Modelling the 3D high-resolution spectra of hot Jupiters

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In the past ten years high resolution spectrum of exoplanet atmospheres became available from large ground based telescopes. Instruments such as NIRSPEC at the Keck telescope Hawaii or CRIRES at the Very Large Telescope Chile have been able to resolve individual spectral lines of both atoms such as sodium and molecules such as water and carbon monoxide. These observations not only allowed the detection and quantification of molecules but have provided the first direct measurement of an exoplanet atmospheric wind speed. With more than ten new instruments about to come to the sky in large telescope worldwide among them ESPRESSO at the Very Large Telescope and CARMENES at the Calar Alto have begun observing SPIRou at the Canada France Hawaii Telescope should start soon, high resolution spectra of exoplanet will be measured routinely with a high accuracy. Further ahead high resolution instruments such as METIS on the European Extremely Large Telescope will become our best chance to detect biosignatures in other worlds. Despite these exciting prospects, very small work has been done to interpret these observations. We learned from low resolution spectroscopywith space based telescopes such as Hubble or Spitzer or soon the James Webb Space Telescope that exoplanetary atmospheres are complex objects, particularly Hot Jupiters, the main targets of current observations. These planets have the size of Jupiter but orbit much close to their star than mercury. They are tidally locked, with a dayside heated to several thousands of degrees while their nightside never sees the star. Strong often supersonic winds transfer energy from the dayside to the nightside. Whereas the dayside can be hot enough to break molecules apart, the nightside shows signs of clouds made of rocky material such as silicates. High resolution spectroscopy observations are currently interpreted using one-dimensional atmospheric models. Whereas these can be used to atmospheric wind speeds and abundances from current observations they can be biased towards the wrong results. New more precise information such as recent ones by the ESPRESSO instrument can resolve the planetary limb during a transit, showing clear signs of 3D asymetries. For this project we will use a state of the art 3 dimensional global circulation model of hot exoplanets (the SPARC/MITgcm) to investigate the effects of a 3D thermal and wind structure on high-resolution observations. The dynamical model can predict complex thermal and chemical structure, cloud spatial distribution and wind patterns for a wide range of exoplanets. These outputs will be used by MCRT, a state of the art 3D monte carol radiative transfer code to calculate with a high precision the shape and position of the molecular lines observed with high resolution spectrocscopy. The student will determine the observational consequences of varying planetary parameters, such as equilibrium temperature, wind drag, gravity, cloud composition and re interpret current observations. We will also investigate what best 3D line shapes parametrization should be used when retrieving wind speed and abundances from the observations which should greatly enhanced the detectability of atmospheric species in these planets. Observation proposals in collaboration with local Oxford observes (such as Suzanne Aigrain in the astronomy departement) will be written to obtain open time on major observatories around the world following the insights gained from the modelling work