1. Addressing confusion in double star nomenclature:
The Washington Multiplicity Catalog
William I. Hartkopf & Brian D. Mason
U.S. Naval Observatory
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2. A Welcome “Problem” New observing and reduction techniques 
New classes of companions (e.g., brown dwarfs, exoplanets)
Previously distinct classes (e.g., “visual” and “SB”) now observable by multiple techniques
Future interferometers, astrometric satellites, etc means the problem will become worse!
Result is greater understanding for the scientist, but greater challenges for the cataloger!
U.S. Naval Observatory

3. So What IS the Problem?
Different techniques mean different nomenclature!
Visual binaries: “discoverer designations” (e.g., S or STF 1413, b or BU 96)
Spectroscopic binaries: HD, etc.
Eclipsing binaries: variable star designation
Occultation binaries: SAO, ZC
Multiple method may yield multiple designations
Component confusion! One person’s AB pair may be another’s ab or BA or primary/secondary!
U.S. Naval Observatory

4. Addressing the Problem
Informal working group (1999) came up with four suggested schemes:
KoMa (D. Kovaleva & O. Malkov): Alphabetic, numeric and Roman numerals to indicate hierarchy and companion type
UC ( S. Urban & T. Corbin): numeric scheme similar to library call numbers
Sequential (L. Dickel & P. Dubois): components assigned numbers in order of discovery
WMC (Washington Multiplicity Catalog): based on upper/lower case letters of WDS, with extensions
U.S. Naval Observatory

5. Addressing the Problem, II
IAU Symposium 200: WMC favored. Sequential scheme deemed sufficiently different from others for further discussion.
IAU-GA XXIV: methods for clearing up nomenclature ambiguities discussed. WMC endorsed and Class C resolution ratified by Commissions 5 (Documentation & Astronomical Data), 8+24 (Astrometry), 26 (Double & Multiple Stars), 42 (Close Binary Stars), and 45 (Stellar Classification):
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6. On Designating Components of Binary/Multiple Star Systems
Recognizing
the increasing synergy of techniques for the investigation of stellar companions blurring the traditional distinction between astrometric,spectroscopic, and photometric binary and multiple stars;
the detection of substellar (including planets) as well as stellar components by these techniques and,
the need for a simple, unambiguous, flexible, and computer friendly designation scheme for components of binary and multiple star systems,
Noting that future ground and space-based telescope projects have the potential to detect both substellar as well as stellar components in increasingly large numbers,
Recommends that
a uniform designation scheme, based on expansion of the new WDS system, be developed during the next 3 years to include all types of components and that this be reviewed in time for its adoption to be considered at General Assembly XXV.
U.S. Naval Observatory

7. Implementation Present sample of resulting scheme at Colloquium 191.
MODIFY!
Present modified scheme to SOC of IAU-GA XXV Special Session 3: A New Classification Scheme for Double Stars.
MODIFY AGAIN!
Present further modified scheme at SPS3, July 18, 2003.
If approved, present all-sky WMC at 2006 GA.
Continue updates to WMC.
U.S. Naval Observatory

8. Roots of the WMC
WDS: principal database of visual double and multiple star data for the astronomical community
Maintained at USNO, updated nightly
597,579 measures for 99,284 pairs (as of Feb 2003)
Delta-m catalog: differential magnitudes not in WDS
Orbit Catalog: 1,692 systems
Interferometric Catalog: 138,532 high-res observations for 53,063 stars
U.S. Naval Observatory

9. Applying WDS rules to the WMC
WDS lists all resolved systems. Many components are detected but not resolved, however:
spectroscopic doubles (SB1 and SB2),
photometric or eclipsing binaries,
astrometric doubles,
lunar occultation doubles,
other doubles,
planets, other substellar objects
WDS nomenclature rules (with slight modification) can accommodate all types of double stars.
U.S. Naval Observatory

