TOI-2196 b: Rare planet in the hot Neptune desert transiting a G-type star

Creators: Persson, Carina M.¹; Georgieva, Iskra Y.¹; Gandolfi, Davide²; Acuna, Lorena³; Aguichine, Artem³; Muresan, Alexandra¹; Guenther, Eike⁴; Livingston, John^{5, 6}; Collins, Karen A.⁷; Dai, Fei⁸; Fridlund, Malcolm^{1, 9}; Goffo, Elisa^{2, 4}; Jenkins, James S.¹⁰; Kabáth, Petr¹¹; Korth, Judith¹; Levine, Alan M.¹²; Serrano, Luisa M.²; Vines, José; Barragan, Oscar¹³; Carleo, Ilaria¹⁴; Colon, Knicole D.¹⁵; Cochran, William D.¹⁶; Christiansen, Jessie L.^{8, 17}; Deeg, Hans J.^{14, 18}; Deleuil, Magali³; Dragomir, Diana¹⁹; Esposito, Massimiliamo⁴; Gan, Tianjun²⁰; Grziwa, Sascha²¹; Hatzes, Artie P.⁴; Hesse, Katharine¹²; Horne, Keith²²; Jenkins, Jon M.²³; Kielkopf, John F.²⁴; Klagyivik, P.²⁵; Lam, Kristine W. F.²⁶; Latham, David W.⁷; Luque, Rafa²⁷; Orell-Miquel, Jaume^{14, 18}; Mortier, Annelies²⁸; Mousis, Olivier³; Narita, Noria^{14, 29}; Osborne, Hannah L. M.³⁰; Palle, Enric¹⁴; Papini, Riccardo³¹; Ricker, George R.¹²; Schmerling, Hendrik²¹; Seager, Sara¹²; Stassun, Keivan G.³²; Van Eylen, Vincent³⁰; Vanderspek, Roland¹²; Wang, Gavin³³; Winn, Joshua N.³⁴; Wohler, Bill^{23, 35}; Zambelli, Roberto³⁶; Ziegler, Carl³⁷

1. Chalmers University of Technology
2. University of Turin
3. Aix Marseille Université, Institut Origines, CNRS, CNES, LAM, Marseille, France
4. Thüringer Landessternwarte Tautenburg
5. National Astronomical Observatory of Japan
6. The Graduate University for Advanced Studies, SOKENDAI
7. Harvard-Smithsonian Center for Astrophysics
8. California Institute of Technology
9. Leiden University
10. Diego Portales University
11. Astronomical Institute
12. Massachusetts Institute of Technology
13. University of Oxford
14. Instituto de Astrofísica de Canarias
15. Goddard Space Flight Center
16. The University of Texas at Austin
17. Infrared Processing and Analysis Center
18. University of La Laguna
19. University of New Mexico
20. Tsinghua University
21. Rhenish Institute for Environmental Research
22. University of St Andrews
23. Ames Research Center
24. University of Louisville
25. Freie Universität Berlin
26. German Aerospace Center
27. University of Chicago
28. University of Cambridge
29. University of Tokyo
30. University College London
31. Wild Boar Remote Observatory, San Casciano in val di Pesa, Firenze, 50026, Italy
32. Vanderbilt University
33. Tsinghua International School, Beijing, 100084, PR China
34. Princeton University
35. Search for Extraterrestrial Intelligence
36. Societá Astronomica Lunae, Castelnuovo Magra, Italy
37. Stephen F. Austin State University

Abstract

The hot Neptune desert is a region hosting a small number of short-period Neptunes in the radius-instellation diagram. Highly irradiated planets are usually either small (R ≲ 2 R_⊕) and rocky or they are gas giants with radii of ≳1 R_J. Here, we report on the intermediate-sized planet TOI-2196 b (TIC 372172128.01) on a 1.2 day orbit around a G-type star (V = 12.0, [Fe/H] = 0.14 dex) discovered by the Transiting Exoplanet Survey Satellite in sector 27. We collected 41 radial velocity measurements with the HARPS spectrograph to confirm the planetary nature of the transit signal and to determine the mass. The radius of TOI-2196 b is 3.51 ± 0.15 R_⊕, which, combined with the mass of 26.0 ± 1.3 M_⊕, results in a bulk density of 3.31_−0.43^+0.51 g cm⁻³. Hence, the radius implies that this planet is a sub-Neptune, although the density is twice than that of Neptune. A significant trend in the HARPS radial velocity measurements points to the presence of a distant companion with a lower limit on the period and mass of 220 days and 0.65 M_J, respectively, assuming zero eccentricity. The short period of planet b implies a high equilibrium temperature of 1860 ± 20 K, for zero albedo and isotropic emission. This places the planet in the hot Neptune desert, joining a group of very few planets in this parameter space discovered in recent years. These planets suggest that the hot Neptune desert may be divided in two parts for planets with equilibrium temperatures of ≳1800 K: a hot sub-Neptune desert devoid of planets with radii of ≈ 1.8−3 R_⊕ and a sub-Jovian desert for radii of ≈5−12 R_⊕. More planets in this parameter space are needed to further investigate this finding. Planetary interior structure models of TOI-2196 b are consistent with a H/He atmosphere mass fraction between 0.4% and 3%, with a mean value of 0.7% on top of a rocky interior. We estimated the amount of mass this planet might have lost at a young age and we find that while the mass loss could have been significant, the planet had not changed in terms of character: it was born as a small volatile-rich planet and it remains one at present.

Copyright and License

© C. M. Persson et al. 2022. Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Acknowledgement

This paper includes data collected by the TESS mission. Funding for the TESS mission is provided by the NASA Explorer Program. 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. 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). This work uses observations made with ESO 3.6-m telescope at La Silla Observatory under programme ID 106.21TJ.001. We are grateful to the ESO staff members for their support during the observations, and to François Bouchy and Xavier Dumusque for coordinating the HARPS time sharing agreement. This work has made use of SME package, which benefits from the continuing development work by J. Valenti and N. Piskunov and we gratefully acknowledge their continued support. (Kupka et al. 2000; Ryabchikova et al. 2015). to page 5 C.M.P., M.F., I.G., and J.K. gratefully acknowledges the support of the Swedish National Space Agency (DNR 65/19, 174/18, 177/19, 2020-00104). L.M.S and D.G. gratefully acknowledge financial support from the CRT foundation under Grant No. 2018.2323 “Gaseous or rocky? Unveiling the nature of small worlds”. P.K. acknowledges support from grant LTT-20015. E.G. acknowledges the support of the Thüringer Ministerium für Wirtschaft, Wissenschaft und Digitale Gesellschaft. J.S.J. greatfully acknowledges support by FONDECYT grant 1201371 and from the ANID BASAL projects ACE210002 and FB210003. H.J.D. acknowledges support from the Spanish Research Agency of the Ministry of Science and Innovation (AEIMICINN) under grant PID2019-107061GB-C66, DOI: 10.13039/501100011033. D.D. acknowledges support from the TESS Guest Investigator Program grants 80NSSC21K0108 and 80NSSC22K0185. M.E. acknowledges the support of the DFG priority program SPP 1992 “Exploring the Diversity of Extrasolar Planets” (HA 3279/12-1). K.W.F.L. was supported by Deutsche Forschungsgemeinschaft grants RA714/14-1 within the DFG Schwerpunkt SPP 1992, Exploring the Diversity of Extrasolar Planets. N.N. acknowledges support from JSPS KAKENHI Grant Number JP18H05439, JST CREST Grant Number JPMJCR1761. M.S.I.P. is funded by NSF.

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