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Description
The multiplicity fraction of stars, down to the substellar regime, is a parameter of fundamental importance for stellar formation, evolution, and planetology. The census of multiple stars in the solar neighborhood is however incomplete. The presence of a companion in orbit around a star affects its proper motion. We aim at detecting companions of Hipparcos catalog stars from the proper motion anomaly (PMa) they induce on their host star, that is, the difference between their long-term Hipparcos-Gaia and short-term Gaia proper motion vectors. We also aim at detecting resolved, gravitationally bound companions of the Hipparcos catalog stars (117955 stars), and of the Gaia EDR3 stars closer than 100 c (542232 stars). Using the Hipparcos and EDR3 data, we revise the PMa catalog for the Hipparcos stars. To identify gravitationally bound visual companions of our sample, we search the Gaia EDR3 catalog for common proper motion (CPM) candidates. The detection of tangential velocity anomalies with a median accuracy of 26cm/s per parsec of distance is demonstrated with the EDR3. This improvement by a factor 2.5 in accuracy compared to the Gaia DR2 results in PMa detection limits on companions well into the planetary mass regime for many targets. We identify 37515 Hipparcos stars presenting a PMa at significant level (S/N>3), that is, a fraction of 32% (compared to 30% for the DR2) and 12914 (11%) hosting CPM bound candidate companions. Including the Gaia EDR3 RUWE>1.4 as an additional indicator, 50,720 stars of the Hipparcos catalog (43%) exhibit at least one signal of binarity. Among the Gaia EDR3 stars located within 100 pc, we find CPM bound candidate companions for 39,490 stars (7.3% of the sample). The search for companions using a combination of the PMa, CPM and RUWE indicators significantly improves the exhaustivity of the multiplicity survey. The detection of CPM companions of very bright stars (heavily saturated on the Gaia detectors) that are classical benchmark objects for stellar physics provides a useful proxy to estimate their distance with a higher accuracy than Hipparcos.
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