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:
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).
Ex:
QSO^004848–4242.8
could have been designated by
QSO^0048–427 or
QSO^0048–42
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.
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).
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.
If the designation requires the use of punctuation or special characters, the
recommendations are the following:
Ex:
DR^21/23 refers to
DR^21 and
DR^23, not
(DR^21,
DR^22,
DR^23)
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.
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.
Advice on specific problems may be obtained from the following IAU Working
Group Designations representatives:
Working Group members: Please send any updated email addresses or changes
of institutes to the IAU Secretariat at:
For general information, in particular about existing designations,
consult the following references :
(J2000.0)
00h51m09.38s –42° 26' 33.8'' = 012.78908 –42.44272
(B1950.0)
00h48m48.97s –42° 42' 52.1'' = 012.20404 –42.7144
3.3 Specifier
3.4 Punctuation and special characters
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
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
MS 100-22
PASADENA, CA 91125, USA
Phone: +1 626 395 1873 ⋅ Fax: .
Email:
Apdo. Postal 144
Guanajuato, C.P. 36000, Mexico
Phone: +52 473 732 9548
Email:
Computational and Data Sciences Department, MS 6A2
Fairfax, VA 22030, USA
Phone: +1 703.993.8402 ⋅ Fax: +1 703.993.9300
Email:
Institute of Astronomy of the Russian Academy of Sciences
48 Pyatnitskaya St.
109017 Moscow, Russia
Phone: -— ⋅ Fax: -—
Email:
11, rue de l'Université
F-67000 Strasbourg, France
Phone: +33 368 852 2403 ⋅ Fax: -—
Email:
5. Further information