My thesis in 400 words: Anne Boucher

Anne Boucheran iREx student at the Université de Montréal, submitted her doctoral thesis in the spring of 2022. Here she summarizes the research project she carried out as part of her doctorate.

During my PhD, 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 are sometimes called hot Jupiters or hot sub-Saturns, allows a better understanding of the physical, chemical and dynamic processes that govern the atmosphere of these astronomical objects.

This is the instrument data SPIrou, a high-resolution near-infrared spectropolarimeter installed at the Canada-France-Hawaii telescope, which I mainly used. 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 (without clouds) and that the planet would have formed far from its star, where it is cold enough to find water in the form of ice. A strong blue shift 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)

ENext, we studied WASP-127 b, a less massive exoplanet, but much larger than Saturn. A recent study that used data from the Hubble Space Telescopes (HST) and Spitzer could not differentiate between two atmospheric scenarios: a low carbon-to-oxygen (C/O) ratio with low carbon monoxide (CO), or a strong report with a lot of CO. As this report helps to determine how a planet formed, we decided to use SPIRou, because this instrument allows to observe a band of CO not accessible to HST and Spitzer. Using this data, it was determined that there was very little CO and very low C/O, which has rarely been observed, but is supported by some more realistic time-varying formation scenarios. The SPIRou data also confirmed the presence of water and shows a consistent signal with hydroxyl (OH), which needs to be reconfirmed because the exoplanet is too cold to easily explain this result. The SPIRou data also confirmed the presence of water and suggests a possible detection of hydroxyl (OH), an unexpected detection since the exoplanet is too cold.

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This work has made it possible to develop our expertise in high-resolution transit spectroscopy in the near infrared at the University of Montreal, in particular with SPIRou, thus making it possible to explore the atmospheric conditions of hot Jupiters and sub-Saturns. This first joint analysis made on high and low resolution data in transmission allowed to obtain better constraints on the atmospheric parameters. This method is proving to be a very powerful tool for studying atmospheres and will be even more so with the revolutionary capabilities of the James Webb Space Telescope.

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Anne did his doctorate at the University of Montreal between 2016 and 2022, under the supervision of David Lafreniere. His thesis will be available shortly.

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