# What is the overlap between the Gaia and the Hipparcos catalog?

Is there any kind of concordance available between the sources in the Hipparcos catalog and the Gaia DR2 catalog? I.e., mapping the Gaia DR2 source_id to the Hipparcos HIP number?

• Do you want the mapping for an individual or small list of objects or for the whole Hipparcos catalog? SIMBAD will do the former e.g. for HD209458 and look under 'Identifiers' – astrosnapper Feb 14 '20 at 15:05
• This is probably unhelpful but the files in cdn.gea.esac.esa.int/Gaia/gdr1/tgas_source/csv (and files in similar directories) do this for GAIA DR1. Unfortunately, there is no corresponding directory for GAIA DR2: cdn.gea.esac.esa.int/Gaia/gdr2 – user21 Feb 17 '20 at 15:58

As part of the Gaia DR2, cross-matches to several catalogues including HIP2 were included. The main reference for this is Marrese et al. (2018) "Gaia Data Release 2. Cross-match with external catalogues: algorithms and results". The resultant matches are included in the tables gaiadr2.hipparcos2_best_neighbour and gaiadr2.hipparcos2_neighbourhood available via the query facilities in the Gaia Archive.