Early Evidence for Polar Orbits of Sub-Saturns Around Hot Stars

TL;DR

This study provides evidence that sub-Saturn exoplanets orbiting hot stars tend to have near-polar orbits, supporting theories of their dynamical history and extending previous findings from cool star systems.

Contribution

First measurement of obliquity for a hot-star sub-Saturn, confirming near-polar orbit and suggesting the polar preference extends above the Kraft break.

Findings

Sub-Saturns around hot stars are often near-polar.

The polar orbit preference may extend above the Kraft break.

Obliquities near 65 degrees support secular resonance crossing predictions.

Abstract

Sub-Saturns have been reported to preferentially occupy near-polar orbits, but this conclusion has so far been based primarily on systems with cool host stars; obliquity measurements for sub-Saturns orbiting hot stars remain scarce. Expanding the census into the hot-star regime is essential to test whether the polar preference persists across the Kraft break and to diagnose the underlying excitation mechanisms. In this work, we present Rossiter-McLaughlin observations of TOI-1135 b, a sub-Saturn orbiting a hot star with $T_{\rm eff}=6320\pm120$ K, using WIYN/NEID. We confirm its near-polar architecture, measuring a sky-projected obliquity of $\lambda=-68.1^{+7.5}_{-5.3}$ degrees and a true obliquity of $\psi=72.2^{+6.4}_{-6.6}$ degrees. Coupling our new measurement with stellar-obliquity data from the literature, we find that sub-Saturns and hot Jupiters around cool stars are unlikely to be drawn from the same parent distribution at the $5.2\sigma$ level, consistent with weaker tidal realignment induced by lower-mass planets. Of the two known misaligned sub-Saturns around hot stars, both are near-polar, suggesting that the polar preference may extend above the Kraft break. Moreover, their obliquities lie near $\sim 65$ degrees, supporting predictions from secular resonance crossing for sub-Saturns around rapidly rotating hot stars.