On Spectroscopic Phase-curve Retrievals: H2 Dissociation and Thermal Inversion in the Atmosphere of the Ultrahot Jupiter WASP-103 b

Abstract

Abstract This work presents a reanalysis of the spectroscopic phase-curve observations of the ultrahot Jupiter WASP-103 b obtained by the Hubble Space Telescope (HST) and the Spitzer Telescope. Traditional 1D and unified 1.5D spectral retrieval techniques are employed, allowing to map the thermal structure and the abundances of trace gases in this planet as a function of longitude. On the dayside, the atmosphere is found to have a strong thermal inversion, with indications of thermal dissociation traced by continuum H− opacity. Water vapor is found across the entire atmosphere but with depleted abundances of around 10−5, consistent with the thermal dissociation of this molecule. Regarding metal oxide and hydrides, FeH is detected on the hot spot and the dayside of WASP-103 b, but TiO and VO are not present in detectable quantities. Carbon-bearing species such as CO and CH4 are also found, but since their detection is reliant on the combination of HST and Spizer, the retrieved abundances should be interpreted with caution. Free and Equilibrium chemistry retrievals are overall consistent, allowing to recover robust constraints on the metallicity and C/O ratio for this planet. The analyzed phase-curve data indicates that the atmosphere of WASP-103 b is consistent with solar elemental ratios.