Stellar companions sculpt hot Jupiter formation and spin-orbit evolution

Abstract: Stellar companions can drive hot-Jupiter (HJ) migration and spin-orbit misalignment, but their role in HJ formation remains uncertain. We construct a homogeneous census of resolved stellar companions to $147$ northern HJs with measured projected obliquities. We obtain uniform adaptive-optics imaging and combine these observations with {\it Gaia} common proper-motion pairs to identify 8 new companion candidates, bringing the \textit{observed} companion fraction to $71/147=48\%$. Modeling the full survey selection function yields an \textit{intrinsic} companion fraction of $62\pm5\%$ for mass ratios $q_\star=0.1$-$1$ and projected separations $s=50$-$50{,}000$~au, roughly 3-4$\times$ enhanced relative to field stars. Including white-dwarf companions would increase this fraction further. HJs with resolved companions at $50$-$2{,}000$~au are nearly twice as likely to be misaligned compared to systems without detected companions: $46\%$ compared to $24\%$ ($p=0.009$). The misaligned fraction rises steadily from $5\%$ among the coolest hosts to $80\%$ among the hottest, without a sharp transition at the Kraft Break, while the intrinsic companion fraction remains roughly constant across the temperature range. These trends are consistent with HJs beginning with a broad obliquity distribution, followed by progressively weaker tidal realignment at higher stellar temperatures. Contrary to previous work, we find that most stellar companions in our sample are capable of driving eccentric Kozai-Lidov (EKL) oscillations to the tidal limit under suitable orbital configurations, making high-eccentricity migration dynamically promising. Taken together, these results indicate that stellar companions sculpt HJ formation and spin--orbit architectures.