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

Abstract

The He I λ10833 Å 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 He I triplet. Although previous studies using lower resolution instruments have reported non-detections of 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 He I, due to telluric H2O 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 2.10−0.50+0.45% (4.6 σ) with a full width at half maximum (FWHM) of 1.30−0.25+0.30 Å. The detection of He I is statistically significant at the 4.6 σ 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) × 1010 g s−1 and an outflow temperature in the range of 2900–4400 K. Further high-resolution follow-up observations of GJ 1214 b are needed to confirm and fully characterise the detection of an extended atmosphere surrounding GJ 1214 b. If confirmed, this would be strong evidence that this planet has a primordial atmosphere accreted from the original planetary nebula. Despite previous intensive observations from space- and ground-based observatories, our He I excess absorption is the first tentative detection of a chemical species in the atmosphere of this benchmark sub-Neptune planet.

A detailed analysis of the Gl 486 planetary system

“…Above the surface and below the tropopause, rotational turbulence mixes the layers of the atmosphere (the Earth's tropopause height varies from about 9 km at the poles to 17 km at the equator), and the mean molecular mass of the "dry air" (without water vapour content) keeps constant. H is also a key input parameter for the equivalent height of the absorbing atmosphere (δ ≈ 2HR b /R 2 ), which is widely used in exoplanet atmosphere studies (e.g., Nortmann et al 2018;Orell-Miquel et al 2022).…”

“…H is also a key input parameter for the equivalent height of the absorbing atmosphere (δ ≈ 2HR b /R 2 ), which is widely used in exoplanet atmosphere studies (e.g. Nortmann et al 2018;Orell-Miquel et al 2022).…”

Modeling the Hα and He 10830 Transmission Spectrum of WASP-52b

“…Up to now, there are several exoplanets with detected excess absorption of this line through transmission spectroscopy; they are WASP-107b, HD 189733b, HD 209458b, GJ 3470b, WASP-69b, HAT-P-11b, HAT-P-32b, and TOI 560.01 (Salz et al 2018;Spake et al 2018;Allart et al 2018;Nortmann et al 2018;Alonso-Floriano et al 2019b;Palle et al 2020;Kirk et al 2020;Ninan et al 2020;Spake et al 2021;Czesla et al 2022;Zhang et al 2022). Tentative detection of He 10830 absorption by the atmosphere of GJ 1214b was also reported recently (Orell-Miquel et al 2022). Models have been developed to interpret the observed signals.…”

Validation and atmospheric exploration of the sub-Neptune TOI-2136b around a nearby M3 dwarf

“…We also obtained a transmission spectrum of the planet around the He i 10830 Å absorption lines. In other works, helium absorption is detected on the atmosphere of three sub-Neptunes (TOI-560.01; Zhang et al 2022, GJ3470b;Palle et al 2020, andGJ1214b;Orell-Miquel et al 2022). To compare our results with previous He i detections in the literature, we calculated the equivalent height of the atmosphere normalized by the scale height.…”

“…To obtain the transmission spectrum, we corrected for these telluric absorption lines, as well as for the stellar RV shift and the planet RV. To obtain an OH − emission model for our data, we fitted the strongest OH − emission line with a Gaussian to estimate the central wavelength, and we compared it with previous works (Palle et al 2020;Orell-Miquel et al 2022) to estimate the central wavelength of other OH − emission lines. The region of the strongest emission was then masked.…”