TESS Giants Transiting Giants. VI. Newly Discovered Hot Jupiters Provide Evidence for Efficient Obliquity Damping after the Main Sequence

Creators: Saunders, Nicholas¹; Grunblatt, Samuel K.²; Chontos, Ashley³; Dai, Fei¹; Huber, Daniel¹; Zhang 张, Jingwen 婧雯¹; Stefánsson, Guđmundur⁴; van Saders, Jennifer L.¹; Winn, Joshua N.³; Hey, Daniel¹; Howard, Andrew W.⁵; Fulton, Benjamin⁶; Isaacson, Howard^{7, 8}; Beard, Corey⁹; Giacalone, Steven⁵; Van Zandt, Judah¹⁰; Murphey, Joseph M. Akana¹¹; Rice, Malena¹²; Blunt, Sarah^{5, 13}; Turtelboom, Emma⁷; Dalba, Paul A.¹¹; Lubin, Jack⁹; Brinkman, Casey¹; Louden, Emma M.¹²; Page, Emma¹⁴; Watkins, Cristilyn N.¹⁵; Collins, Karen A.¹⁵; Stockdale, Chris¹⁶; Tan, Thiam-Guan¹⁷; Schwarz, Richard P.¹⁵; Massey, Bob¹⁸; Howell, Steve B.¹⁹; Vanderburg, Andrew²⁰; Ricker, George R.²⁰; Jenkins, Jon M.¹⁹; Seager, Sara²⁰; Christiansen, Jessie L.^{6, 21}; Daylan, Tansu²²; Falk, Ben²³; Brodheim, Max²⁴; Gibson, Steven R.⁵; Hill, Grant M.²⁴; Holden, Bradford¹¹; Householder, Aaron²⁰; Kaye, Stephen⁵; Laher, Russ R.⁶; Lanclos, Kyle²⁴; Petigura, Erik A.¹⁰; Roy, Arpita²⁵; Rubenzahl, Ryan A.⁵; Schwab, Christian²⁶; Shaum, Abby P.⁵; Sirk, Martin M.⁷; Smith, Christopher L.⁷; Walawender, Josh²⁴; Yeh, Sherry²⁴

1. University of Hawaii at Manoa
2. Johns Hopkins University
3. Princeton University
4. University of Amsterdam
5. California Institute of Technology
6. NASA Exoplanet Science Institute
7. University of California, Berkeley
8. University of Southern Queensland
9. University of California, Irvine
10. University of California, Los Angeles
11. University of California, Santa Cruz
12. Yale University
13. Northwestern University
14. Lehigh University
15. Harvard-Smithsonian Center for Astrophysics
16. Hazelwood Observatory, Australia
17. Perth Exoplanet Survey Telescope Observatory
18. Villa '39 Observatory
19. Ames Research Center
20. Massachusetts Institute of Technology
21. Infrared Processing and Analysis Center
22. Washington University in St. Louis
23. Space Telescope Science Institute
24. W.M. Keck Observatory
25. Astrophysics & Space Institute, Schmidt Sciences
26. Macquarie University

Abstract

The degree of alignment between a star's spin axis and the orbital plane of its planets (the stellar obliquity) is related to interesting and poorly understood processes that occur during planet formation and evolution. Hot Jupiters orbiting hot stars (≳6250 K) display a wide range of obliquities, while similar planets orbiting cool stars are preferentially aligned. Tidal dissipation is expected to be more rapid in stars with thick convective envelopes, potentially explaining this trend. Evolved stars provide an opportunity to test the damping hypothesis, particularly stars that were hot on the main sequence and have since cooled and developed deep convective envelopes. We present the first systematic study of the obliquities of hot Jupiters orbiting subgiants that recently developed convective envelopes using Rossiter–McLaughlin observations. Our sample includes two newly discovered systems in the Giants Transiting Giants survey (TOI-6029 b, TOI-4379 b). We find that the orbits of hot Jupiters orbiting subgiants that have cooled below ∼6250 K are aligned or nearly aligned with the spin axis of their host stars, indicating rapid tidal realignment after the emergence of a stellar convective envelope. We place an upper limit for the timescale of realignment for hot Jupiters orbiting subgiants at ∼500 Myr. Comparison with a simplified tidal evolution model shows that obliquity damping needs to be ∼4 orders of magnitude more efficient than orbital period decay to damp the obliquity without destroying the planet, which is consistent with recent predictions for tidal dissipation from inertial waves excited by hot Jupiters on misaligned orbits.

Copyright and License

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

N.S. acknowledges support by the National Science Foundation Graduate Research Fellowship Program under grant Nos. 1842402 and 2236415. A.C. and D.H. acknowledge support from the National Aeronautics and Space Administration (80NSSC21K0652). D.H. acknowledges support from the Alfred P. Sloan Foundation and the Australian Research Council (FT200100871). M.R. is supported by Heising-Simons grant No. 2023-4478. K.A.C. and C.N.W. acknowledge support from the TESS mission via subaward s3449 from MIT. T.D. acknowledges support by the McDonnell Center for the Space Sciences at Washington University in St. Louis. J.M.A.M. is supported by the National Science Foundation (NSF) Graduate Research Fellowship Program (GRFP) under grant No. DGE-1842400.

This paper made use of data collected by the TESS mission and that are publicly available from the Mikulski Archive for Space Telescopes (MAST) operated by the Space Telescope Science Institute (STScI). Funding for the TESS mission is provided by NASA's Science Mission Directorate. We acknowledge the use of public TESS data from pipelines at the TESS Science Office and at the TESS Science Processing Operations Center. Resources supporting this work were provided by the NASA High-End Computing (HEC) Program through the NASA Advanced Supercomputing (NAS) Division at Ames Research Center for the production of the SPOC data products. Funding for the TESS mission is provided by NASA's Science Mission Directorate.

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.

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.

This work makes use of observations from the LCOGT network. Part of the LCOGT telescope time was granted by NOIRLab through the Mid-Scale Innovations Program (MSIP). MSIP is funded by NSF.

Some of the observations in this paper made use of the High-Resolution Imaging instrument Zorro and were obtained under Gemini LLP proposal No. GN/S-2021A-LP-105. Zorro was funded by the NASA Exoplanet Exploration Program and built at the NASA Ames Research Center by Steve B. Howell, Nic Scott, Elliott P. Horch, and Emmett Quigley. Zorro was mounted on the Gemini South telescope of the international Gemini Observatory, a program of NSF's OIR Lab, which is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation, on behalf of the Gemini partnership: the National Science Foundation (United States), National Research Council (Canada), Agencia Nacional de Investigación y Desarrollo (Chile), Ministerio de Ciencia, Tecnología e Innovación (Argentina), Ministério da Ciência, Tecnologia, Inovações e Comunicações (Brazil), and Korea Astronomy and Space Science Institute (Republic of Korea).

This research has made use of the Exoplanet Follow-up Observation Program (ExoFOP; NExScI 2022) website, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program.

Software References

Lightkurve (Lightkurve Collaboration et al. 2018), Astropy (Astropy Collaboration et al. 2013; Price-Whelan et al. 2018; Astropy Collaboration et al. 2022), Astroquery (Ginsburg et al. 2019), GNU Parallel (Tange 2018).

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