  To fully constrain the orbits of low mass circumstellar companions, we
conduct combined analyses of the radial velocity data as well as the Gaia and
Hipparcos astrometric data for eight nearby systems. Our study shows that
companion-induced position and proper motion differences between Gaia and
Hipparcos are significant enough to constrain orbits of low mass companions to
a precision comparable with previous combined analyses of direct imaging and
radial velocity data. We find that our method is robust to whether we use Gaia
DR2 or Gaia EDR3, as well as whether we use all of the data, or just proper
motion differences. In particular, we fully characterize the orbits of HD
190360 b and HD 16160 C for the first time. With a mass of 1.8$\pm$0.2$m_{\rm
Jup}$ and an effective temperature of 123-176 K and orbiting around a Sun-like
star, HD 190360 b is the smallest Jupiter-like planet with well-constrained
mass and orbit, belonging to a small sample of fully characterized Jupiter
analogs. It is separated from its primary star by 0.25$''$ and thus may be
suitable for direct imaging by the CGI instrument of the Roman Space Telescope.
