English

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

Earth and Planetary Astrophysics 2025-10-24 v1

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 Teff=6320±120T_{\rm eff}=6320\pm120 K, using WIYN/NEID. We confirm its near-polar architecture, measuring a sky-projected obliquity of λ=68.15.3+7.5\lambda=-68.1^{+7.5}_{-5.3} degrees and a true obliquity of ψ=72.26.6+6.4\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 5.2σ5.2\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 65\sim 65 degrees, supporting predictions from secular resonance crossing for sub-Saturns around rapidly rotating hot stars.

Keywords

Cite

@article{arxiv.2510.20740,
  title  = {Early Evidence for Polar Orbits of Sub-Saturns Around Hot Stars},
  author = {Emma Dugan and Xian-Yu Wang and Agustin Heron and Hareesh Gautham Bhaskar and Malena Rice and Cristobal Petrovich and Songhu Wang},
  journal= {arXiv preprint arXiv:2510.20740},
  year   = {2025}
}

Comments

16 pages, 3 figures, accepted for publication in ApJL