TOI-5398 radial velocity curve

From the RM effect modelling, we obtained a sky-projected obliquity of {lambda}=3.0^+6.8^_-4.2_deg for TOI-5398 b, consistent with the planet being aligned. Thanks to the stellar rotation period knowledge, we estimated the true 3D obliquity {psi}=(13.2+/-8.2)deg. Based on theoretical considerations, the orientation we measure is unaffected by tidal effects, offering a direct diagnostic for understanding the planetary system's formation path.

The orbital characteristics of TOI-5398, with its compact architecture, eccentricity consistent with circular orbits, and hints of orbital alignment, appear more compatible with the disc-driven migration scenario. TOI-5398's relative youth (compared with similar compact systems) coupled with an exceptional suitability for transmission spectroscopy studies, presents an outstanding opportunity to establish a benchmark for exploring the disc-driven migration model.