Confirmation of an He I evaporating atmosphere around the 650-Myr-old sub-Neptune HD 235088 b (TOI-1430 b) with CARMENES

DOI: 
10.1051/0004-6361/202346445
Publication date: 
11/09/2023
Main author: 
Orell-Miquel, J.
IAA authors: 
Lampón, M.;López-Puertas, M.;Amado, P. J.;Sánchez-López, A.
Authors: 
Orell-Miquel, J.;Lampón, M.;López-Puertas, M.;Mallorquín, M.;Murgas, F.;Peláez-Torres, A.;Pallé, E.;Esparza-Borges, E.;Sanz-Forcada, J.;Tabernero, H. M.;Nortmann, L.;Nagel, E.;Parviainen, H.;Zapatero Osorio, M. R.;Caballero, J. A.;Czesla, S.;Cifuentes, C.;Morello, G.;Quirrenbach, A.;Amado, P. J.;Fernández-Martín, A.;Fukui, A.;Henning, Th.;Kawauchi, K.;de Leon, J. P.;Molaverdikhani, K.;Montes, D.;Narita, N.;Reiners, A.;Ribas, I.;Sánchez-López, A.;Schweitzer, A.;Stangret, M.;Yan, F.
Journal: 
Astronomy and Astrophysics
Publication type: 
Article
Volume: 
677
Pages: 
A56
Abstract: 
HD 235088 (TOI-1430) is a young star known to host a sub-Neptune-sized planet candidate. We validated the planetary nature of HD 235088 b with multiband photometry, refined its planetary parameters, and obtained a new age estimate of the host star, placing it at 600-800 Myr. Previous spectroscopic observations of a single transit detected an excess absorption of He I coincident in time with the planet candidate transit. Here, we confirm the presence of He I in the atmosphere of HD 235088 b with one transit observed with CARMENES. We also detected hints of variability in the strength of the helium signal, with an absorption of −0.91 ± 0.11%, which is slightly deeper (2σ) than the previous measurement. Furthermore, we simulated the He I signal with a spherically symmetric 1D hydrodynamic model, finding that the upper atmosphere of HD 235088 b escapes hydrodynamically with a significant mass loss rate of (1.5−5) × 10<SUP>10</SUP> g s<SUP>−1</SUP> in a relatively cold outflow, with T = 3125 ±375 K, in the photon-limited escape regime. HD 235088 b (R<SUB>p</SUB> = 2.045 ± 0.075 R<SUB>⊕</SUB>) is the smallest planet found to date with a solid atmospheric detection - not just of He I but any other atom or molecule. This positions it a benchmark planet for further analyses of evolving young sub-Neptune atmospheres.
Database: 
ADS
URL: 
https://ui.adsabs.harvard.edu/#abs/2023A&A...677A..56O/abstract
ADS Bibcode: 
2023A&A...677A..56O
Keywords: 
planets and satellites: atmospheres;stars: individual: HD 235088;planets and satellites: individual: HD 235088 b;techniques: photometric;techniques: spectroscopic;Astrophysics - Earth and Planetary Astrophysics