Specifications concerning designations
for astronomical radiation sources outside the solar system
How to refer to a source or designate a new one from the Working Group Designations of IAU Commission B2
Contents
| Short title: | IAU Recommendations for Nomenclature |
| Key words: | Designations IAU |
| (Version August 2018) |
A look at the current literature reveals that unclear, ambiguous or confusing designations of astronomical sources of radiation are too often encountered. Therefore, all contributors to databases, and authors of papers, catalogs and surveys, are urged to adhere to the following set of specifications (developed and endorsed by the International Astronomical Union); otherwise, significant data may be irretrievably lost.
1. General recommendations
All source listings should always contain positional information and/or a second designation next to a principal designation in order to avoid ambiguities that can arise with a single designation.
2. Case of existing designations
- When existing designations are used in listings, they should
never be altered (e.g., neither truncated, nor rounded, nor shortened).
- In a publication, the bibliographical reference for the designation should be given.
3. Creation of new designations
The designation of an astronomical source should consist of the following parts :
Note that the ^ is used here to denote a blank. It is used for emphasis in showing where spaces occur in a designation. (Users are expected to use an actual blank and not this character.) Parentheses are required if a specifier is included. Acronym and sequence are essential, specifier is optional; the number of blanks may be larger in machine-readable files to right justify numerical or tabular data.
The following examples illustrate the recommended form of astronomical designations :
NGC^205
PKS^1817–43
CO^J0326.0+3041.0
H2O^G123.4+57.6^(VLSR=–185)
3C^196
3.1 Acronym
The acronym (earlier called origin) is a code (i.e., alphanumerical string of characters) that specifies the catalog or collection of sources. It may be constructed from catalog names (e.g., NGC, BD), the names of authors (RCW), instruments or observatories used for large surveys (VLA, IRAS, 3C, 51W), etc – see helpful hints on creating acronyms.
The following rules apply to the construction of new acronyms:
- an acronym shall consist of at least three characters.
- an acronym shall consist of letters and/or numerals only; special
characters, including superscripts, subscripts, Greek letters, ...
are not allowed. Blanks and punctuation marks should be avoided.
- an acronym must be unique (verify in the
Dictionary of Nomenclature); i.e., the appropriate
reference literature should be checked to avoid duplication with existing
catalog designations.
- constellation names, abbreviations of source types
(see Object classification in SIMBAD) should be avoided.
- Avoid excessively long acronyms.
3.2 Sequence
The sequence (or numbering) is an alphanumeric string of characters, normally only numerical, that uniquely determines the source within a catalog or collection. It may be a sequence number within a catalog (e. g., HD^224801), a combination of fields, or it may be based on coordinates. The way the sequence is constructed is called the format of the sequence; the symbols used are summarized in the Inventory of the Formats, a document which also includes examples of use and misuse.
3.2.1 Use of coordinates
Coordinate-based designations are just ``names'' and should have enough significant figures to unambiguously identify the sources. It is expected that precise coordinates will be provided in the paper (e.g., in a table), accompanied by any needed explanations and other relevant information. When sexagesimal coordinates are used, the right ascension portion must have one significant digit more than the declination portion. For decimal degree coordinates, RA and DEC should contain the same number of significant figures.
The number of significant digits in the sequence must not exceed the accuracy of the positions, e.g., subarcsecond positions should not be used in the sequence when the positional uncertainty is no better than an arcminute.
If coordinates in any form are used to encode a source of radiation, a set of rules applies, which we will illustrate with a source, namely the QSO with coordinates:
(J2000.0)
00h51m09.38s –42° 26' 33.8'' = 012.78908 –42.44272
(B1950.0)
00h48m48.97s –42° 42' 52.1'' = 012.20404 –42.7144
- A designation involving only the coordinates, often improperly
referred to in the literature as an ``IAU designation'', is
not sufficient to identify a source unambiguously. An acronym
should also be given.
- Equatorial Coordinates shall always be preceded by J
if they are for the standard equinox of J2000.0 (i.e., IRCS
position or FK5-based, Julian equinox 2000.0 system). They should be preceded by
B if they are for the old standard equinox of B1950.0 (i.e.,
Bessel-Newcomb FK4-based, Besselian equinox 1950.0 system). Galactic coordinates
shall be preceded by a G. The absence of a code at the beginning of
recognizable equatorial coordinates will be interpreted, by default, as a
missing B.
