Friends of Hot Jupiters II: No Correspondence Between Hot-Jupiter Spin-Orbit Misalignment and the Incidence of Directly Imaged Stellar Companions

TL;DR

This study investigates whether hot Jupiters with misaligned or eccentric orbits are more likely to have stellar companions, finding no significant correlation despite a high overall companion fraction.

Contribution

It provides the first direct imaging survey comparing stellar companion incidence between misaligned/eccentric and aligned hot Jupiters, revealing no correlation.

Findings

Stellar companion fraction around hot Jupiters is approximately 50%.

No link found between orbit misalignment and presence of stellar companions.

About 72% of hot Jupiters are in multi-planet or multi-star systems.

Abstract

Multi-star systems are common, yet little is known about a stellar companion's influence on the formation and evolution of planetary systems. For instance, stellar companions may have facilitated the inward migration of hot Jupiters towards to their present day positions. Many observed short period gas giant planets also have orbits that are misaligned with respect to their star's spin axis, which has also been attributed to the presence of a massive outer companion on a non-coplanar orbit. We present the results of a multi-band direct imaging survey using Keck NIRC2 to measure the fraction of short period gas giant planets found in multi-star systems. Over three years, we completed a survey of 50 targets ("Friends of Hot Jupiters") with 27 targets showing some signature of multi-body interaction (misaligned or eccentric orbits) and 23 targets in a control sample (well-aligned and circular orbits). We report the masses, projected separations, and confirmed common proper motion for the 19 stellar companions found around 17 stars. Correcting for survey incompleteness, we report companion fractions of $48\%\pm9\%$, $47\%\pm12\%$, and $51\%\pm13\%$ in our total, misaligned/eccentric, and control samples, respectively. This total stellar companion fraction is $2.8\,\sigma$ larger than the fraction of field stars with companions approximately $50-2000\,$AU. We observe no correlation between misaligned/eccentric hot Jupiter systems and the incidence of stellar companions. Combining this result with our previous radial velocity survey, we determine that $72\% \pm 16\%$ of hot Jupiters are part of multi-planet and/or multi-star systems.