1 research outputs found
Confirmation of an He I evaporating atmosphere around the 650-Myr-old sub-Neptune HD235088 b (TOI-1430 b) with CARMENES
HD235088 (TOI-1430) is a young star known to host a sub-Neptune-sized planet
candidate. We validated the planetary nature of HD235088 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 HD235088 b with one transit observed with
CARMENES. We also detected hints of variability in the strength of the helium
signal, with an absorption of 0.910.11%, which is slightly deeper
(2) than the previous measurement. Furthermore, we simulated the He I
signal with a spherically symmetric 1D hydrodynamic model, finding that the
upper atmosphere of HD235088 b escapes hydrodynamically with a significant mass
loss rate of (1.5-5) 10g s, in a relatively cold outflow,
with =3125375 K, in the photon-limited escape regime. HD235088 b
( = 2.0450.075 R) 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.Comment: Accepted for publication in A&A. 17 pages, 18 figure