The PFS view of TOI-677 b: A spin-orbit aligned warm Jupiter in a dynamically hot system

TOI-677 b is part of an emerging class of ``tidally-detached'' gas giants (a/R_ 11) that exhibit large orbital eccentricities and yet low stellar obliquities. Such sources pose a challenge for models of giant planet formation, which must account for the excitation of high eccentricities without large changes in the orbital inclination. In this work, we present a new Rossiter-McLaughlin (RM) measurement for the tidally-detached warm Jupiter TOI-677 b, obtained using high-precision radial velocity observations from the PFS/Magellan spectrograph. Combined with previously published observations from the ESPRESSO/VLT spectrograph, we derive one of the most precisely constrained sky-projected spin-orbit angle measurements to date for an exoplanet. The combined fit offers a refined set of self-consistent parameters, including a low sky-projected stellar obliquity of =3. 2^+1. 6-₁. ₅ deg and a moderately high eccentricity of e=0. 460^+0. 019-₀. ₀₁₈, that further constrains the puzzling architecture of this system. We examine several potential scenarios that may have produced the current TOI-677 orbital configuration, ultimately concluding that TOI-677 b most likely had its eccentricity excited through disk-planet interactions. This system adds to a growing population of aligned warm Jupiters on eccentric orbits around hot (T ₄₅₅>6100 K) stars.