High resolution Doppler spectroscopy of a transiting ultra-hot Jupiter at optical wavelengths

Until recently, this was a wavelength regime little-explored in hot Jupiter atmospheres using cross-correlation techniques. Using the Doppler spectroscopy method, which takes advantage of the high radial velocity of the planet to disentangle its spectral lines from those of its host star, two investigations were performed.<br><br>The first study comprises a comprehensive search for the molecules TiO and VO, strong optical absorbers previously theorised to drive thermal inversions in hot Jupiters.

No signs of either molecule could be found, though confirmation of the absence of VO awaits a more accurate linelist. These constraints provide evidence for recent theory, suggesting that TiO and VO are thermally dissociated in UHJs, and that the previously-observed thermal inversion in WASP-121b may be driven by atomic metals.<br><br>The second study presents the results of a broad search for neutral and ionised atomic species in the same dataset.

Forty-three species were searched for over a grid of varying temperatures and cloud-deck pressures. Twenty potential signals were flagged and investigated in detail, with seven of these classified as detections after applying a set of detection criteria assessing different aspects of the signals in detail. This study underlines the huge potential in studying UHJs at optical wavelengths and high-resolution.

In the future, these techniques will be applicable to observations from the next generation of high-resolution spectrographs, and may one day be used to characterise habitable planets.