Ex: QSO^004848–4242.8 = QSO^B004848–4242.8 = QSO^J005109–4226.5
A galactic-based designation is inappropriate for extragalactic sources such as a QSO. Examples of galactic-based designations for sources within the Milky Way Galaxy may be found in section S3 (Ex. H2O) and section S3.5.1 (Ex. PN).
- The ``flag'' letters J, B, and G have a special
role: the flag letter should immediately precede the coordinates and should be
separated from the acronym by a space
(^). This space is
particularly important, as there are acronyms ending with J, B, and G. The usage
of other ``flag'' letters is discouraged.
- Coordinates shall contain leading zeroes (in RA and
Dec) and the plus or minus sign : +BB.bb or
–BB.bb, +DDMMSS.s or –DDMMSS.s
- Coordinates shall be specified as LLL.ll+BB.bb or
LLL.ll–BB.bb for galactic coordinates, and as
HHMMSS.ss+DDMMSS.s or HHMMSS.ss–DDMMSS.s for equatorial
coordinates (without spaces); more or fewer fractional digits may be
used as appropriate, but one should not omit the leading HH or
±DD. Coordinate names expressed in decimal degrees and J2000 should
also explicitly include the J.
Ex: QSO^004848–4242.8 could have been designated by QSO^0048–427 or QSO^0048–42
- Coordinates using an even number of digits (in either RA or
Dec), fewer than seven, are expressed in the sexagesimal system. The
sequences HHMM.mm or DD.dd where mm and dd
are decimal parts of a minute or degree, respectively,
should be avoided. If the number of digits is odd and fewer than six, the
right-most digit represents a decimal part of hours, degrees or minutes
(as, e.g., in the PKS–style HHMM+DDd or in IRAS source
designation HHMMm+DDMM) and not tens of minutes or seconds
(e.g. the formats HHMMS or +DDM should be avoided). If the
number of digits is more than six, the digits in excess of six are decimal part
of seconds of time for RA or of angle for Dec ; explicit use of
the decimal points is encouraged (e.g., HHMMSS.ss or
DDMMSS.s).
- Coordinates shall be truncated (not rounded), thus defining a unique
(small) field on the sky in which the source is located. The truncation should
also operate when the right-most digit represents a decimal part. The right-most
digit of the field HHMMm should be computed as m=int(SS/6). The
same should be done when transforming from +DDMM to DDd (as in
the PKS-style) with d=int(MM/6).
Ex: QSO^004848–4242.8 could be named QSO^00488–4242 but not QSO^00484–4242 (wrong truncation of RA) nor QSO^00488–4243 (rounded Dec).
Care should be taken to ensure that minutes and seconds do not exceed 59, sexagesimal hours do not exceed 23, and declination degrees do not exceed 89 (except exactly on the pole). Decimal degree right ascension cannot exceed 359.
- Designations that include coordinates shall be treated like proper names;
therefore, they shall not be changed even if the positions change or
become more accurately known.
Ex: BD^+25^9 stays, even though its declination has now changed to +26 degrees due to precession from its original position (at the 1855 equinox).
3.3 Specifier
Although obsolete, the specifier was optional and allowed one to indicate other source parameters. However, they were not required syntax and were enclosed in parentheses.
3.4 Punctuation and special characters
If the designation requires the use of punctuation or special characters, the recommendations are the following:
- [^]
(blank character) should be used as separator rather than a ``.'',
or ``/''.
- [_] (underscore) may be used in place of a blank, if necessary,
such as within an electronic catalog where blanks would be problematic.
- [–] should be reserved for the minus sign as much as
possible. However, if there is no ambiguity with the minus sign, it may be
used as a separator although such usage is discouraged.
- [.] should be reserved for a decimal point.
- [/] (slash) should be used for concatenation of the sources
quoted.
Ex: DR^21/23 refers to DR^21 and DR^23, not (DR^21, DR^22, DR^23)
- [:] should be reserved to indicate subdivision (subcomponent).
If, at some stage, subcomponents or multiplicity of sources is recognized, the current practice is to name the subcomponents with letters or numerals such as W 51 A. Alternatively the subcomponent receives a standard designation which may be added to the sequence of the parent source with a colon; e.g., ABELL^1644:[D80]^053 where D80 refers to Dressler's catalog of morphological types in 55 rich clusters of galaxies (1980ApJS...42..565D). For further elaboration on designating subcomponents and also on finding the reference to a subcomponent refer to current practices regarding subcomponents.