10. WDS and Hierarchy WDS is system-based rather than object-based.
For object-based scheme, N objects  N entries
For system-based WDS, N objects  up to N(N-1)/2 entries
WDS also contains measures between photocenters.
Multiple systems may become quite complex as N increases. However, WDS lists only pairings actually measured. Observers’ common sense usually implies system hierarchy.
WDS also includes measures of optical pairs.
U.S. Naval Observatory

11. Determination of Hierarchies
Hierarchy based on orbital period and/or separation. The 3:1 ratio of semi-major axes (R.S. Harrington) generally followed. Exceptions:
Separations >1” usually given upper-case letters.
3:1 ratio assumes physicality. However, most visual doubles do not have enough measures to determine whether motion is Keplerian or rectilinear. Assume all double stars within some small separation are of interest.
U.S. Naval Observatory

12. Rules of Component Designation
WDS nomenclature handles second level hierarchies.
WMC will cover more complex systems:
Level 1  capital letters
STF1523 AB
Level 2  lower case letters
FIN 347 Aa,Ab
Level 3  numbers
ORD 666 Ba1,Ba2
Higher levels  alternate lower case letters and numbers
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13. Component Designation, II
Delimiter: comma, with full component identifier before and after (e.g., Aa,Ab). Exceptions:
Assume “A,B” if no designation
(e.g., A = A A,B).
Delimiter assumed if only two characters
(e.g., WAK 8 CD = WAK 8 C,D).
WMC will strive to maintain hierarchies, but this is not always possible, given often very limited knowledge. We’ll do the best we can!
If a subsystem cannot be assigned unequivocally, a tentative “best guess” assignment will be given and a note added to the catalog.
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14. Illustrating a Complex System
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15. The Sample WMC
RA = 11h – 11h30m band. Historically compelling (“home” of x UMa), and has a variety of component types:
astrometric binaries,
X-ray binaries, cataclysmic variables, related objects,
eclipsing binaries,
occultation binaries,
spectroscopic (SB1 + SB2) and spectrum binaries,
interferometric binaries,
visual binaries, and
planetary companions (by extending to 10h59m.5 …)
U.S. Naval Observatory

16. Sources of Multiplicity
WDS and other USNO double star catalogs
Downes et al. 2001, “A Catalog and Atlas of Cataclysmic Variables: On-line Version”, PASP 113, 764 (
Ritter & Kolb 1998, “Catalogue of cataclysmic binaries, low-mass X-ray binaries , and related objects (Sixth edition)”, A&AS 129, 83
Batten et al, 1989, “Eighth Catalog of the Orbital Elements of Spectroscopic Binary Systems”, Pub. DAO, v. 17
Pourbaix et al., 2003, “Ninth Catalogue of Spectroscopic Binary Orbits” (
Svechnikov & Bessonova 1984, “Catalog of Orbital elements, Masses and Luminosities of close double stars”, Bull. Inf. CDS 26, 99
van Paradijs 1995, “A Catalogue of X-Ray Binaries”, in ‘X-ray Binaries’, Lewin et al, eds., Cambridge Univ. Press, ch. 14, p
California & Carnegie Planet Search website ( and links
Other sources needed!
U.S. Naval Observatory

17. Contributions by Technique
Techniques contribute to the sample WMC as follows:
95.8% = visual binaries and optical pairs,
50.6% = interferometric binaries and optical pairs,
1.7% = spectroscopic binaries,
1.4% = cataclysmic variables or related objects,
1.0% = occultation binaries,
0.3% = astrometric binaries,
0.2% each eclipsing binaries and X-ray binaries,
0.1% each spectrum binaries and planets.
Techniques are complementary, so sum is >100%.
U.S. Naval Observatory

