Detection of Fe and evidence for TiO in the dayside emission spectrum of WASP-33b

Abstract

Context. Theoretical studies predict the presence of thermal inversions in the atmosphere of highly irradiated gas giant planets. Recent observations have identified these inversion layers. However, the role of different chemical species in their formation remains unclear. Aims. We search for the signature of the thermal inversion agents TiO and Fe in the dayside emission spectrum of the ultra-hot Jupiter WASP-33b. Methods. The spectra were obtained with CARMENES and HARPS-N, covering different wavelength ranges. Telluric and stellar absorption lines were removed with SYSREM. We cross-correlated the residual spectra with model spectra to retrieve the signals from the planetary atmosphere. Results. We find evidence for TiO at a significance of 4.9σ with CARMENES. The strength of the TiO signal drops close to the secondary eclipse. No TiO signal is found with HARPS-N. An injection-recovery test suggests that the TiO signal is below the detection level at the wavelengths covered by HARPS-N. The emission signature of Fe is detected with both instruments at significance levels of 5.7σ and 4.5σ, respectively. By combining all observations, we obtain a significance level of 7.3σ for Fe. We find the TiO signal at Kp = 248.0−2.5+2.0 km s−1, which is in disagreement with the Fe detection at Kp = 225.0−3.5+4.0 km s−1. The Kp value for Fe is in agreement with prior investigations. The model spectra require different temperature profiles for TiO and Fe to match the observations. We observe a broader line profile for Fe than for TiO. Conclusions. Our results confirm the existence of a temperature inversion layer in the planetary atmosphere. The observed Kp offset and different strengths of broadening in the line profiles suggest the existence of a TiO-depleted hot spot in the planetary atmosphere.

Magnetic Drag and 3D Effects in Theoretical High-resolution Emission Spectra of Ultrahot Jupiters: the Case of WASP-76b

“…Longer observations over large ranges of orbital phase should use multiple templates for best results and to avoid misleading retrieved net Doppler shifts. While here we find different velocity components due to the spatial variation in the planet's thermal structure, a similar effect resulting from the spatial variation in chemical abundances may have been seen in Cont et al (2021), who detected two atmospheric species with significant differences in associated velocities in the UHJ WASP-33b. They interpret this large velocity offset as a result of the depletion of TiO (but not Fe) near the substellar point, while both species exist on the terminator of the planet.…”

Confirmation of Iron Emission Lines and Non-detection of TiO on the Dayside of KELT-9b with MAROON-X

“…This is perhaps an indication that the species are distributed differently in the planet's atmospheres, thus contradicting our assumption of 1D geometry and/or constant abundances with altitude. A similar, but larger, velocity offset was recently seen between Fe and TiO in WASP-33b (which is a cooler planet than KELT-9b;Cont et al 2021). If such an inhomogeneity exists in KELT-9b's atmosphere then that could provide another explanation for our surprising retrieval results for the ionized species.…”

Magnetic Drag and 3-D Effects in Theoretical High-Resolution Emission Spectra of Ultrahot Jupiters: the Case of WASP-76b

“…Longer observations over large ranges of orbital phase should use multiple templates for best results and to avoid misleading retrieved net Doppler shifts. While here we find different velocity components due to spatial variation in the planet's thermal structure, a similar effect resulting from spatial variation in chemical abundances may have been seen in Cont et al (2021), who detected two atmospheric species with significant differences in associated velocities in the UHJ WASP-33b. They interpret this large velocity offset to be a result of depletion of TiO (but not Fe) near the substellar point while both species exist on the terminator of the planet.…”