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Description
This section describes the "class" parameter, which is included in many tables in the HEASARC database. It can be used to select objects according to their classifications. Each object is assigned a four digit numeric code to represent its object classification. The first digit describes the global classification (e.g., AGN or star). The following digits assign further classifications or properties such as spectral type, or type of AGN. Each sub-class is chosen to contain a unique set of properties. For example, all normal (non-degenerate) stars have the first digit set to 2. The second digit for stars indicates the spectral type (O, B, etc.), the third digit the numerical sub-type, and the last digit the luminosity class; thus, a G5V star will have the class code of 2555. All stars later (cooler) than F0 have a "class" number between 2400 and 2999. As another example, all AGN have class codes that lie between 7000 and 7999; a search by class for AGN would thus be made by doing a search of the class parameter with the range set from 7000 to 7999. It should be emphasized that the class assignments of the same source found in different databases may not always be identical, and, for any given database, the class codes may not always be present, correct, or complete: see the database help for the particular database in question to determine how the class codes were constructed. ALWAYS USE THE CLASS CODES WITH THESE CAVEATS IN MIND. This is a service provided by NASA HEASARC .
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