J/ApJ/940/L35ivo://CDS.VizieR/J/ApJ/940/L35doi:10.26093/cds/vizier.19409035CDSFu G.Espinoza N.Sing D.K.Lothringer J.D.Dos Santos L.A.,Rustamkulov Z.Deming D.Kempton E.M.-R.Komacek T.D.Knutson H.A.,Albert L.Pontoppidan K.Volk K.Filippazzo J.2025-02-24T20:13:41Z2024-12-13T09:54:57ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frexoplanetsinfrared-astronomyspectroscopyJWST is here. The early release observation (ERO) program provides us with the first look at the scientific data and the spectral capabilities. One of the targets from the ERO is HAT-P-18b, an inflated Saturn-mass planet with an equilibrium temperature of ~850K. We present the NIRISS/SOSS transmission spectrum of HAT-P-18b from 0.6 to 2.8{mu}m and reveal the planet in the infrared beyond 1.6{mu}m for the first time. From the spectrum, we see clear water and escaping helium tail features in an otherwise very hazy atmosphere. Our free chemistry retrievals with ATMO show moderate Bayesian evidence (3.79) supporting the presence of methane, but the spectrum does not display any clearly identifiable methane absorption features. The retrieved methane abundance is ~2 orders of magnitude lower than that of solar composition. The methane-depleted atmosphere strongly rejects simple equilibrium chemistry forward models with solar metallicity and a C/O ratio and disfavors high metallicity (100 times) and a low C/O ratio (0.3). This calls for additional physical processes such as vertical mixing and photochemistry, which can remove methane from the atmosphere.2022ApJ...940L..35Fhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/940/L35CatalogResearchIsServedByTAP VizieR generic servicerelated-toVI/151 : Search for radio emission from giant exoplanets (Griessmeier, 2016)I/345 : Gaia DR2 (Gaia Collaboration, 2018)J/MNRAS/411/L46 : Exoplanet magnetic fields (Vidotto+, 2011)J/ApJ/726/52 : HAT-P-18 and HAT-P-19 follow-up (Hartman+, 2011)J/AJ/144/139 : HAT-P-39, HAT-P-40, and HAT-P-41 follow-up (Hartman+, 2012)J/A+A/552/A119 : Planet-star and moon-planet interaction (Saur+, 2013)J/ApJ/764/18 : Frequencies of giant exoplanets (Le Bihan+, 2013)J/ApJ/766/9 : GALEX observations of exoplanet host stars (Shkolnik, 2013)J/ApJ/771/107 : Spectroscopy of faint KOI stars (Everett+, 2013)J/ApJ/796/48 : Exoplanet targets with Palomar/TripleSpec (Zellem+, 2014)J/A+A/573/A90 : STAGGER-grid of 3D stellar models. IV. (Magic+, 2015)J/ApJ/831/64 : Mass-metallicities for giant planets (Thorngren+, 2016)J/ApJ/834/17 : Mass & rad of planets, moons, low mass stars (Chen+, 2017)J/MNRAS/468/3907 : HAT-P-18b wavelength binned light curves (Kirk+, 2017)J/ApJS/239/14 : Revised exoplanet radii from Gaia DR2 (Johns+, 2018)J/A+A/630/A135 : Beyond exoplanet mass-radius relations (Ulmer-Moll+, 2019)J/ApJ/874/L31 : Giant planet bulk & atm. metallicities (Thorngren+, 2019)J/ApJ/893/L29 : Hot Jupiter predicted period changes (Bouma+, 2020)J/AJ/159/41 : ~550 exoplanet data using a neural network (Tasker+, 2020)J/AJ/163/228 : TESS exoplanet Limb-darkening coefficients (Patel+, 2022)J/ApJS/258/40 : ExoClock project. II. Exoplanet ephemerides (Kokori+, 2022)J/ApJS/265/4 : ExoClock project. III. Exoplanet ephemerides (Kokori+, 2023)J/AJ/165/104 : Emergent sp. IR fluxes of 122 hot Jupiters (Deming+, 2023)J/AJ/165/264 : 130 Stellar and planetary parameters (Bennett+, 2023)J/ApJS/270/14 : Transit times of hot Jupiters from TESS (Wang+, 2024)J/AJ/167/1 : Transit depth variability with TESS (Wang+, 2024)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/940/L35https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/940/L35http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/940/L35https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/940/L35https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/940/L35http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/940/L35GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapInfrareddefaultJ/ApJ/940/L35/table1HAT-P-18b transmission spectrumlambda[0.6/2.83] Wavelength mid-pointumem.wlfloatDepth