Detection of Fe I Emission in the Dayside Spectrum of WASP-33b

Stevanus K. Nugroho, Neale P. Gibson, Ernst J. W. de Mooij, Miranda K. Herman, Chris A. Watson, Hajime Kawahara, Stephanie R. Merritt

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5 Citations (Scopus)


We analyze the high-resolution emission spectrum of WASP-33b taken using the High Dispersion Spectrograph (R ~ 165,000) on the 8.2 m Subaru telescope. The data cover λ ≍ 6170-8817 Å, divided over 30 spectral orders. The telluric and stellar lines are removed using a de-trending algorithm, SYSREM, before cross-correlating with planetary spectral templates. We calculate the templates assuming a 1D plane-parallel hydrostatic atmosphere including continuum opacity of bound-free H- and Rayleigh scattering by H2 with a range of constant abundances of Fe I. Using a likelihood-mapping analysis, we detect an Fe I emission signature at 6.4σ located at Kp of 226.0 _{-2.3}^{+2.1} km/s and vsys of -3.2 _{-1.8}^{+2.1} km/s — consistent with the planet's expected velocity in the literature. We also confirm the existence of a thermal inversion in the dayside of the planet, which is very likely to be caused by the presence of Fe I and previously detected TiO in the atmosphere. This makes WASP-33b one of the prime targets to study the relative contributions of both species to the energy budget of an ultra-hotJupiter. * Based on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.
Original languageEnglish
Article number L31
Number of pages9
JournalThe Astrophysical Journal Letters
Issue number2
Publication statusPublished - 28 Jul 2020


  • Exoplanet atmospheres
  • Exoplanet atmospheric composition
  • High resolution spectroscopy
  • 487
  • 2021
  • 2096

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