Detection of Fe\, i Emission in the Day-side Spectrum of WASP-33b
Abstract
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\,, 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 1-D 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 6.4-σ located at Kp of 226.0\,+2.1-2.3\,km\,s-1and vsys of -3.2\,+2.1-1.8\,km\,s-1 -- consistent with the planet's expected velocity in the literature. We also confirm the existence of a thermal inversion in the day-side 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-hot Jupiter.