CRIRES+ detection of CO emissions lines and temperature inversions on the 
dayside of WASP-18b and WASP-76b

Yan, F.; Nortmann, L.; Reiners, A.; Piskunov, N.; Hatzes, A.; Seemann, U.; Shulyak, D.; Lavail, A.; Rains, A. D.; Cont, D.; Rengel, M.; Lesjak, F.; Nagel, E.; Kochukhov, O.; Czesla, S.; Boldt-Christmas, L.; Heiter, U.; Smoker, J. V.; Rodler, F.; Bristow, P.; Dorn, R. J.; Jung, Y.; Marquart, T.; Stempels, E.

doi:10.1051/0004-6361/202245371

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CRIRES⁺ detection of CO emissions lines and temperature inversions on the dayside of WASP-18b and WASP-76b

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Rengel, M.
Planetary Science Department, Max Planck Institute for Solar System Research, Max Planck Society;

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https://ui.adsabs.harvard.edu/abs/2023A&A...672A.107Y
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Citation

Yan, F., Nortmann, L., Reiners, A., Piskunov, N., Hatzes, A., Seemann, U., et al. (2023). CRIRES⁺ detection of CO emissions lines and temperature inversions on the dayside of WASP-18b and WASP-76b. Astronomy and Astrophysics, 672, A107. doi:10.1051/0004-6361/202245371.

Cite as: https://hdl.handle.net/21.11116/0000-000D-8C72-5

Abstract

The dayside atmospheres of ultra-hot Jupiters (UHJs) are predicted to possess temperature inversion layers with extremely high temperatures at high altitudes. We observed the dayside thermal emission spectra of WASP-18b and WASP-76b with the new CRIRES⁺ high-resolution spectrograph at near-infrared wavelengths. Using the cross-correlation technique, we detected strong CO emission lines in both planets, which confirms the existence of temperature inversions on their dayside hemispheres. The two planets are the first UHJs orbiting F-type stars with CO emission lines detected; previous detections were mostly for UHJs orbiting A-type stars. Evidence of weak H₂O emission signals is also found for both planets. We further applied forward-model retrievals on the detected CO lines and retrieved the temperature-pressure profiles along with the CO volume mixing ratios. The retrieved logarithmic CO mixing ratio of WASP-18b (−2.2_−1.5^+1.4) is slightly higher than the value predicted by the self-consistent model assuming solar abundance. For WASP-76b, the retrieved CO mixing ratio (−3.6_−1.6^+1.8) is broadly consistent with the value of solar abundance. In addition, we included the equatorial rotation velocity (υ_eq) in the retrieval when analyzing the line profile broadening. The obtained υ_eq is 7.0 ± 2.9 km s⁻¹ for WASP-18b and 5.2_−3.0^+2.5 km s⁻¹ for WASP-76b, which are consistent with the tidally locked rotational velocities.