APASS DR9 Join

The table links the external catalogue original sourceId (originalExtSourceId) to the corresponding additional numerical identifier (cleanApassdr9Oid).Both originalExtSourceId and cleanApassdr9Oid are present in the cross-match output tables (Apassdr9BestNeighbour and Apassdr9Neighbourhood). However, in case there are suspected duplicates in the external catalogue, different originalExtSourceId will correspond to the same cleanApassdr9Oid.In the cross-match output table only the originalExtSourceId of the source with the best astrometry among the suspected duplicates will be listed.

In practice, users may use the originalExtSourceId in the original catalogue to find the matching source with the best astrometry. Users interested in all matching suspected duplicates should instead use the cleanApassdr9Oid in the join with the cross-match result tables.See Chapter [chap:crossmatch] for more details on the duplicates in the external catalogues and their treatment in the cross-match computations.