Discovery of two warm mini-Neptunes with contrasting densities orbiting the young K3V star TOI-815

Article Article scientifique Article Discovery of two warm mini-Neptunes with contrasting densities orbiting the young K3V star TOI-815 eng 2024-04-30 2024-04-30 Collab. collaborator Psaridi Angeliki 0000-0002-4797-2419 942153 collaborator Bouchy François 0000-0002-7613-393X 133687 Département d'astronomie (ASTRO) collaborator Lendl Monika 0000-0001-9699-1459 715612 Département d'astronomie (ASTRO) collaborator Parc Léna Romane Elisa 0000-0002-7382-1913 402592 Département d'astronomie (ASTRO) collaborator Billot Nicolas 0000-0003-3429-3836 861787 Département d'astronomie (ASTRO) collaborator Chakraborty Hritam 0000-0002-5177-1898 973565 Département d'astronomie (ASTRO) collaborator Grieves Nolan 0000-0001-8105-0373 930970 collaborator Heitzmann Alexis 0000-0002-8091-7526 415715 Département d'astronomie (ASTRO) collaborator Krenn Andreas 0000-0003-3615-4725 968475 collaborator Venturini Julia 0000-0001-9527-2903 984012 Département d'astronomie (ASTRO) collaborator Ulmer-Moll Solène 0000-0003-2417-7006 943255 collaborator Allart Romain 0000-0002-1199-9759 751868 collaborator Alonso Sobrino Roi 0000-0001-8462-8126 690729 collaborator Beck Mathias 0000-0003-3926-0275 133384 collaborator Bourrier Vincent 0000-0002-9148-034X 828250 Département d'astronomie (ASTRO) collaborator Cointepas Marion 934336 Département d'astronomie (ASTRO) collaborator Lo Curto Gaspare 0000-0002-1158-9354 665040 collaborator Deline Adrien 797061 Département d'astronomie (ASTRO) collaborator Delrez Laetitia 0000-0001-6108-4808 932714 collaborator Demory Brice-Olivier 0000-0002-9355-5165 629568 collaborator Dumusque Xavier 0000-0002-9332-2011 583253 Département d'astronomie (ASTRO) collaborator Ehrenreich David 0000-0001-9704-5405 789146 Département d'astronomie (ASTRO) collaborator Gillon Michael 0000-0003-1462-7739 642673 collaborator Hagelberg Janis 0000-0002-1096-1433 538499 collaborator Lavie Baptiste 0000-0001-8884-9276 861546 Département d'astronomie (ASTRO) collaborator Lovis Christophe 0000-0001-7120-5837 134919 Département d'astronomie (ASTRO) collaborator Segransan Damien 134301 Département d'astronomie (ASTRO) collaborator Udry Stéphane 23409 Département d'astronomie (ASTRO) A5 10.1051/0004-6361/202348678 0004-6361 https://www.aanda.org/10.1051/0004-6361/202348678 We present the discovery and characterization of two warm mini-Neptunes transiting the K3V star TOI-815 in a K–M binary system. Analysis of its spectra and rotation period reveal the star to be young, with an age of 200 −200 +400 Myr. TOI-8l5b has a 11.2-day period and a radius of 2.94 ± 0.05 R ⊕ with transits observed by TESS, CHEOPS, ASTEP, and LCOGT. The outer planet, TOI-8l5c, has a radius of 2.62 ± 0.10 R ⊕ , based on observations of three nonconsecutive transits with TESS; targeted CHEOPS photometry and radial velocity follow-up with ESPRESSO were required to confirm the 35-day period. ESPRESSO confirmed the planetary nature of both planets and measured masses of 7.6 ± 1.5 M ⊕ ( ρ P = 1.64 −0.31 +0.33 g cm −3 ) and 23.5 ± 2.4 M ⊕ ( ρ P = 7.2 −1.0 +1.1 g cm −3 ), respectively. Thus, the planets have very different masses, which is unusual for compact multi-planet systems. Moreover, our statistical analysis of mini-Neptunes orbiting FGK stars suggests that weakly irradiated planets tend to have higher bulk densities compared to those undergoing strong irradiation. This could be ascribed to their cooler atmospheres, which are more compressed and denser. Internal structure modeling of TOI-815b suggests it likely has a H-He atmosphere that constitutes a few percent of the total planet mass, or higher if the planet is assumed to have no water. In contrast, the measured mass and radius of TOI-815c can be explained without invoking any atmosphere, challenging planetary formation theories. Finally, we infer from our measurements that the star is viewed close to pole-on, which implies a spin-orbit misalignment at the 3 σ level. This emphasizes the peculiarity of the system’s orbital architecture, and probably hints at an eventful dynamical history. Dewey 520 26 Département d'astronomie 12 false Astronomy & astrophysics 685 164348fa-6d95-44e7-bb3a-7f528298d07f Article (Published version) Public Article_scientifique_from_crossref.pdf 19427128 application/pdf CC BY-4.0 cd7a845c3cde447c142066e92faab5632fb93259b186c5090bbd946150b7df9a openAccess Faculté des sciences / Département d'astronomie

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Discovery of two warm mini-Neptunes with contrasting densities orbiting the young K3V star TOI-815	Astronomy & astrophysics			2024	24	144

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Krenn, Andreas