7.3 Alternative astrometric orbit processing

Author(s): Alessandro Sozzetti, Berry Holl, Johannes Sahlmann

This section describes the solutions produced by the development unit responsible for fitting Keplerian parameters to astrometric epoch data of low signal-to-noise ratio (SNR) orbits, like the ones corresponding to planetary-mass or brown-dwarf companions as well as near-equal mass binaries: for spatially-unresolved binaries, the astrometry reflects the motion of the combined photocentre, which for near-equal magnitude binaries is much smaller than the actual astrometric motion of each individual component around their barycentre. This pipeline channel processed 2 457 530 sources that were not sufficiently well modelled in terms of acceleration or binary orbital fits of the non-single stars pipeline (Section 7.2) and ended up with a (non-published) so-called ‘stochastic’ solution. For 629 sources in this stochastic solution sample an orbital fit was produced and is published in the nss_two_body_orbit table with nss_solution_type, OrbitalAlternative (619) and OrbitalAlternativeValidated (10).

For Gaia DR3 an independent, targeted search for significant astrometric orbital signals was performed for a set of almost 20 000 sources, which included host stars with known exoplanet, brown-dwarf, and stellar companions. The composition of the targeted search sample is described in Holl et al. (2023b). The 533 sources identified in this search are found in the nss_two_body_orbit table with nss_solution_type OrbitalTargetedSearch (345) and OrbitalTargetedSearchValidated (188).

The distinction between solution types with and without the suffix “Validated” is explained in Section 7.3.5. Additional details can be found in found in Holl et al. (2023b).