3.5 Examples
3.5.1 Examples of complete designations
| Designation | Position | |
| Acronym^Sequence^(Specifier) | RA(J2000.0) | Dec(J2000.0) |
| h m s | ° ' '' | |
| RX^J1426.8+6950 | 14 26 49.3 | +69 50 21 |
| HESS^J1302–638 | 13 02 47.72 | –63 50 08.5 |
| PN^G001.2–00.3 | 17 49 36.9 | –28 03 59 |
| TYC^1234–545–1 | 03 32 53.6417 | +15 32 59.314 |
| 1E^2127+119 | 21 29 58.312 | +12 10 02.67 |
The examples in the table above are from pre-existing designations. A look at the Dictionary of Nomenclature reveals that unique 2-letter combinations for acronyms are nearly exhausted. That is the reason for the change in the rule for new acronyms where at least three characters are now required.
3.5.2 Examples of improper designations
| BD^4°14 | use of ``deg symbol'', declination sign missing |
| N221 | no space, unclear source : NGC or N in LMC ? |
| GRO^J317-85 | leading zero in right ascension missing |
| P^43578 | one letter acronym is ambiguous |
| RC^0401+0456 | missing flag letter J for Julian 2000 equatorial coordinates. |
3.6 Helpful Hints
There are further documents which provide help on:4. Advice on designations
Advice on specific problems may be obtained from the following IAU Working Group Designations representatives:
- Marion Schmitz - Chair
-
IPAC - Caltech
MS 100-22
PASADENA, CA 91125, USA
Phone: +1 626 395 1873 ⋅ Fax: .
Email: mschmitz(at)ipac.caltech.edu - Heinz J. Andernach
-
Depto. de Astronomia, Univ. Guanajuato
Apdo. Postal 144
Guanajuato, C.P. 36000, Mexico
Phone: +52 473 732 9548
or 473 732 9607 ⋅ Fax: +52 473 732 0253
Email: heinz(at)astro.ugto.mx - Kirk Borne
-
George Mason University
Computational and Data Sciences Department, MS 6A2
Fairfax, VA 22030, USA
Phone: +1 703.993.8402 ⋅ Fax: +1 703.993.9300
Email: kborne(at)gmu.edu - Oleg Malkov
-
Centre for Astronomical Data
Institute of Astronomy of the Russian Academy of Sciences
48 Pyatnitskaya St.
109017 Moscow, Russia
Phone: -— ⋅ Fax: -—
Email: malkov(at)inasan.rssi.ru - Marianne Brouty
-
Observatoire astronomique de Strasbourg
11, rue de l'Université
F-67000 Strasbourg, France
Phone: +33 368 852 2403 ⋅ Fax: -—
Email: marianne.brouty(at)astro.unistra.fr
Working Group members: Please send any updated email addresses or changes of institutes to the IAU Secretariat at: iauinfos(at)iap.fr.
5. Further information
For general information, in particular about existing designations, consult the following references :
Lortet, M.-C., Borde, S., Ochsenbein, F. 1994, The Second Reference Dictionary of the Nomenclature of Celestial Objects, A&AS, 107, 193 (1994A&AS..107..193L) and related publications: - The complete paper edition appeared as Publication Spéciale du CDS, 24, Volumes I and II. Observatoire Astronomique de Strasbourg; a postscript version is available from CDS at URL ftp://cdsarc.u-strasbg.fr/pub/dic2
- The ``On-line'' version of the Dictionary is updated regularly and is available on the World-Wide-Web at http://vizier.u-strasbg.fr/viz-bin/Dic; mirror copies can be accessed at http://vizier.nao.ac.jp/viz-bin/Dic or http://vizier.cfa.harvard.edu/viz-bin/Dic
Fernandez, A., Lortet, M.-C., Spite, F. 1983, The first Dictionary of the Nomenclature of Celestial Objects, A&AS, 52, No 4 (1983A&AS...52....1F) Lortet, M.-C., Spite, F. 1986, First Supplement to the First Dictionary of the Nomenclature of Celestial Objects, A&AS, 64, 329 (1986A&AS...64..329L) Dickel, H. R., Lortet M.-C., de Boer, K. S. 1987, Designation and Nomenclature for Diffuse Radiating Sources , A&AS, 68, 75 (1987A&AS...68...75D) Jaschek C. 1989, Data in Astronomy, Cambridge University Press (1989JBAA...99..192V)