The True Stellar Obliquity of a Sub-Saturn Planet from the Tierras Observatory and the Keck Planet Finder
Creators
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1.
Harvard-Smithsonian Center for Astrophysics
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2.
Massachusetts Institute of Technology
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3.
University of Amsterdam
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4.
California Institute of Technology
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5.
University of California, Berkeley
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6.
NASA Exoplanet Science Institute
Abstract
We measure the true obliquity of TOI-2364, a K dwarf with a sub-Saturn-mass (Mp = 0.18 MJ) 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.
Copyright and License
© 2025. The Author(s). Published by the American Astronomical Society.
Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
Acknowledgement
The Tierras Observatory is supported by the National Science Foundation under Award No. AST-2308043. S.W.Y. and J.G.-M. gratefully acknowledge support from the Heising–Simons Foundation. J.G.-M. acknowledges support from the Pappalardo family through the MIT Pappalardo Fellowship in Physics. This work was supported by a NASA Keck PI Data Award, administered by the NASA Exoplanet Science Institute. Data presented herein were obtained at the W. M. Keck Observatory from telescope time allocated to the National Aeronautics and Space Administration through the agency's scientific partnership with the California Institute of Technology and the University of California. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. Some of the data presented in this paper were obtained from the Mikulski Archive for Space Telescopes (MAST) at the Space Telescope Science Institute. The specific observations analyzed can be accessed via MAST (MAST Team 2021a; MAST Team 2021b).
Facilities
All-Sky Automated Survey for Supernovae, Transiting Exoplanet Survey Satellite, Zwicky Transient Facility, Tierras Observatory, Keck:I (KPF) - .
Software References
TEPCat (J. Southworth 2011), emcee (D. Foreman-Mackey et al. 2013), photutils (L. Bradley et al. 2023), rmfit (G. Stefànsson et al. 2022), radvel (B. J. Fulton et al. 2018), batman (L. Kreidberg 2015), EXOFASTv2 (J. D. Eastman et al. 2019).
Files
Tamburo_2025_AJ_170_34.pdf
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Additional details
Additional titles
- Alternative title
- The True Stellar Obliquity of a Sub-Saturn Planet from the Tierras Observatory and KPF
Related works
- Is new version of
- Discussion Paper: arXiv:2505.03628 (arXiv)
- Is supplemented by
- Dataset: 10.17909/T9-ST5G-3177 (DOI)
- Dataset: 10.17909/T9-NMC8-F686 (DOI)
Funding
- National Science Foundation
- AST-2308043
- Heising-Simons Foundation
- 51 Pegasi b Fellowship -
- Massachusetts Institute of Technology
- MIT Pappalardo Fellowship in Physics. -
- National Aeronautics and Space Administration
- Keck PI Data Award -
- W. M. Keck Foundation
Dates
- Accepted
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2025-05-05
- Available
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2025-06-12Published