The GAPS Programme at TNG. XXXII. The revealing non-detection of metastable HeI in the atmosphere of the hot Jupiter WASP-80b
Journal
Date Issued
2022
Author(s)
Fossati, L.
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Shaikhislamov, I. F.
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Carleo, I.
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Cecchi-Pestellini, C.
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Khodachenko, M. L.
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Efimov, M. A.
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Rumenskikh, M. S.
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Miroshnichenko, I. B.
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Berezutsky, A. G.
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Brogi, M.
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Mancini, L.
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Carosati, D.
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Fiorenzano, A.
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Harutyunyan, A.
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Pedani, M.
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Piotto, G.
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Stoev, H.
Abstract
The hot Jupiter WASP-80b has been identified as a possible excellent target
for detecting and measuring HeI absorption in the upper atmosphere. We observed
4 primary transits of WASP-80b in the optical and near-IR using the HARPS-N and
GIANO-B high-resolution spectrographs, focusing on the HeI triplet. We further
employed a three-dimensional hydrodynamic aeronomy model to understand the
observational results. We did not find any signature of planetary absorption at
the position of the HeI triplet with an upper limit of 0.7% (i.e. 1.11
planetary radii; 95% confidence level). We re-estimated the stellar high-energy
emission that we combined with a stellar photospheric model to generate the
input for the hydrodynamic modelling. We obtained that, assuming a solar He to
H abundance ratio, HeI absorption should have been detected. Considering a
stellar wind 25 times weaker than solar, we could reproduce the non-detection
only assuming a He to H abundance ratio about 16 times smaller than solar.
Instead, considering a stellar wind 10 times stronger than solar, we could
reproduce the non-detection only with a He to H abundance ratio about 10 times
smaller than solar. We attempted to understand this result by collecting all
past HeI measurements looking for correlations with stellar high-energy
emission and planetary gravity, but without finding any. WASP-80b is not the
only planet with a sub-solar estimated He to H abundance ratio, suggesting the
presence of efficient physical mechanisms (e.g. phase separation, magnetic
fields) capable of significantly modifying the He to H content in the upper
atmosphere of hot Jupiters. The planetary macroscopic properties and the shape
of the stellar spectral energy distribution are not sufficient for predicting
the presence or absence of detectable metastable He in a planetary atmosphere,
as also the He abundance appears to play a major role.
Volume
658
Start page
A136
Issn Identifier
0004-6361
Rights
open.access
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