rare designator prefixes

These are prefixes used in designators of objects (e.g., stars or galaxies) that are not commonly seen for any large number of objects. An IAU initiative offers formalized designation formats with the aim of object-references that are and remain unique and traceable, but designator prefixes actually used for objects are ultimately chosen by those who write or talk about the objects, and they often choose something convenient to write and say, often shortening the prefix. Such designator prefixes in use include:

• prefixes from old catalogs, kept in circulation through continued interest in one or a few objects. It might be a designator specific to the catalog, or it might be, or include, an indicator of the discoverer.
• such prefixes when research interest in some object in such an old catalog has been revived, such as when an extra-solar planet is discovered around a star which has\ long been rather ordinary as far as research is concerned.
• prefixes coined in a more recent paper based on the object's discoverer.
• prefixes reflecting any of the many compiled lists of objects in papers, which range from thousands down to tens or fewer, too short to call a "catalog". The prefix may have been coined by the compiler of the list, or by a subsequent researcher who is referencing an object in the list.

See also double star designation.