The OATMEAL Survey. II. The 3D Spin–Orbit Obliquity of an Eccentric Transiting Brown Dwarf in the Ruprecht 147 Open Cluster
Creators
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1.
University of Hawaii at Manoa
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2.
California Institute of Technology
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3.
Michigan State University
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Harvard-Smithsonian Center for Astrophysics
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Indiana University Bloomington
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University of California, Santa Cruz
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7.
Massachusetts Institute of Technology
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8.
NASA Exoplanet Science Institute
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9.
University of California, Berkeley
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10.
Jet Propulsion Lab
- 11. Astrophysics & Space Institute, Schmidt Sciences, New York, NY 10011, USA
Abstract
We present a new analysis of the CWW 89 system as part of the Orbital Architectures of Transiting Massive Exoplanets And Low-mass stars (OATMEAL) survey. The CWW 89 system is a member of the 2.8 Gyr old Ruprecht 147 (NGC 6774) cluster and consists of two stars, CWW 89A (EPIC 219388192) and CWW 89B, with the primary hosting a transiting brown dwarf, CWW 89Ab. We use in-transit, highly precise radial velocity measurements with the Keck Planet Finder to characterize the Rossiter–McLaughlin (RM) effect and measure the projected spin–orbit obliquity ∣ λ ∣ = 1.°4 ± 2.°5 and the full 3D spin–orbit obliquity of the brown dwarf to be ψ = 15.1_(−10.9)^(+15.0∘). This value of λ implies that the brown dwarf's orbit is prograde and well-aligned with the equator of the host star, continuing the trend of transiting brown dwarfs showing a preference for spin–orbit alignment ( λ ≈ 0°) regardless of the stellar effective temperature. This contrast with the transiting giant planet population, whose spin–orbit alignments depend on host T eff , shows an increasingly clear distinction in the formation and orbital migration mechanisms between transiting giant planets and transiting brown dwarfs like CWW 89Ab. For this system in particular, we find it plausible that the brown dwarf may have undergone coplanar high-eccentricity migration influenced by CWW 89B.
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 authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the Native Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.
Some of the data presented herein were obtained at Keck Observatory, which is a private 501(c)3 nonprofit organization operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.
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.
This research has made use of the NASA Exoplanet Archive, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program.
The research was carried out, in part, at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004) and funded through the President’s and Director’s Research & Development Fund Program.
T.W.C. is supported by an NSF MPS-Ascend Postdoctoral Fellowship under award 2316566. D.H. acknowledges support from the Alfred P. Sloan Foundation and the National Aeronautics and Space Administration (80NSSC22K0781).
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Additional details
Related works
- Is new version of
- Discussion Paper: arXiv:2506.18971 (arXiv)
Funding
- W. M. Keck Foundation
- Jet Propulsion Laboratory
- California Institute of Technology
- National Aeronautics and Space Administration
- 80NM0018D0004
- National Science Foundation
- 2316566
- Alfred P. Sloan Foundation
- National Aeronautics and Space Administration
- 80NSSC22K0781
Dates
- Submitted
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2025-06-19
- Accepted
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2025-10-29
- Available
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2025-12-04Published online