Convenience table to be used to join SDSS DR13 catalogue with the cross-match results. The table links the external catalogue original source_id (original_ext_source_id) to the corresponding additional numerical identifier (clean_sdssdr13_oid).
Both original_ext_source_id and clean_sdssdr13_oid are present in the cross-match output tables (sdssdr13_best_neighbour and sdssdr13_neighbourhood).
However, in case there are suspected duplicates in the external catalogue, different original_ext_source_id will correspond to the same clean_sdssdr13_oid. In the cross-match output table only the original_ext_source_id of the source with the best astrometry among the suspected duplicates will be listed.
In practice, users may use the original_ext_source_id in the original catalogue to find the matching source with the best astrometry. Users interested to find all matching suspected duplicates should instead use the clean_sdssdr13_oid in the join with the cross-match result tables.
See Chapter 9 for more details on the duplicates in the external catalogues and their treatment in the cross-match computations.
The unique source identifier in the original external catalogue.
The additional numeric source identifier of the external catalogue, increasing with Declination.