Fig. 1: Dayside thermal emission spectrum of WASP-18b.
From: A broadband thermal emission spectrum of the ultra-hot Jupiter WASP-18b
a, Observed dayside planet-to-star flux ratio spectrum (black points) and their 1σ error bars, binned at a fixed resolving power of R = 50 for visual clarity. Past HST7 (red points), TESS (see Methods) and Spitzer15 (grey points) are shown for comparison. We show the best-fit model (blue line) from the SCARLET chemical-equilibrium retrieval, extrapolated to the TESS and Spitzer wavelengths considering the same atmospheric parameters. We find that the measured spectrum is in good agreement with the past HST observations. The throughput-integrated model is shown for the TESS and Spitzer points (blue points). The white (broadband) light curve (white points) and three example spectrophotometric light curves (blue, green and orange points at 1.05, 1.72 and 2.77 μm, respectively), along with their best-fitting models (black line), are shown to scale. The phase variation of the measured planetary flux around the secondary eclipse is clearly visible. b, Planetary thermal emission spectrum of WASP-18b, as computed from the Fp/Fs spectrum and the PHOENIX stellar spectrum. The shortest wavelengths of the NIRISS/SOSS first order reach the maximum of the planetary spectral energy distribution, thereby enclosing 65% of the total thermal energy emitted by the planet. Blackbody spectra for temperatures T = 2,850 K (dotted line), 2,950 K (dash-dotted line) and 3,050 K (dashed line) are shown in purple, with the best-fitting blackbody spectrum to the NIRISS data being T = 2,950 ± 3 K.
