Companion–Obliquity Associations Beyond Hot Jupiters

Determine whether stellar companions are associated with spin–orbit misalignment among warm Jupiters and sub-Saturns, using homogeneous companion censuses corrected for observational selection effects.

Background

Warm Jupiters and sub-Saturns provide complementary tests of migration and tidal evolution because their lower tidal realignment efficiency may preserve more of their formation-related obliquity. Existing studies report differing obliquity distributions for systems with and without known companions, but the companion classifications are heterogeneous and generally do not account for incompleteness.

The paper establishes a companion–obliquity association for hot Jupiters, but whether the same relationship applies to warm Jupiters and sub-Saturns remains unresolved. A comparable, selection-corrected companion census for those populations is needed.

References

Whether stellar companions are similarly associated with misalignment among warm Jupiters and sub-Saturns remains unknown. Existing studies distinguish systems with and without known companions, but do not correct for the selection function. Moreover, planets in known binaries include both aligned and misaligned examples \citep{WuMurray2003,Hjorth2021,Gupta2024,Veldhuis2026}, so individual systems do not establish a population-wide association. Our HJ census does reveal such an association between obliquity and companions (Figure \ref{fig:misalignment_single_panel}). A comparable companion census of warm Jupiters and sub-Saturns is needed to determine whether this result extends beyond HJs.

— Stellar companions sculpt hot Jupiter formation and spin-orbit evolution  (2609.19249 - Shariat et al., 16 Sep 2026) in Section 5.8, final paragraph