Tycho-2 TDSC Merge Neighbourhood

Table <code>tycho2tdsc_merge_neighbourhood</code> includes all good neighbours for each matched Tycho2tdscMerge object. A good neighbour for a given Tycho2tdscMerge source is a nearby Gaia object whose position is compatible (within position errors) with the Tycho2tdscMerge target. The cross-match algorithm is not symmetric and searches Tycho2tdscMerge source counterparts in Gaia. The cross-match algorithm is positional and exploits the full 5 parameter covariance matrix of the Gaia astrometric solution when available and the external catalogue positions and position errors. In addition it takes into account the Gaia environment using the local density.
Please note that the cross-match algorithm is a trade-off between multiple requirements, in particular between completeness and correctness. It is thus not limited to a simple cone search.
Reference papers:

Marrese et al. (2017)
Marrese et al. (2019)