The designation of subcomponents of a source still presents problems and a satisfactory solution is being sought. In the meantime, several approaches have been tried. These are described below with their advantages and disadvantages. In addition, some suggestions are provided to help you locate the reference and/or the subcomponent (object on the sky).
In practice, the inclusion of the parent source in the designation of the subcomponent is needed when the designation would otherwise be ambiguous, as in the case of IRS 3 which might refer to NGC 7538 IRS 3, to W 3 IRS 3, etc.
Descriptive designations are made of just letters or numbers, relative directions, or combinations thereof, or sickle, eagle, column I, arc, streamer, jet...
W 3 C, W 3 IRS 5, W 3 (OH), DR 21:CO 1, W 49 A, Sgr B2 where the larger (parent) sources are radio sources W 3, DR 21, W 49, and Sgr B
Sgr B2 Main, Sgr B2 North, W 49 A North, W 49 A North:G, W 49 A North:G1 where these examples show the division into additional subcomponents and the (optional) use of : to help delineate the hierarchical nature.
Advantage - within the context of the particular paper which names the components, these descriptive or simple subcomponent designations are quite clear and useful.
Disadvantages - however, the same object may receive a different letter designation by two different authors studying the region at different wavelengths; similarly the same letter may be used to designate different components within the same source. In addition, it is often difficult to find the reference to the subcomponent at a later date.
The advantage of this technique is that later researchers can easily find the reference for ASR 122 by searching for ASR in the Interactive Dictionary of Acronyms.
The disadvantage is that ASR 122 does not convey any information about the nature of the subcomponent (you have to look up the reference).
The methods are very dependent from the database. Some examples are shown.
Within NED subcomponents generally contain the host object as the leading part of the name. The structure is "root_name" ":" "[abdyyyy]" "ID" (all without the quotes). The "root_name" is one of the cross-identifications of the host object, the colon, :, is used as a seperator, the characters within square brackets contains the first letters of the first three authors last names followed by the year of publication, and, finally, the "ID" is the designation given to the object by the authors. The "root_name" is either the name of the host given by the authors or a more consistent name used in NED.
Subcomponents can be found in NED by using the "BY NAME" search option and supplying the host name. This name is "wildcarded" and all objects with the host name as a prefix are retrieved. This wildcarding can also be turned off so the user gets ONLY the host information, if desired.
To search for possible subcomponents of a source (and find the relevant references), one can use the Interactive Dictionary of Acronyms and under "Choose one of the Info possibilities: " select "included in object" and then under "Type in your words" put the name of the object.
If the parent object is essential for locating a source such as IRS sources (W 3 IRS 5, NGC 7538 IRS 5, etc.) then you may find both the parent source and subcomponents listed. If it is not essential, then you will not. For example, for parent object W 3 one finds the following components: