The overflowing atmosphere of WASP-121 b: High-resolution He I λ10833 transmission spectroscopy with VLT/CRIRES+
Czesla, S.; Nortmann, L.; Reiners, A.; Shulyak, D.; Piskunov, N.; Schneider, P. C.; Yan, F.; Rengel, M.; Kochukhov, O.; Hatzes, A.; Lavail, A.; Cont, D.; Lesjak, F.; Boldt-Christmas, L.; Seemann, U.; Nail, F.; Wilson, D. J.
Germany, Netherlands, France, Sweden, Spain, United States, China
Abstract
Transmission spectroscopy is a prime method to study the atmospheres of extrasolar planets. We obtained a high-resolution spectral transit time series of the hot Jupiter WASP-121 b with CRIRES+ to study its atmosphere via transmission spectroscopy of the He I λ10833 triplet lines. Our analysis shows a prominent He I λ10833 absorption feature moving along with the planetary orbital motion, which shows an observed, transit-averaged equivalent width of approximately 30 mÅ, a slight redshift, and a depth of about 2%, which can only be explained by an atmosphere overflowing its Roche lobe. We carried out 3D hydrodynamic modeling to reproduce the observations, which favors asymmetric mass loss with a more pronounced leading tidal tail, possibly also explaining observational evidence for additional absorption stationary in the stellar rest frame. A trailing tail is not detectable. From our modeling, we derived estimates of ≥2 × 1013 g s‑1 for the stellar and 5.4 × 1012 g s‑1 for the planetary mass loss rate, which is consistent with X-ray and extreme-ultraviolet (XUV) driven mass loss in WASP-121 b.