TOI-2196 b: Rare planet in the hot Neptune desert transiting a G-type star
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aa44118-22.pdf
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Published version
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3.73 MB
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Author(s)
Seager, Sara
Date Issued
2022
Journal
Astronomy and Astrophysics
Publisher
EDP Sciences
Citation
Seager, Sara. 2022. "TOI-2196 b: Rare planet in the hot Neptune desert transiting a G-type star." Astronomy and Astrophysics, 666.
Version
Final published version
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 RJ
. 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+0.51
−0.43 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 MJ
, 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.
MIT Department
Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences
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Creative Commons Attribution 4.0 International license
Persistent DSpace Link
DOI of Published Version
https://doi.org/10.1051/0004-6361/202244118
