The True Stellar Obliquity of a Sub-Saturn Planet from the Tierras Observatory and the Keck Planet Finder

July 2025 • 2025AJ....170...34T

Authors • Tamburo, Patrick • Yee, Samuel W. • García-Mejía, Juliana • Stefánsson, Gudmundur • Charbonneau, David • Bieryla, Allyson • Howard, Andrew W. • Isaacson, Howard • Fulton, Benjamin J. • Householder, Aaron

Abstract • We measure the true obliquity of TOI-2364, a K dwarf with a sub-Saturn-mass (M_p = 0.18 M_J) transiting planet on the upper edge of the hot-Neptune desert. We used new Rossiter–McLaughlin observations gathered with the Keck Planet Finder to measure the sky-projected obliquity λ = 7° + 10°–11°. Combined with a stellar rotation period of 23.47 ± 0.29 days measured with photometry from the Tierras Observatory, this yields a stellar inclination of 90° ± 13° and a true obliquity ψ = 15 .° 6 + 7 .° 7–7 .° 3, indicating that the planet's orbit is well aligned with the rotation axis of its host star. The determination of ψ is important for investigating a potential bimodality in the orbits of short-period sub-Saturns around cool stars, which tend to be either aligned with or perpendicular to their host stars' spin axes.

Links

• PDF https://iopscience.iop.org/article/10.3847/1538-3881/add530/pdf
• PREPRINT http://arxiv.org/abs/2505.03628
• ELECTR https://doi.org/10.3847/1538-3881/add530