18. Coordinate Matching
System matches are based on stars’ arcsecond precise coordinates. The most time-consuming aspect of the WMC construction (by far!) was the improvement of the WDS’ arcminute coordinates:
80% matched to Hipparcos or Tycho-2.
additional 19% matched to GSC2, USNO A2, 2MASS, etc. via individual inspection using ALADIN.
1.3% (21 pairs) still have only arcminute accuracy coordinates. Nearly all are older, unconfirmed, visual doubles (very wide cpm pairs or suspect coordinates).
U.S. Naval Observatory

19. Sample Statistics
The 1,465 systems in this slice of the sky may be broken down as follows:
1,336 (91%) simple binaries
80 (5.5%) non-hierarchical triples
16 (1.1%) non-hierarchical systems, >3 components
25 (1.7%) hierarchical triples
8 (0.5%) hierarchical systems, >3 components
U.S. Naval Observatory

20. Explanation of the Columns
= WMC designation (WDS or J2000 arcminute coordinates)
= component designation (AB; Aa,Ab; etc.)
= name (HD, DM, variable star desig., discoverer desig., etc.)
= name (Tycho-2, GSC2, USNO A2, 2MASS, etc.)
= angular separation (vector sep, predicted from SB, etc.)
= orbital period
7, 8 = magnitudes (filter codes if not V, flags for variability)
9,10 = spectral types
= parallax (from Hipparcos, orbital parallax, etc)
12,13 = masses (or mass function, mass ratio. etc.)
= binary type (visual, spectroscopic, etc.)
= references (with web links)
= J2000 arcsecond coordinates
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21. WMC Page 1
Text
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22. WMC Page 2
Text
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23. Int 4 Page
Text
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24. Orb Page 1
Text
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25. Orb Page 2
Text
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26. SB9 Page
Text
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27. CCV Page
Text
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28. CCP Page
Text
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29. Sample WMC Examples U.S. Naval Observatory
WMC Comp ?? NAME Sep....* Period.y Mag1.f Mag2.f Spec Spec2...
AB CD
AC CD
AB * 47 UMa y G0V planet
AC * 47 UMa y G0V planet
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30. Sample WMC Examples U.S. Naval Observatory
WMC Comp ?? NAME Sep....* Period.y Mag1.f Mag2.f Spec Spec2...
Aa,Ab HD K
Aa,B HD K
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31. Sample WMC Examples U.S. Naval Observatory
WMC Comp ?? NAME Sep....* Period.y Mag1.f Mag2.f Spec Spec2...
Aa,Ab ** GHE k k ?e
AB ** GHE k k ?e
Ab1,Ab2 ** BNK k k
AC ** SZR k k ?e
U.S. Naval Observatory

32. Sample WMC Examples U.S. Naval Observatory
WMC Comp ?? NAME Sep....* Period.y Mag1.f Mag2.f Spec Spec2...
AB HD A2V
AC HD A2V
AD HD A2V K0
AE HD A2V
AF HD A2V
AG HD A2V
U.S. Naval Observatory

33. Sample WMC Examples U.S. Naval Observatory
WMC Comp ?? NAME Sep....* Period.y Mag1.f Mag2.f Spec Spec2...
Aa,Ab * xi UMa d G0V M3V?
AB HD y G0V F8.5V
AC HD G0V
Ba,Bb * xi UMa m d F8.5V planet?
Ba,Bc HD F8.5V K2-3V?
U.S. Naval Observatory

34. Sample WMC Examples U.S. Naval Observatory
WMC Comp ?? NAME Sep....* Period.y Mag1.f Mag2.f Spec Spec2...
Aa,Ab HD
Aa,Ac HD
Aa,Ad HD WN WN...
AB HD WN WN...
AC HD WN
AD HD WN
AE HD WN
U.S. Naval Observatory

35. Help!
Your suggestions needed (format, information to add or delete, etc.). See WMC website (link from WDS website:
is arcminute-accuracy WMC designation sufficient?
should planet designations be different?
Your data are needed (for WDS, Orb6, SB9, etc as well!) send comments, etc. to or
U.S. Naval Observatory