Abstract

In order to study their binary fraction, we searched for companions of Hipparcos catalog stars from the proper motion anomaly (PMa) they induce on their host star. This quantity, defined as the difference between the short-term proper motion vectors measured by Gaia (2014-2017) and the long-term Hipparcos-Gaia proper motion (1991-2016), is a sensitive astrometric tracer of the presence of massive orbiting companions. Thanks to the precision of Gaia and the long Hip-Gaia time baseline, the median accuracy we obtain on the tangential velocity anomaly reaches 26 cm/s per parsec of distance. For nearby stars, this enables us to identify low mass companions, well into the planetary regime. I will present the examples of the detection of several exoplanets previously known from radial velocity (Eps Eri b, Eps Ind Ab, Pi Men b). In addition, we searched the Gaia EDR3 catalog for spatially resolved bound companions of nearby stars within 100pc, based on a common proper motion (CPM) approach. I will present an overview of our results on the PMa and CPM analyses. We obtain a binary fraction of 43% for the Hipparcos catalog stars, including several hundred planetary mass companion candidates. The characterization of these exoplanet candidates using a combination of Gaia data with various observing techniques (imaging, interferometry, transits, radial velocity) appears particularly promising.