paper

A tentative detection of He I in the atmosphere of GJ 1214b

arXiv:2201.11120 · doi:10.1051/0004-6361/202142455

Abstract

The $\ion{He}{I}$ 10833\, triplet is a powerful tool for characterising the upper atmosphere of exoplanets and tracing possible mass loss. Here, we analysed one transit of GJ\,1214\,b observed with the CARMENES high-resolution spectrograph to study its atmosphere via transmission spectroscopy around the $\ion{He}{I}$ triplet. Although previous studies using lower resolution instruments have reported non-detections of $\ion{He}{I}$ in the atmosphere of GJ\,1214\,b, we report here the first potential detection. We reconcile the conflicting results arguing that previous transit observations did not present good opportunities for the detection of $\ion{He}{I}$, due to telluric HO absorption and OH emission contamination.We simulated those earlier observations, and show evidence that the planetary signal was contaminated. From our single non-telluric-contaminated transit, we determined an excess absorption of 2.10\,\% (4.6\,) with a full width at half maximum (FWHM) of 1.30\,Å. The detection of \ion{He}{I} is statistically significant at the 4.6\, level, but repeatability of the detection could not be confirmed due to the availability of only one transit. By applying a hydrodynamical model and assuming an H/He composition of 98/2, we found that GJ\,1214\,b would undergo hydrodynamic escape in the photon-limited regime, losing its primary atmosphere with a mass-loss rate of (1.5--18)\,\,10\,g\,s and an outflow temperature in the range of 2900--4400\,K. Our $\ion{He}{I}$ excess absorption is the first tentative detection of a chemical species in the atmosphere of this benchmark sub-Neptune planet.

Accepted for publication in A&A. 12 pages, 7 figures

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