An Obliquity Measurement of the Hot Neptune TOI-1694b
Creators
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1.
California Institute of Technology
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2.
Flatiron Institute
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3.
University of Hawaii at Manoa
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4.
University of California, Los Angeles
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5.
University of California, Berkeley
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6.
NASA Exoplanet Science Institute
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7.
Massachusetts Institute of Technology
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8.
Jet Propulsion Lab
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9.
Schmidt Sciences
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10.
W.M. Keck Observatory
Abstract
We present spectral observations of the multiplanet host TOI-1694 during the transit of TOI-1694b, a 26.1 M⊕ hot Neptune with a 3.77 day orbit. By analyzing radial velocities obtained from the Keck Planet Finder, we modeled the Rossiter–McLaughlin effect and constrained the sky-projected obliquity to 9°_(−18°)_^(+22°) which is strong evidence for a nearly aligned orbit. TOI-1694b is one of fewer than 10 small planets accompanied by confirmed outer giant planets for which the obliquity has been measured. We consider the significance of the outer planet TOI-1694c, a Jupiter-mass planet with a 1 yr orbit, and its potential role in influencing the orbit of TOI-1694b to its current state. Incorporating our measurement, we discuss the bifurcation in hot Neptune obliquities and present evidence for an independent polar population. The observed polar planets nearly ubiquitously have periods of ≤6 days and mass ratios of 10−4. Early perturbations by outer companions from resonance crossings in the disk-dispersal stage provide the most compelling explanation for this population. Systems which lack the necessary configuration will retain their primordial obliquity, since hot Neptunes lack the angular momentum needed to realign their hosts on relevant timescales.
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
We are grateful to Luke Bouma for valuable conversations about TESS photometry, and to Konstantin Batygin for a review of our dynamical arguments. A.W.H. acknowledges funding support from NASA grant No. 80NSSC24K0161. This research was carried out, in part, at the Jet Propulsion Laboratory and the California Institute of Technology under a contract with the National Aeronautics and Space Administration and funded through the President’s and Director’s Research & Development Fund Program.
The authors acknowledge the use of public TESS data from pipelines at the TESS Science Office and at the TESS SPOC at NASA Ames Research Center. This research has made use of the NASA Exoplanet Archive and Exoplanet Follow-up Observation Program website, which are operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program.
Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. We 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.
Facilities
TESS - , Keck:I - KECK I Telescope (KPF).
Software References
astropy (Astropy Collaboration et al. 2022), batman (L. Kreidberg 2015), emcee (D. Foreman-Mackey et al. 2013), lightkurve (Lightkurve Collaboration et al. 2018), matplotlib (J. D. Hunter 2007), numpy (C. R. Harris et al. 2020), pandas (pandas development team 2020), scipy (P. Virtanen et al. 2020), spinspotter (R. J. Holcomb et al. 2022), tesscut (C. E. Brasseur et al. 2019), unpopular (S. Hattori et al. 2022).
Files
Handley_2025_AJ_169_212.pdf
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Additional details
Related works
- Is new version of
- Discussion Paper: arXiv:2412.07950 (arXiv)
Funding
- National Aeronautics and Space Administration
- 80NSSC24K0161
- Jet Propulsion Laboratory
Dates
- Accepted
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2025-02-14
- Available
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2025-03-18Published online