Characterising exoplanet atmospheres using high dispersion spectra

For the last few years most common way to measure a spectrum of an exoplanets is to make a differential measurement, observing a transit (when the planet passes in front of a star) or eclipse (when the planet passes behind the star) in multiple bands, or with a low-dispersion spectrograph. An alternative approach is to use high dispersion spectroscopy, resolving individual lines in the planet's spectrum, and exploiting the orbital motion of the planet around its orbit, which shifts the planet's spectrum relative to that of the star and to the Earth's atmosphere's transmission spectrum. This method can be applied to transiting and non-transiting planets, can allow the measurement of the planet's rotation rate and even of winds in its atmosphere, and may be used in the next decade to search for biosignature molecules in the atmospheres of habitable planets orbiting low-mass stars (using extremely large, ground-based telescopes). However, the results are critically sensitive to the correction of the stellar and telluric signals. The residual spectrum is the cross-correlated with a theoretical template, which enable a detection of individual molecules but not abundance measurements. Prof Aigrain has recently developed an alternative methodology to analyse this kind of datasets, which involves modelling the star, telluric and planet signals directly, using Gaussian Process regression to model the (unknown) planet spectrum. The student will develop and apply this method to existing archival near-infrared spectra and, during the course of the PhD, to new data from (e.g.) the refurbished CRIRES+ instrument on the VLT.
This project is aligned with STFC's key challenge B: How do stars and planetary systems develop and how do they support the existence of life. It will use data from STFC-supported facilities, in particular VLT/CRIRES. The work will be done in collaboration with Dr Matteo Brogi at the University of Warwick and Prof Jayne Birkby at the University of Amsterdam.