Exoplanets & Exomoons

Probing Atmospheric Escape Through Metastable He I Triplet Lines In 15 Exoplanets Observed With SPIRou

By Keith Cowing
Status Report
June 14, 2024
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Probing Atmospheric Escape Through Metastable He I Triplet Lines In 15 Exoplanets Observed With SPIRou
Stellar surface intensity map at 1083.31nm computed with PYSME in the case of HAT-P-11 b. The intensity map is relative to the integrated intensity over the stellar map at 1083.31nm. The grid contains 101×101 cells, and the planet’s trajectory is shown with a red solid line with black dots indicating the planet’s center at each observed phase. The planet solid disk is shown at a given phase, with the underlying stellar cells being excluded from the master spectrum computation. — astro-ph.EP

For several years, the metastable helium triplet line has been successfully used as a tracer to probe atmospheric escape in transiting exoplanets. This absorption in the near-infrared (1083.3 nm) can be observed from the ground using high-resolution spectroscopy, providing new constraints on the mass-loss rate and the temperature characterizing the upper atmosphere of close-in exoplanets.

The aim of this work is to search for the He triplet signature in 15 transiting exoplanets — ranging from super-Earths to ultrahot Jupiters — observed with SPIRou, a high-resolution (R~70 000) near-infrared spectropolarimeter at the CFHT, in order to bring new constraints or to improve existing ones regarding atmospheric escape through a homogeneous study.

We developed a full data processing and analysis pipeline to correct for the residual telluric and stellar contributions. We then used two different 1D models based on the Parker-wind equations and nonlocal thermodynamic equilibrium (NLTE) radiative transfer to interpret the observational results.

We confirm published He triplet detections for HAT-P-11 b, HD 189733 b, and WASP-69 b. We tentatively detect the signature of escaping He in HD 209458 b, GJ 3470 b, and WASP-76 b. We report new constraints on the mass-loss rate and temperature for our three detections and set upper limits for the tentative and nondetections. We notably report improved constraints on the mass-loss rate and temperature of the escaping gas for TOI-1807 b, and report a nondetection for the debated atmospheric escape in GJ 1214 b.

We also conducted the first search for the He signature in GJ 486 b since its discovery and report a nondetection of the He triplet. Finally, we studied the impact of important model assumptions on our retrieved parameters, notably the limitations of 1D models and the influence of the H/He ratio on the derived constraints.

A. Masson, S. Vinatier, B. Bézard, M. López-Puertas, M. Lampón, F. Debras, A. Carmona, B. Klein, E. Artigau, W. Dethier, S. Pelletier, T. Hood, R. Allart, V. Bourrier, C. Cadieux, B. Charnay, N. B. Cowan, N. J. Cook, X. Delfosse, J.-F. Donati, P.-G. Gu, G. Hébrard, E. Martioli, C. Moutou, O. Venot, A. Wyttenbach

Comments: 33 pages, 14 figures
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2406.09225 [astro-ph.EP] (or arXiv:2406.09225v1 [astro-ph.EP] for this version)
Submission history
From: Adrien Masson
[v1] Thu, 13 Jun 2024 15:27:08 UTC (17,230 KB)

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