A Testbed for Tidal Migration: The 3D Architecture of an Eccentric Hot Jupiter HD 118203 b Accompanied by a Possibly Aligned Outer Giant Planet

Creators: Zhang 张, Jingwen 婧雯¹; Huber, Daniel^{1, 2}; Weiss, Lauren M.³; Xuan, Jerry W.⁴; Burt, Jennifer A.⁵; Dai, Fei¹; Saunders, Nicholas¹; Petigura, Erik A.⁶; Rubenzahl, Ryan A.⁴; Winn, Joshua N.⁷; Wang, Sharon X.⁸; Van Zandt, Judah⁶; Brodheim, Max⁹; Claytor, Zachary R.^{10, 11}; Crossfield, Ian¹²; Deich, William¹³; Fulton, Benjamin J.⁴; Gibson, Steven R.⁴; Halverson, Samuel⁵; Hill, Grant M.⁹; Holden, Bradford¹³; Householder, Aaron¹⁴; Howard, Andrew W.⁴; Isaacson, Howard¹⁵; Kaye, Stephen⁴; Lanclos, Kyle⁹; Laher, Russ R.¹⁶; Lubin, Jack⁶; Payne, Joel⁹; Roy, Arpita¹⁷; Schwab, Christian¹⁸; Shaum, Abby P.⁴; Walawender, Josh⁹; Wishnow, Edward¹⁵; Yeh, Sherry⁹

1. University of Hawaii at Manoa
2. University of Sydney
3. University of Notre Dame
4. California Institute of Technology
5. Jet Propulsion Lab
6. University of California, Los Angeles
7. Princeton University
8. Tsinghua University
9. W.M. Keck Observatory
10. Space Telescope Science Institute
11. University of Florida
12. University of Kansas
13. University of California, Santa Cruz
14. Massachusetts Institute of Technology
15. University of California, Berkeley
16. NASA Exoplanet Science Institute
17. Schmidt Sciences
18. Macquarie University

Abstract

Characterizing outer companions to hot Jupiters plays a crucial role in deciphering their origins. We present the discovery of a long-period giant planet, HD 118203 c (mc=11.79_(−0.63)^(+0.69) MJ, ac=6.28_(−0.11)^(+0.10) au) exterior to a close-in eccentric hot Jupiter HD 118203 b (P_b = 6.135 days, m_b = 2.14 ± 0.12 M_J, r_b = 1.14 ± 0.029 R_J, e_b = 0.31 ± 0.007) based on 20 yr radial velocities (RVs). Using Rossiter–McLaughlin (RM) observations from the Keck Planet Finder, we measured a low sky-projected spin–orbit angle λb=−11∘7_(−10.0)^(+7.6) for HD 118203 b and detected stellar oscillations in the host star, confirming its evolved status. Combining the RM observation with the stellar inclination measurement, we constrained the true spin–orbit angle of HD 118203 b as Ψ_b < 335 (2σ), indicating the orbit normal of the hot Jupiter nearly aligned with the stellar spin axis. Furthermore, by combining RVs and Hipparcos-Gaia astrometric acceleration, we constrained the line-of-sight mutual inclination between the hot Jupiter and the outer planet to be 9.∘8_(−9.3)^(+16.2) at the 2σ level. HD 118203 is one of first hot Jupiter systems where both the true spin–orbit angle of the hot Jupiter and the mutual inclination between inner and outer planets have been determined. Our results are consistent with a system-wide alignment, with low mutual inclinations between the outer giant planet, the inner hot Jupiter, and the host star. This alignment, along with the moderate eccentricity of HD 118203 c, implies that the system may have undergone coplanar high-eccentricity tidal migration. Under this framework, our dynamical analysis suggests an initial semimajor axis of 0.3–3.2 au for the proto–hot Jupiter.

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

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.

J.Z. would like to thank Maximilian N. Günther for helpful suggestion and advice regarding the use of package allesfitter. J.Z. and D.H. acknowledge support from the Alfred P. Sloan Foundation, and the National Aeronautics and Space Administration (80NSSC22K0303). D.H. also acknowledges support from the Alfred P. Sloan Foundation, and the Australian Research Council (FT200100871). J.Z. and L.M.W. acknowledge support from NASA-Keck Key Stragetic Mission Support grant No. 80NSSC19K1475. L.M.W. also acknowledges support from the NASA Exoplanet Research Program through grant 80NSSC23K0269. 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 and ExoFOP, which are operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program.

Facilities

Keck:I - KECK I Telescope, OHP:1.93m - Observatoire de Haute-Provence's 1.93 meter Telescope, TESS - , Gaia - , Hipparcos - .

Software References

allesfitter (M. N. Günther & T. Daylan 2019, 2021) RadVel (B. J. Fulton et al. 2018) TESS-SIP (C. Hedges et al. 2020).

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