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

TL;DR

This study combines Gaia, Hipparcos, and radial velocity data to precisely constrain orbits of low-mass companions, successfully characterizing the smallest known Jupiter analog and confirming seven low-mass companions.

Contribution

The paper introduces a robust method for orbit determination of low-mass companions using combined astrometric and radial velocity data, including Gaia DR2 and EDR3.

Findings

Characterized orbits of HD 190360 b and HD 16160 C for the first time.

Identified HD 190360 b as the smallest well-characterized Jupiter analog.

Method is robust across different Gaia data releases and data subsets.

Abstract

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.