Dictionary of Nomenclature of Celestial Objects

We had to accept the challenge of construction of a satisfactory scheme in the course of development of the BDB, Binary star DataBase (http://bdb.inasan.ru, Malkov et al. 2013, Kaygorodov et al. 2012). BDB is constructed as a source combining comprehensive information on binary stars of all observational and evolutionary types. It provides the user with synthesis of data from a large variety of catalogues and databases of binaries of different types: visual, orbital, astrometric, interferometric, eclipsing, spectroscopic, X-ray, etc. The BDB contains all data from catalogues on more than 100,000 stellar systems of multiplicity 2 and more: positional, photometric, spectroscopic, orbital and astrophysical parameters are provided when available. Organization of the information is based on careful cross-identification of the objects.

Based on these categories of objects, we have developed and now use a new consistent scheme of designations of binary/multiple stars. The "BSDB" (Binary Star DataBase) abbreviation is used as the acronym (as we have checked with the Dictionary of Nomenclature of Celestial Objects, the "BDB" acronym is not available for registration). To form the designation, we take equatorial coordinates for the standard equinox of J2000.0 from the catalogues. Coordinates given in the catalogues are precise enough to specify them in the form of HHMMSS.ss+DDMMSS.s or HHMMSS.ss-DDMMSS.s. Then we add a specifier to distinguish systems, pairs, and components (s, p, and c, respectively). Finally, we indicate what component or pair is referred to using numerals and capital letters.

It should be noted that the authors of WDS catalogue (Mason et al. 2001, http://ad.usno.navy.mil/wds/) include in the catalogue results of searches for substellar companions to nearby stars by high-contrast and high-angular-resolution imaging (e.g., Chauvin et al. 2010, 41 objects in the WDS 13447-6348 = TYC 9012-1005-1 system; Janson et al. 2011, 105 objects in the WDS 19062-0453 = lambda Aql system). At least some of the objects are background stars; however, they are also included in WDS and, consequently, in BDB. Another example of a high-multiplicity system in WDS is WDS 05387-6906 = 30 Dor = Tarantula Nebula. Digital speckle interferometry yields some 65 objects in this HII region in the LMC (Weigelt and Baier 1985). The usual capital-letter component designations (e.g., AB, AC, etc.) are insufficient to accommodate the very large number of companions in such systems, so upper/lower case combinations (A,Ca; A,Cb; etc.) were utilized in WDS. The lower-case letters here are not meant to indicate any sort of hierarchical structure within the system.

Currently, 11 WDS systems have 30 or more components and, obviously, this number will increase. That is why we have decided to use numerals to identify components on the upper level of hierarchy. For other levels, we use capital letters A, B, etc.

So, an example of the designation for some triple system would be as follows:
J000144.48+590527.1:s
J000144.48+590527.1:p1A-1B
J000144.48+590527.1:c1A
J000144.48+590527.1:c1B
J000144.48+590527.1:p1-2
J000144.48+590527.1:c2

Note that there is no component "1" in the list. The cause is that "1" is not a star in this system but a pair of stars (1A-1B) and, respectively, it is described with parameters typical for a pair (say, orbital period) and not for a component. The coordinate part of a designation does not vary within the system (in spite of the fact that the components "1" and "2" can differ in coordinates).

Indicating a component designation, we in general follow the WDS notation, but we substitute capital letters for digits (for the upper level of system hierarchy) and small letters and digits for capital letters (for other levels). Thus, we introduce BSDB J043306.62+240954.9:p1BA-1BB for the pair WDS 04331+2410 Ab1,2. The proposed system is extended to other types of binaries. Note that our principal source of photometric (eclipsing) binaries, GCVS Samus et al. 2013, http://www.sai.msu.ru/groups/cluster/gcvs/), has the same coordinate precision as WDS and CCDM (Dommanget and Nys 2002), and the principal catalogue of spectroscopic binaries, SB9, is even more precise (here coordinates should be truncated — not rounded — to form a designation). A newly discovered distant component will be designated by the next vacant digit. The solution of a component in two sub-components will lead to an appearance of two new designations for the subcomponents, with letters A and B in two subsequent positions (e.g., subcomponents 2A and 2B will appear when the component 2 is resolved). In the latter case, the resolved component designation (BSDB Jxxxxxx.xx+xxxxxx.x:c2) will be moved to the "outdated BSDB name" column, and a new designation for the pair (BSDB Jxxxxxx.xx+xxxxxx.x:p2A-2B) will be constructed.

To provide BSDB numbers for all binary systems included in the BDB, we are working to appoint BSDB identifiers to binary and multiple stars of every observational type. For this purpose, we are compiling the general catalog of identifications of binaries, preliminarily named Identification List of Binaries, ILB. The ILB should include BSDB identifications for all binary systems included in the catalogs up to date, as well as leave such possibility open for the coming binary lists/catalogs/surveys.

The most representative catalogues of binary systems (from wide to close pairs) are gradually connected to the ILB. If an object is encountered for the first time, a unique BSDB identifier is attributed to it. Objects that already exist in the previously investigated catalogues are appended to the corresponding ILB entries. New objects (pairs, components) included in stellar systems already existing in ILB lead to adjustments of the relevant sections of the catalog. ILB provides cross-identification with the following widely-used and/or binary identifiers: Name/Bayer/Flamsteed, HD, HIP, GCVS, DM (BD, CD, CPD), CCDM, WDS, ADS, IDS, SBC9, IGR, PSR. Cross-ID problems are solved at this stage, and to do it properly, all available information (positional, photometric and sometimes already contained in catalogues cross-identification) is taken into account.

We believe that the principles underlaying BSDB identifier compilation do satisfy the "IAU Specifications concerning designations for astronomical radiation sources outside the solar system" (unlike, say, similarly coordinate-based WDS and CCDM names). Also, one can easily make sure that the problems typical for binary/multiple-star designation schemes are basically avoided by the BSDB.

Kovaleva D., Malkov O., Kaygorodov P., Karchevskij A., Samus N. "BSDB: a new consistent designation scheme for identifying objects in binary and multiple stars" 2015, Baltic Astronomy, accepted
Kovaleva D.A., Debray B., Kaygorodov P.V., Malkov O.Yu., Oblak E. "VO-accessible Binary star DataBase BDB" 2015, Astronomy and Computing, submitted