Probing atmospheric escape through metastable He I triplet lines in 15 exoplanets observed with SPIRou

Abstract

For several years, the metastable helium triplet line has been successfully used as a tracer toprobe 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. This work aims to search for the He triplet signature in fifteen transiting exoplanets, ranging from super-Earths to ultra-hot Jupiters, and observed with SPIRou, a high-resolution (R ∼70 000) near- infrared spectropolarimeter at the CFHT, to bring new constraints or to improve the 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 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 non-detections. We notably report improved constraints on the mass loss rate and temperature of the escaping gas for TOI-1807 b, and report a non-detection 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 non-detection 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.