Year: 2025
Type: article
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-18 b, which show pronounced helium tail features in the 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-18 b, the planet must possess a trailing helium tail of 15.7 9 − 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 multilayer envelope to the data, which would provide insight into the relative radial variations in the opacity profile.
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $2,400
Funders: Smithsonian Institution, “la Caixa” Foundation, Space Telescope Science Institute, Government of the United Kingdom, UK Research and Innovation, Ministerio de Ciencia, Innovación y Universidades, Centres de Recerca de Catalunya, European Commission, Generalitat de Catalunya, Universitat Autònoma de Barcelona, Fundación Bancaria Caixa d'Estalvis i Pensions de Barcelona, Smithsonian Astrophysical Observatory, HORIZON EUROPE Framework Programme, Agència de Gestió d'Ajuts Universitaris i de Recerca, European Regional Development Fund, Agencia Estatal de Investigación
Awards: G1105844351, G1175115578, G118516010, G1255325603, G1353885700, G2038104832, G2064873908, G2262748287, G2462415295, G2499501003, G2601397997, G288263039, G3005324705, G300979063, G302750986, G3261693824, G3320050967, G3480869486, G3522231704, G3546882995, G3681454997, G3715634343, G4019291869, G4042783231, G410571670, G425668148, G451917667, G491712853, G5080475149, G5099673792, G5132640529, G5178665745, G5195188938, G5539308778, G5635532810, G5783525505, G5852091828, G5955501538, G5967599077, G617610489, G6217019444, G6513613686, G6656126374, G7084143925, G7434936867, G7685134749, G7731791180, G7805626310, G7863371703, G8284171658, G8497050386, G8819685017
OpenAlex ID: W4414594199