Tidally Heated Sub-Neptunes, Refined Planetary Compositions, and Confirmation of a Third Planet in the TOI-1266 System

Creators: Greklek-McKeon, Michael¹; Vissapragada, Shreyas²; Knutson, Heather A.¹; Fukui, Akihiko^{3, 4}; Saidel, Morgan¹; Gomez Barrientos, Jonathan¹; Levine, W. Garrett⁵; Behmard, Aida⁶; Batygin, Konstantin¹; Chachan, Yayaati⁷; Vasisht, Gautam⁸; Hu, Renyu^{1, 8}; Cloutier, Ryan⁹; Latham, David¹⁰; López-Morales, Mercedes¹¹; Vanderburg, Andrew¹²; Heffner, Carolyn¹; Nied, Paul¹; Milburn, Jennifer¹; Wilson, Isaac¹; Roderick, Diana¹; Koviak, Kathleen¹; Barlow, Tom¹; Stone, John F.¹; Kiman, Rocio¹; Korth, Judith¹³; de Leon, Jerome P.³; Fukuda, Izuru³; Hayashi, Yuya³; Ikoma, Masahiro¹⁴; Ikuta, Kai³; Isogai, Keisuke^{3, 15}; Kawai, Yugo³; Kawauchi, Kiyoe¹⁶; Kusakabe, Nobuhiko¹⁴; Livingston, John H.^{14, 17}; Mori, Mayuko¹⁴; Narita, Norio^{4, 3}; Tamura, Motohide^{3, 14}; Watanabe, Noriharu³; Fernández-Rodríguez, Gareb^{4, 18}

1. California Institute of Technology
2. Carnegie Science Observatories, Pasadena, CA 91101, USA
3. University of Tokyo
4. Instituto de Astrofísica de Canarias
5. Yale University
6. American Museum of Natural History
7. McGill University
8. Jet Propulsion Lab
9. McMaster University
10. Harvard-Smithsonian Center for Astrophysics
11. Space Telescope Science Institute
12. Massachusetts Institute of Technology
13. Lund University
14. National Astronomical Observatory of Japan
15. Kyoto University
16. Ritsumeikan University
17. The Graduate University for Advanced Studies, SOKENDAI
18. University of La Laguna

Abstract

TOI-1266 is a benchmark system of two temperate (<450 K) sub-Neptune-sized planets orbiting a nearby M dwarf exhibiting a rare inverted architecture with a larger interior planet. In this study, we characterize transit timing variations (TTVs) in the TOI-1266 system using high-precision ground-based follow-up and new TESS data. We confirm the presence of a third exterior nontransiting planet, TOI-1266 d (P = 32.5 days, M_d = 3.68−1.11+1.05M⊕), and combine the TTVs with archival radial velocity measurements to improve our knowledge of the planetary masses and radii. We find that, consistent with previous studies, TOI-1266 b (R_b = 2.52 ± 0.08 R_⊕, M_b = 4.46 ± 0.69 M_⊕) has a low bulk density requiring the presence of a hydrogen-rich envelope, while TOI-1266 c (R_c = 1.98 ± 0.10 R_⊕, M_c = 3.17 ± 0.76 M_⊕) has a higher bulk density that can be matched by either a hydrogen-rich or water-rich envelope. Our new dynamical model reveals that this system is arranged in a rare configuration with the inner and outer planets located near the 3:1 period ratio with a nonresonant planet in between them. Our dynamical fits indicate that the inner and outer planet have significantly nonzero eccentricities (eb+ed=0.076−0.019+0.029), suggesting that TOI-1266 b may have an inflated envelope due to tidal heating. Finally, we explore the corresponding implications for the formation and long-term evolution of the system, which contains two of the most favorable cool (<500 K) sub-Neptunes for atmospheric characterization with JWST.

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

We thank the Palomar Observatory telescope operators, support astronomers, hospitality, and administrative staff for their support. We are especially grateful to Monastery keeper Jeff. We thank all of the Palomar chefs—gone from the Monastery but never forgotten—the ones who made observing at Palomar a uniquely pleasant experience among astronomers. Part of this program was supported by JPL Hale telescope time allocations. We are thankful to the PARVI team and Palomar Observatory directorate, especially Chas Beichman, Aurora Kesseli, and Andy Boden for their gracious support of the Palomar TTV survey program during periods requiring quick readjustment of the 200 inch observing schedule. We benefited from useful conversations with Fei Dai, George King, Luke Bouma, and Julie Inglis. Portions of code used to create and edit figures and tables in this manuscript were generated with assistance from Anthropic's Claude 3.5 Sonnet.

This paper is based on observations made with the MuSCAT3 instrument, developed by the Astrobiology Center and under financial support by JSPS KAKENHI (JP18H05439) and JST PRESTO (JPMJPR1775), at Faulkes Telescope North on Maui, HI, operated by the Las Cumbres Observatory. This work is partly supported by JSPS KAKENHI grant Nos. JP21K13955, JP24H00017, JP24K00689, JP24K17083, JP24K17082, and JP24H00248, and JSPS Bilateral Program No. JPJSBP120249910, JSPS Grant-in-Aid for JSPS Fellows grant No. JP24KJ0241, Astrobiology Center SATELLITE Research project AB022006, and JST SPRING, grant No. JPMJSP2108.

This research was supported from the Wilf Family Discovery Fund in Space and Planetary Science established by the Wilf Family Foundation. This research has made use of the NASA Exoplanet Archive and the 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. The research made use of the Swarthmore transit finder online tool (E. Jensen 2013). We acknowledge the use of public TESS data from pipelines at the TESS Science Office and at the TESS Science Processing Operations Center. This paper includes data collected by the TESS mission that are publicly available from the Mikulski Archive for Space Telescopes (MAST) at the Space Telescope Science Institute (STScI). STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Support for MAST for non-HST data is provided by the NASA Office of Space Science via grant NNX13AC07G and by other grants and contracts. The specific TESS sectors used in this work can be accessed via doi:10.17909/d4f2-t519. Funding for the TESS mission is provided by NASA's Science Mission Directorate.

This research made use of exoplanet (D. Foreman-Mackey et al. 2021a, 2021b) and its dependencies (Astropy Collaboration et al. 2013, 2018; J. Salvatier et al. 2016; Theano Development Team 2016; D. Foreman-Mackey et al. 2017; D. Foreman-Mackey 2018; R. Kumar et al. 2019; R. Luger et al. 2019; E. Agol et al. 2020).

Facilities

ADS - , Exoplanet Archive - , TESS - , Hale - Palomar Observatory's 5.1m Hale Telescope, OAO:1.88m - , LCOGT - Las Cumbres Observatory Global Telescope.

Software References

astropy (Astropy Collaboration et al. 2018), scipy (P. Virtanen et al. 2020), numpy (C. R. Harris et al. 2020), matplotlib (J. D. Hunter 2007), rebound (H. Rein & D. Tamayo 2015), BATMAN (L. Kreidberg 2015), emcee (D. Foreman-Mackey et al. 2013), corner (D. Foreman-Mackey 2016), exoplanet (D. Foreman-Mackey et al. 2021a), RadVel (B. J. Fulton et al. 2018), TTVFast (K. M. Deck et al. 2014), reboundx (D. Tamayo et al. 2020), corner (D. Foreman-Mackey 2016), and lightkurve (Lightkurve Collaboration et al. 2018), The Cannon (A. Behmard et al. 2025), Claude 3.5 Sonnet.

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Resource type: Journal Article
Publisher: American Astronomical Society
Published in: Astronomical Journal, 169(6), 292, ISSN: 0004-6256.
Languages: English