TOI-1333Ab is on a well-aligned orbit. An aligned hot Jupiter around an F-type star with a mutually inclined stellar companion

Abstract

Spin-orbit obliquity measurements of hot-Jupiter systems constrain giant planet migration and tidal evolution. In binary systems, combining stellar obliquities with the orbit-orbit angle ($\gamma$) between the planetary and stellar companion orbits provides further insight into the dynamical influence of stellar companions. Here we aim to determine the projected obliquity ($\lambda$) of the hot Jupiter TOI-1333Ab ($P\approx4.72$ d, $M_{\rm p}\approx2.4$ M$_{\rm J}$) and place the system in the context of hot-Jupiter migration and tidal realignment in binary systems. We analysed spectroscopic observations obtained during planetary transit to model the Rossiter-McLaughlin effect and derive the projected obliquity. We combined this measurement with published system parameters and constraints on the wide stellar companion orbit to assess plausible migration scenarios. We measure a projected obliquity of $\lambda=-5 \pm 10^\circ$, showing that TOI-1333Ab is well aligned with the stellar spin axis of its F-type host star. The low obliquity and its modest eccentricity ($e=0.073^{+0.092}_{-0.052}$) are consistent with either disc-driven migration or high-eccentricity migration followed by efficient tidal circularisation and realignment. With an effective temperature of $6274\pm94$ K, the host star lies above the canonical Kraft break where the systems are frequently misaligned. Despite this, we find the system to be well aligned. In comparison with other planetary systems in binaries, TOI-1333 occupies a relatively isolated region in projected obliquity-orbit-orbit angle ($\gamma=81.5\pm1.1^\circ$) space, making it a valuable system for studying the interplay between migration, tides, and stellar companions.