Varley, RJ; (2016) Exoplanet Spectroscopy with Current and Future Instruments. Doctoral thesis , UCL (University College London).

Abstract

When I first started in this field the number of exoplanets discovered was around a thousand. That number is now threefold and tens of thousands more are expected to be discovered in the next decade. Exoplanets have become relatively easy to detect, but still remain difficult to understand. Part of this is due to our eagerness, we push the limits of current instrumentation whilst we develop and build the next generation. The lessons we learn here are vital for guiding what we do next, but the path is rocky and we must be careful. Detecting molecules in exoplanets through transit spectroscopy means measuring light from a star at a precision of one part in ten thousand. A challenge requiring sophisticated analysis techniques which can hinder as well as help. We must ask ourselves how we can be confident in what we have retrieved. The work I describe here and that which has occupied my life over the last few years is my attempt to bring confidence to the discussion. The instrument simulator Wayne was born of a desire to understand the Hubble Space Telescope's WFC3 Instrument --- particularly during the transit of an exoplanet. WFC3 exhibits many systematics and with minimal analysis produces planetary spectra best described as noise. The spectra reported in the literature are mixed, with many flat spectra being observed. Are these spectra truly flat or has the signal been removed in our analysis? With Wayne we can test our analysis pipelines on simulated data to see if they can recover the input signal, and use this result to improve their robustness. The second theme of this work is building the foundations to support the tidal wave of discoveries approaching us. We need an easy way to search through currently known exoplanets for optimal proposal targets, and be able to use the entire database when assessing the yield of new missions. The ExoData project was developed for this, and along with the instrument simulator for the EChO concept mission (EChOSim) I have used it to simulate the transit of hundreds of exoplanets. This work was designed to be repeated and adapted, and has already been re-purposed for the new mission concepts, TWINKLE and ARIEL. With these projects I have started the work to gain deeper insight into our instrumentation, the tools we use and the exoplanet population. I hope they help us move forward in ensuring our results are more reliable and repeatable.

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