A Testbed for Tidal Migration: the 3D Architecture of an Eccentric Hot Jupiter HD 118203 b Accompanied by a Possibly Aligned Outer Giant Planet

Characterizing outer companions to hot Jupiters plays a crucial role in deciphering their origins. We present the discovery of a long-period giant planet, HD 118203 c ($m_{c}=9.2^{+4.8}_{-2.7}\ \mathrm{M_{J}}$, $a_{c}=5.54^{+0.14}_{-0.19}$ AU, $e_{c}=0.32^{+0.15}_{-0.14}$) exterior to previously known close-in eccentric hot Jupiter HD 118203 b ($P_{b}=6.135\ \mathrm{days}$, $m_{b}=2.14\pm{0.12}\ \mathrm{M_{J}}$, $r_{b}=1.14\pm{0.029}\ \mathrm{R_{J}}$, $e_{b}=0.31\pm{0.007}$) based on twenty-year radial velocity observations from ELODIE and Keck/HIRES. Using subsequent Rossiter-McLaughlin observations from the Keck Planet Finder (KPF), we measured a low sky-projected obliquity $\lambda_{b}=-11^{\circ}.7^{+7.6}_{-10}$ for HD 118203 b and detected stellar oscillations in the host star, confirming its evolved status. Combining this with the stellar inclination measurement, we constrained the true obliquity of HD 118203 b as $\Psi_{b}<33^{\circ}.5\ (95\%)$, indicating the hot Jupiter is nearly aligned to the host star. Furthermore, by combining radial velocities and Hipparcos-Gaia astrometric acceleration, we constrained the line-of-sight mutual inclination between the hot Jupiter and the outer planet to be $16^{\circ}.7^{+14.6}_{-10.9}$. We also constrained the line-of-sight stellar obliquity for HD 118203 c to be  $17^{\circ}.8^{+18.6}_{-12.4}$. HD 118203 is the first hot Jupiter system where both the true obliquity of the hot Jupiter and the mutual inclination between inner and outer planets have been determined. Our results are consistent with a system-wide alignment, with low mutual inclinations between the outer giant planet, the inner hot Jupiter, and the host star. This alignment, along with the moderate eccentricity of HD 118203 c, implies that the system may have undergone coplanar high-eccentricity tidal migration.