Optimized modeling of Gaia-Hipparcos astrometry for the detection of the smallest cold Jupiter and confirmation of seven low mass companions

To fully constrain the orbits of low mass circumstellar companions, we conduct combinedanalyses of the radial velocity data as well as the Gaia and Hipparcos astrometric data foreight nearby systems. Our study shows that companion-induced position and proper motiondifferences between Gaia and Hipparcos are significant enough to constrain orbits of low masscompanions to a precision comparable with previous combined analyses of direct imagingand radial velocity data. We find that our method is robust to whether we use Gaia DR2 orGaia EDR3, as well as whether we use all of the data, or just proper motion differences. Inparticular, we fully characterize the orbits of HD 190360 b and HD 16160 C for the first time.With a mass of 1.80.2 𝑀Jup and an effective temperature of 123-176K and orbiting around aSun-like star, HD 190360 b is the smallest Jupiter-like planet with well-constrained mass andorbit, belonging to a small sample of fully characterized Jupiter analogs. It is separated fromits primary star by 0.2500 and thus may be suitable for direct imaging by the CGI instrumentof the Roman Space Telescope.