TOI-2196 b: Rare planet in the hot Neptune desert transiting a G-type star
Creators: name: Persson, Carina M.
name: Georgieva, Iskra Y.
name: Gandolfi, Davide
name: Acuña, Lorena
name: Aguichine, Artem
name: Muresan, Alexandra
name: Guenther, Eike
name: Livingston, John
name: Collins, Karen A.
name: Fridlund, Malcolm
name: Goffo, Elisa
name: Jenkins, James S.
name: Kabáth, Petr
name: Korth, Judith
name: Levine, Alan M.
name: Serrano, Luisa M.
name: Vines, José
name: Barragán, Oscar
name: Carleo, Ilaria
name: Colon, Knicole D.
name: Cochran, William D.
name: Christiansen, Jessie L.
name: Deeg, Hans J.
name: Deleuil, Magali
name: Dragomir, Diana
name: Esposito, Massimiliamo
name: Gan, Tianjun
name: Grziwa, Sascha
name: Hatzes, Artie P.
name: Hesse, Katharine
name: Horne, Keith
name: Jenkins, Jon M.
name: Kielkopf, John F.
name: Klagyivik, P.
name: Lam, Kristine W. F.
name: Latham, David W.
name: Luque, Rafa
name: Orell-Miquel, Jaume
name: Mortier, Annelies
name: Mousis, Olivier
name: Narita, Noria
name: Osborne, Hannah L. M.
name: Palle, Enric
name: Papini, Riccardo
name: Ricker, George R.
name: Schmerling, Hendrik
name: Seager, Sara
name: Stassun, Keivan G.
name: Van Eylen, Vincent
name: Vanderspek, Roland
name: Wang, Gavin
name: Winn, Joshua N.
name: Wohler, Bill
name: Zambelli, Roberto
name: Ziegler, Carl
Publisher: name: arXiv
Year: 2022
Subjects: subject: Earth and Planetary Astrophysics (astro-ph.EP)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: Highly irradiated planets in the hot Neptune desert are usually either small (R &lt; 2 Rearth) and rocky or they are gas giants with radii of &gt;1 Rjup. Here, we report on the intermediate-sized planet TOI-2196 on a 1.2 day orbit around a G-type star discovered by TESS in sector 27. We collected 42 radial velocity measurements with the HARPS spectrograph to determine the mass. The radius of TOI-2196 b is 3.51 +/- 0.15 Rearth, which, combined with the mass of 26.0 +/- 1.3 Mearth, results in a bulk density of 3.31+0.51-0.43 g/cm3. 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 velocities points to the presence of a distant companion with a lower limit on the period and mass of 220 days and 0.65 Mjup, 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 &gt; 1800 K: a hot sub-Neptune desert devoid of planets with radii of 1.8-3 Rearth and a sub-Jovian desert for radii of 5-12 Rearth. 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.
description: 17 pages, 15 figures, 7 tables, accepted 11 July 2022 for publication in Astronomy &amp; Astrophysics