The Posttransit Tail of WASP-107b Observed at 10830 Å

J. J. Spake,A. Oklopčić,L. A. Hillenbrand

doi:10.3847/1538-3881/ac178a

Abstract

Abstract Understanding the effects of high-energy radiation and stellar winds on planetary atmospheres is vital for explaining the observed properties of close-in exoplanets. Observations of transiting exoplanets in the triplet of metastable helium lines at 10830 Å allow extended atmospheres and escape processes to be studied for individual planets. We observed one transit of WASP-107b with NIRSPEC on Keck at 10830 Å. Our observations, for the first time, had significant posttransit phase coverage, and we detected excess absorption for over an hour after fourth contact. The data can be explained by a comet-like tail extending out to ∼7 planet radii, which corresponds to roughly twice the Roche lobe radius of the planet. Planetary tails are expected based on three-dimensional simulations of escaping exoplanet atmospheres, particularly those including the interaction between the escaped material and strong stellar winds, and have been previously observed at 10830 Å in at least one other exoplanet. With both the largest midtransit absorption signal and the most extended tail observed at 10830 Å, WASP-107b remains a keystone exoplanet for atmospheric escape studies.

Highlights

Most known transiting exoplanets orbit close to their host stars and are highly irradiated, which makes them likely susceptible to atmospheric escape
The excess absorption calculated this way is dramatically less than that reported by Kirk et al (2020), and the peak appears redshifted in comparison
To summarize: we detected a transit of WASP-107b at 10830 Å, with an in-transit absorption spectrum (Figure 6, top panel) consistent with previously published results; we demonstrated asymmetry in the transit light curves; and we found evidence for blueshifted, posttransit absorption at 10830 Å

Summary

Introduction

Most known transiting exoplanets orbit close to their host stars and are highly irradiated, which makes them likely susceptible to atmospheric escape. The Lyα line of ground-state hydrogen was the first absorption line used to find exoplanet atmospheres overflowing their Roche radii, for the hot-Jupiters HD209458b (Vidal-Madjar et al 2003) and HD189733b (Lecavelier Des Etangs et al 2010). The Hα line, from the first excited state of hydrogen, has been used to observe the high-altitude thermospheres of exoplanets, where mass loss is thought to be launched (e.g., Jensen et al 2012; Yan & Henning 2018). But still abundant elements, like carbon, oxygen, magnesium, and iron, have been observed overflowing (or close to) the Roche radii of some planets (e.g., Vidal-Madjar et al 2004, 2013; Sing et al 2019)

Results

Discussion

Conclusion