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Carbon Monoxide Emission Lines In Jupiter's Ultrahot Atmosphere Indicate A Thermal Inversion Layer

For the first time, carbon monoxide emission lines with high spectral resolution were found for the first time in an exoplanet's infrared thermal spectrum on a daytime basis.

Alexander McCaslin
May 30, 2023332 Shares82956 Views
For the first time, carbon monoxide emission lineswith high spectral resolution were found in an exoplanet's infrared thermal spectrum daytime. These emission lines, discovered in the ultra-hot JupiterWASP-33b atmosphere, are unmistakable indications of its thermal inversion layer. These findings were reported by a team of researchers led by Lennart van Sluijs and Jayne L. Birkby from the University of Oxford, United Kingdom.
Ultra hot Jupiters offer a once-in-a-lifetime chance to study gaseous planets in a highly radioactive environment and learn about their chemistry and global atmospheric circulation. Their high daytime temperatures, which exceed 2200K, offer a new window for directly detecting volatile species in their vapour phase. Because of their tidally locked rotation and extreme day-to-night temperature contrast, global circulation models (GCMs) predict strong global jets and hot spots, which, combined with their relatively high star-to-planet contrast ratio, make them ideal targets for atmospheric characterisation using current observing facilities. A well-studied, very hot Jupiter is a well-known hot Jupiter whose atmosphere models predict a thermal inversion. This planet orbits an A5 star every 1.22 days.

Carbon Monoxide Absorption Spectrum

The researchers gave the first high-resolution spectroscopic measurements from the ARIES NIR spectrograph behind the MMT targeting WASP-33b. They created a public ARIES preprocessing pipeline to extract a spectral time series from raw detector pictures. This study employed various atmospheric modelling programmes to investigate the structure, chemistry, and dynamics of WASP33b's atmosphere. To begin with, identify absorption and emission characteristics. The model with the highest detection is a PHOENIX model adjusted to incorporate all opacity sources. The improved PHOENIX models enable investigation of the structure and chemical species of WASP-33b's atmosphere. The self-consistent assessment evaluates its efficiency, redistribution efficiency, and metallicity.
They detected CO by doing a cross-correlation analysis with PHOENIX model atmospheres using spectra from the MMT Exoplanet Atmosphere Survey, including pre-and post-eclipse orbital periods. They found that spectral line depths change with phase as measured by the scaling parameter and degree: the contrast between lines is greater after the eclipse. This is a common misunderstanding.

Hot Spot And Atmospheric Dynamics

The researchers employed the SPARC/MITgcm general circulation model, which was post-processed using the 3D gCMCRT radiative transfer tool, and interpreted the variance caused by an eastward-shifted hot spot. When the hot point faces Earth before the eclipse, the thermal profiles are shallower, resulting in a reduced line depth despite higher total flux. Following the eclipse, the western section of the day-side faces Earth, where the thermal profiles are significantly steeper, resulting in greater line depth despite lower overall flux. We show that even spectra with shallow resolution may be used to grasp the 3D character of close-in exoplanets when analysed using the log-likelihood framework. That resolution can be sacrificed for photon collecting power when the induced Doppler shift is strong enough. We stress that CO in extremely hot Jupiters is an excellent probe of their thermal structure and associated dynamics. Many atomic species that live in hot hosts like iron aren't affected by stellar activity, which isn't the case with this one.
Jupiter's thermal structure is asymmetric, with the hottest point shifting away from the substellar point. The great majority of observations and simulations show a movement of the hot spot towards the direction of the planet's rotation, which is commonly described as eastward. An eastward hot spot causes a hotter continuum and, consequently, more overall brightness during the pre-eclipse phases. Doppler shifts of 1-3 km/s are projected when the hot zone spins in and out of view while circling its host star.


This study's preliminary results are as follows:
  • HRCCS detects carbon monoxideemission lines for the first time in an extraterrestrial atmosphere. Carbon monoxide emission lines in WASP-33 b's atmosphere prove an inverted profile.
  • The best PHOENIX atmospheric models prefer a day-only heat redistribution.
  • The modified structure PHOENIX models demonstrate we are sensitive to the inversion layer temperature gradient but not to the lower atmospheric absolute temperatures.
  • The planet spectral line contrast is stronger soon after secondary eclipse than before, as seen by the mapping. P-T profiles from a GCM with an eastward offset hot spot explain the majority of phase-dependence in log(a). An offset hot spot causes an extra Doppler shift in mapping, which can show the longitudinal phase-dependent thermal structure of the atmosphere.
  • Unlike prior optical detections of atomic emission lines, no indication of stellar pulsations impacting the identification of carbon monoxide was found. At pressures seen, carbon monoxide provides an advantageous and excellent probe of the ultra hot Jultra hot thermal atmospheric structure probe
  • A substantial Doppler-shift generated by the exoplanet's orbital motion is used to isolate its spectra from its home star and telluric. The associated orbital Doppler shift is sufficient to displace the planet spectrum over many pixels, as predicted for close-in terrestrial lava planets and ultra-hot Jupiters.
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