Simulation of 10830 {\AA} absorption with a 3D hydrodynamic model reveals the solar He abundance in upper atmosphere of WASP-107b

TL;DR

This study uses a 3D hydrodynamic model to simulate the HeI 10830 Å absorption in WASP-107b's atmosphere, accurately reproducing observations and constraining the helium abundance and stellar XUV flux.

Contribution

It introduces a self-consistent 3D multi-fluid hydrodynamic model that explains the HeI absorption profiles and constrains atmospheric parameters of WASP-107b.

Findings

HeI absorption profiles are reproduced within observational accuracy.

Stellar XUV flux is constrained to (6-10) erg cm-2 s-1 at 1 AU.

Helium abundance in the upper atmosphere is estimated to be 0.075-0.15.

Abstract

Transmission spectroscopy of WASP-107b revealed 7-8% absorption at the position of metastable HeI triplet at 10830 {\AA} in Doppler velocity range of [-20; 10] km/s, which is stronger than that measured in other exoplanets. With a dedicated 3D self-consistent hydrodynamic multi-fluid model we calculated the expanding upper atmosphere of WASP-107b and reproduced within the observations accuracy the measured HeI absorption profiles, constraining the stellar XUV flux to (6-10) erg cm-2 s-1 at 1 a.u., and the upper atmosphere helium abundance He/H to 0.075-0.15. The radiation pressure acting on the metastable HeI atoms was shown to be an important factor affecting the shape of the absorption profiles. Its effect is counterbalanced by the processes of collisional depopulation of the HeI metastable state. Altogether, the observed HeI absorption in WASP-107b can be interpreted with the expected reasonable parameters of the stellar-planetary system and appropriate account of the electron and atom impact processes.