Abstract
Astronomical objects may be classified into types in many ways, and the evolution of such categorisations changes with new discoveries and progress in astrophysical understanding. The SIMBAD database contains information on astronomical objects that have been studied in the published literature, including a field that specifies astronomical object types. As a record that is derived entirely from the literature, a given astronomical object in SIMBAD may have multiple object types, and the list of object types must be maintained and updated. The SIMBAD object type list currently contains some 200 types, that are organised into a hierarchy based on astrophysical concepts. The hierarchical structure also includes relations between object types, and this facilitates searches of SIMBAD to obtain lists of all of the astronomical objects in a given category independently of the publisher or the year of publication. We will explain the organisation of astronomical object types in SIMBAD and how they may be used in queries of the SIMBAD database, and visualised on all-sky maps.
Highlights
The SIMBAD database [1] contains a lot of information on astronomical objects
It is fundamental that the CDS team can give the most detailed object type as a main type to the users, which means that we have to rely on a robust algorithm to decide when the main type should be changed and when contradictory classifications should be checked
Objects with the highest priority for the main object type are at the bottom, while objects with the lowest priorities are at the top
Summary
The SIMBAD database [1] contains a lot of information on astronomical objects Among these the object type is of crucial importance. The list of object types in SIMBAD was mostly phenomenological, and organized as a linear hierarchy This list is still the one given to the users on the web site when clicking on ‘Object types.”. The variable stars are not categorized separately anymore as in most cases they correspond to an evolutionary status or/and initial mass (e.g. a RR Lyrae is on the Horizontal Branch, and an Orion variable is an YSO) This new list is still hierarchical, though the hierarchy has changed, but the compatibilities between object types are much more complex than before. Compare two object types according to the levels and branches in the hierarchy tree
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