Anne Boucher, an iREx student at the Université de Montréal, submitted her doctoral thesis at the end of 2021. She summarises the research project she carried out as part of her Ph.D here.
During my Ph.D, I became interested in the atmosphere of gas giant exoplanets that orbit very close to their star. Thanks to a technique called transmission spectroscopy, I studied the chemical composition of their atmosphere, which gives a lot of information on their formation and evolution mechanisms. The detailed study of these exoplanets, which we sometimes call hot Jupiters or hot sub-Saturns, provides a better understanding of the physical, chemical, and dynamical processes that govern the atmosphere of these celestial objects.
I mainly used data from the SPIRou instrument, a high-resolution spectropolarimeter that operates in the near infrared and is installed at the Canada-France-Hawaii Telescope. We first observed HD 189733 b, one of the most studied exoplanets, to build the analysis codes. By exploiting transit spectroscopy, we were able to confirm the presence of water and determine its abundance. The results obtained, consistent with previous studies, indicate that the atmosphere of HD 189733 b is relatively clear (free of clouds) and that the planet likely formed far from its star, where it is cold enough to find water in the form of ice. A strong blueshift of water absorption was observed, which could be a consequence of the presence of strong winds in the atmosphere.
Artistic representation of the exoplanet HD 189733 b, credit : NASA, ESA, and G. Bacon (STScI)
Next, we studied WASP-127 b, a less massive exoplanet, but much larger than Saturn. A recent study of data from the Hubble Space Telescope (HST) and the Spitzer Space Telescope could not differentiate between two atmospheric scenarios: a low carbon-to-oxygen (C/O) ratio with little carbon monoxide (CO), or a high ratio with a lot of CO. As this ratio helps to determine how a planet was formed, we decided to use SPIRou, which makes it possible to observe a band of CO not observable with HST and Spitzer. We were able to determine that there was very little CO and a very low C/O, which has rarely been observed, but which is supported by some more realistic training scenarios that vary over time. The SPIRou data also confirmed the presence of water and suggests that, if confirmed, there could even be hydroxyl (OH): an unexpected detection since the exoplanet is so cold.
This work has allowed to develop the expertise of the Université de Montréal in high resolution near-infrared transit spectroscopy, in particular with SPIRou, allowing to explore the atmospheric conditions of hot Jupiters and sub-Saturns. This first joint analysis made on high and low resolution transmission data allowed to obtain better constraints on the atmospheric parameters. This method is proving to be a very powerful tool for the study of atmospheres and will be even more so with the revolutionary capabilities of JWST.
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Anne worked on her Ph.D. at the Université de Montréal between 2016 and 2022, under the supervision of David Lafrenière. Her thesis will soon be available.
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