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Literature
Date: 2/4/2025

Arxiv: First unambiguous detection of ammonia in the atmosphere of a planetary mass companion with JWST/MIRI coronagraphs Published: 12/30/2024 9:02:29 PM Updated: 2/3/2025 5:01:08 PM


Paper abstract: The newly accessible mid-infrared (MIR) window offered by the James WebbSpace Telescope (JWST) for exoplanet imaging is expected to provide valuableinformation to characterize their atmospheres. In particular, coronagraphs onboard the JWST Mid-InfraRed instrument (MIRI) are capable of imaging thecoldest directly imaged giant planets at the wavelengths where they emit mostof their flux. The MIRI coronagraphs have been specially designed to detect theNH3 absorption around 10.5 microns, which has been predicted by atmosphericmodels. We aim to assess the presence of NH3 while refining the atmosphericparameters of one of the coldest companions detected by directly imaging GJ 504b. Its mass is still a matter of debate and depending on the host star ageestimate, the companion could either be placed in the brown dwarf regime or inthe young Jovian planet regime. We present an analysis of MIRI coronagraphicobservations of the GJ 504 system. We took advantage of previous observationsof reference stars to build a library of images and to perform a more efficientsubtraction of the stellar diffraction pattern. We detected the presence of NH3at 12.5 sigma in the atmosphere, in line with atmospheric model expectationsfor a planetary-mass object and observed in brown dwarfs within a similartemperature range. The best-fit model with Exo-REM provides updated values ofits atmospheric parameters, yielding a temperature of Teff = 512 K and radiusof R = 1.08 RJup. These observations demonstrate the capability of MIRIcoronagraphs to detect NH3 and to provide the first MIR observations of one ofthe coldest directly imaged companions. Overall, NH3 is a key molecule forcharacterizing the atmospheres of cold planets, offering valuable insights intotheir surface gravity. These observations provide valuable information forspectroscopic observations planned with JWST.