RAVE DR5 table lists each matched external catalogue object with its best
neighbour in Gaia.
source_id : Unique Gaia source identifier (long)
A unique single numerical identifier of the source obtained from gaia_source (for a detailed description see gaia_source.source_id)
original_ext_source_id : Original External Catalogue source identifier (string)
The unique source identifier in the original External catalogue.
angular_distance : Angular Distance between the two sources (double, Angle[arcsec])
Angular distance between a Gaia source and its best neighbour in the External Catalogue
gaia_astrometric_params : Number of Gaia astrometric params used (short)
This field indicates the number of Gaia astrometric parameters which were available in Gaia.
The field is set to 2 when only RA and DEC where available, while is set to 5 when RA, DEC,
PMRA, PMDEC and PARALLAX are available and thus used to propagate a Gaia source position to the External Catalogue source coordinates epoch.