The 14 Her Planetary System: Companion Masses and Architecture from Radial Velocities and Astrometry

Abstract

We combine Hubble Space Telescope (HST) Fine Guidance Sensor, Hipparcos, and Gaia DR3 astrometric observations of the K0 V star 14 Her with the results of an analysis of extensive ground-based radial velocity data to determine perturbation orbits and masses for two previously known companions, 14 Her b and c. Radial velocities obtained with the Hobby-Eberly Telescope and from the literature now span over 25 years. With these data we obtain improved radial velocity (RV) orbital elements for both the inner companion, 14 Her b and the long-period outer companion, 14 Her c. We also find evidence of an additional RV signal with P ~ 3789^d. We then model astrometry from Hipparcos, HST, and Gaia with RV results to obtain system parallax and proper motion, perturbation periods, inclinations, and sizes due to 14 Her b and c. We find P _b = 1767.6 ± 0.2 days, perturbation semimajor axis α _b = 1.3 ± 0.1 mas, and inclination i _b = 36° ± 3°, P _c = 52160 ± 1028 days, perturbation semimajor axis α _c = 10.3 ± 0.7 mas, and inclination i _c = 82° ± 14°. In agreement with a past investigation, the 14 Her b, c orbits exhibit significant mutual inclination. Assuming a primary mass M _* = 0.98 ± 0.04M _⊙, we obtain companion masses ${{ \mathcal M }}_{{\rm{b}}}={8.5}_{-0.8}^{+1.0}$ ${{ \mathcal M }}_{\mathrm{Jup}}\,$ and ${{ \mathcal M }}_{{\rm{c}}}={7.1}_{-0.6}^{+1.0}$ ${{ \mathcal M }}_{\mathrm{Jup}}$ .