Modeling tails of escaping gas in exoplanet atmospheres with Harmonica

Abstract

Exoplanets that reside close to their host stars, and therefore receive substantial amounts of X-ray and ultraviolet radiation, are prone to suffer from strong atmospheric escape. This can lead to the creation of an envelope of escaping gas along the planet's orbital trajectory, often referred to as a tail. When transiting in front of their host star, these tails can not only produce larger depths in the transit light curves, but also introduce significant asymmetries between ingress and egress. Using the publicly available software Harmonica, we present a method to model the light curves of transiting planets surrounded by extended envelopes of escaping gas, and subsequently infer the shape and size of the latter. We apply this method to the JWST NIRISS/SOSS observations of HAT-P-18b, which show pronounced helium tail features in its spectroscopic light curve of the metastable helium triplet at 10830 Å. Our model reveals that, in order to fit the observed light curve of HAT-P-18b, the planet must possess a trailing helium tail of $15.79_{-1.05}^{+1.14}$ planetary radii. We carry out injection-recovery tests to validate the effectiveness of the proposed methodology. We demonstrate that, with sufficient precision, we would be able to fit a multi-layer envelope to the data, which would provide insight into the relative radial variations in the opacity profile.

15 pages, 10 figures, 3 tables. Accepted to APJL

References in corpus (17)

• A giant comet-like cloud of hydrogen escaping the warm Neptune-mass exoplanet GJ 436b
• Lyman-$\alpha$ Transit Spectroscopy and the Neutral Hydrogen Tail of the Hot Neptune GJ436b
• The Stagger-grid: A grid of 3D stellar atmosphere models - IV. Limb darkening coefficients
• Magnetically controlled mass loss from extrasolar planets in close orbits
• Confirmation of WASP-107b's extended Helium atmosphere with Keck II/NIRSPEC
• ExoClock Project III: 450 new exoplanet ephemerides from ground and space observations
• p-winds: an open-source Python code to model planetary outflows and upper atmospheres
• Near-Infrared Transmission Spectroscopy of HAT-P-18b with NIRISS: Disentangling Planetary and Stellar Features in the Era of JWST
• Water and an escaping helium tail detected in the hazy and methane-depleted atmosphere of HAT-P-18b from JWST NIRISS/SOSS
• Stellar Wind Confinement of Evaporating Exoplanet Atmospheres and its Signatures in 1083 nm Observations
• The post-transit tail of WASP-107b observed at 10830A
• Constraining mornings & evenings on distant worlds: a new semi-analytical approach and prospects with transmission spectroscopy
• ExoTiC-LD: thirty seconds to stellar limb-darkening coefficients
• Using helium 10830 Å transits to constrain planetary magnetic fields
• Transmission strings: a technique for spatially mapping exoplanet atmospheres around their terminators
• Observing atmospheric escape in sub-Jovian worlds with JWST
• Cold day-side winds shape large leading streams in evaporating exoplanet atmospheres