2020/05/05 by Joshua D. Lothringer, Guangwei Fu, David K. Sing +1 · 44 citations
Physics and Astronomy · #Astronomy and Astrophysical Research #Atmosphere (unit) #Exoplanet #Hot Jupiter #Planet #Rayleigh scattering #Scattering #Scientific Research and Discoveries #Spectral line #Stellar, planetary, and galactic studies #Transit (satellite) #astro-ph.EP
paper · pdf · doi:10.3847/2041-8213/aba265
published in The Astrophysical Journal Letters 898(1), L14 (IOP Publishing) · 9 pages, 5 figures. Submitted to ApJL
arxiv created 2020/05/05 · openalex created_date 2020/05/13 · openalex publication_date 2020/07/01 · arxiv updated 2020/07/29 · openalex updated_date 2026/08/05
Abstract The transmission spectra of ultra-hot Jupiters observed shortward of 0.5 μ m indicate strong absorption. Previous explanations have included scattering, photochemistry, escaping metals, and disequilibrium chemistry. In this Letter, we show that slopes and features shortward of 0.5 μ m can be caused by opacity not commonly considered in atmosphere models of exoplanets but guaranteed to be present if conditions are near chemical equilibrium including, but not limited to, atoms and ions of Fe, Ti, Ni, Ca, Cr, Mn, and SiO. Using the PHOENIX atmosphere model, we describe how the short-wavelength transit spectrum varies with equilibrium temperature between 1000 K and 4000 K, as well as the effect that the rainout of condensates has at these wavelengths. We define two spectral indices to quantify the strength of the NUV and blue absorption compared to that in the red-optical, finding that the NUV transit depth will significantly exceed the transit depth from Rayleigh scattering alone for all hot Jupiters down to around 1000 K. In the blue-optical, hot Jupiters warmer than 2000 K will have transit depths larger than that from Rayleigh scattering, but below 2000 K, Rayleigh scattering can dominate, if present. We further show that these spectral indices may be used to trace the effects of rainout. We then compare our simulated transit spectra to existing observations of WASP-12b, WASP-33b, WASP-76b, and WASP-121b. Further observation of exoplanets at these wavelengths should be prioritized in the coming years as the Hubble Space Telescope nears the end of its operational capability.