.1' is listed. If the magnitude of the listed component is unknown, this is reflected in the delta-m column, which is also unknown.

## 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 stars show no indication of duplicity in any of the three catalogs,
- the stars have tabulated null detections in the Speckle Catalog, at least one of which was obtained with a telescope of 2-m or greater aperture, and
- the stars have no Hipparcos double-star solutions (C, G, X, V, or O codes in field H59 of the main catalog) and no S (``suspected non-single'') code in field H61.

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

- ### WDS Catalog (~10.1Mb)

  - 00-06 hour section (~2.1Mb)
  - 06-12 hour section (~2.9Mb)
  - 12-18 hour section (~1.9Mb)
  - 18-24 hour section (~3.2Mb)
  - Format of the current WDS
  - Notes file for the WDS (~1.1Mb)
  - References and discoverer codes (~0.7Mb)

    ####
    Supplemental Files:

  - Synonyms to the Notes file
  - Error Correction file
  - Top Twenty-five Observers list
  - Statistical comparison of different techniques

  ####
  Cross References:

- BDS vs. ADS vs. WDS : BDS sort
- BDS vs. ADS vs. WDS : ADS sort
- BDS vs. ADS vs. WDS : WDS sort
- HDS vs. Hipparcos cross reference
- Hipparcos Problem Star cross reference
- Double stars measured by Tycho-2
- New Tycho-2 double star (TDS) measures

####

Neglected Doubles

List Set I:
- Northern List (Dec > +20, num = 3072)
- Equatorial List (-20 < Dec < +20, num = 2331)
- Southern List (Dec < -20, num = 1039)
- Finder Charts for Lists I
  List Set II:
  - Northern List (Dec > +20, num = 1860)
  - Equatorial List (-20 < Dec < +20, num = 2710)
  - Southern List (Dec < -20, num = 2062)
  List Set III:
  - Northern List (Dec > +20, num = 21,061)
  - Equatorial List (-20 < Dec < +20, num = 11,491)
  - Southern List (Dec < -20, num = 13,216)

  #### Additional Files:

- Double Stars in the Astronomical Almanac Bright Star list
- Single Stars in the Astronomical Almanac Bright Star list
- Single Star list

  #### Links:

  - Home page of the Multi-Commission Meeting
  - New WDS nomenclature scheme
  - Double Star Library
  - Double Star Astronomy at the USNO
  - USNO Publication Page
  - WDS, 1996.0
  - WDS, 2001.0
  - Current WDS
  - Sixth Orbit Catalog
  - Calibration Systems
  - Fourth Interferometric Catalog
  - Second Photometric Magnitude Difference Catalog

  ## 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 custom observing list, a copy of the Double Star CD, or make a comment by e-mail.

  - Data Request form
  - Observing List Request form
  - Double Star CD Request form
  - Comment form

  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.

  ## References

  - Aitken, R.G. 1932, New General Catalogue of Double Stars within 121 degrees of the North Pole, Carnegie Institution of Washington
  - Barton, S.G. 1926, AJ 36, 155
  - Burnham, S.W. 1906, General Catalogue of Double Stars within 121 degrees of the North Pole>, Carnegie Institution of Washington
  - ESA 1997, The Hipparcos and Tycho Catalogues (ESA SP-1200) (Noordwijk: ESA)
  - Fabricius, C. & Makarov, V.V. 2000, A&AS, 144, 45
  - Fabricius, C., Hoeg, E., Makarov, V.V., Mason, B.D., Wycoff, G.L., & Urban, S.E. 2002, A&A, 384, 180
  - Hartkopf, W.I., Mason, B.D., & Worley, C.E. 2001, AJ, 122, 3472
  - Hartkopf, W.I., McAlister, H.A., & Mason, B.D. 2001, AJ, 122, 3480
  - Hoffleit D., Warren, Jr., W.H. 1991, The Bright Star Catalogue, 5th Revised Ed., (Preliminary Version)
  - Innes, R.T.A. 1927, Southern Double Star Catalogue, -19 to -90 degrees, Union Observatory, Johannesburg, South Africa
  - Jeffers, H.M. & van den Bos, W.H. 1963, Index Catalogue of Visual Double Stars, 1961.0, Pub. of the Lick Observatory, 21
  - Mason, B.D., Wycoff, G.L., Hartkopf, W.I., Douglass, G.G., & Worley, C.E. 2001, AJ, 122, 3466
  - Morlet, G., Salaman, M., & Gili, R. 2000, A&AS, 145, 67
  - Worley, C.E., & Douglass, G.G. 1984, Washington Visual Double Star Catalog, 1984.0, U.S. Naval Observatory, Washington
  - Worley, C.E., & Douglass, G.G. 1997, A&AS, 125, 523 (Washington Visual Double Star Catalog, 1996.0
  - Worley, C.E., Mason, B.D., & Wycoff, G.L. 2001, AJ, 122, 3482
  - Wycoff, G.L., & Mason, B.D. 2001, (in preparation)

  This page is maintained by Brian Mason

  Updated: 14 December 2004

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