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

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 $T_{\mathrm{eff}}=6320\pm 120$ K, using WIYN/NEID. We confirm its near-polar architecture, measuring a sky-projected obliquity of $\lambda =-68.1_{-5.3}^{+7.5}$ degrees and a true obliquity of $\psi =72.2_{-6.6}^{+6.4}$ 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.

16 pages, 3 figures, accepted for publication in ApJL