My thesis in 400 words: Anne Boucher


Anne Boucher, iREx student at the University of Montreal, presented her doctoral thesis in the spring of 2022. Here she summarizes the research project she carried out in the context of her doctorate.

IMG_5577During 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 provides a lot of information on their formation and evolution mechanisms. Detailed study of these exoplanets, which are sometimes called hot Jupiters or hot sub-Saturns, allows for a better understanding of the physical, chemical and dynamic processes that govern the atmosphere of these astronomical objects.

These are the data from the SPIRou instrument, a high resolution spectropolarimeter that operates in the near infrared and 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. Using 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 (cloudless) 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 in water absorption was observed, which could be a consequence of strong winds in the atmosphere.

Artist’s impression of the exoplanet HD 189733 b, credit: NASA, ESA and G. Bacon (STScI)

AndNext, we studied WASP-127 b, a less massive but much larger exoplanet than Saturn. A recent study using data from the Hubble Space Telescopes (HST) and the Spitzer was unable to distinguish between two atmospheric scenarios: a low carbon / oxygen (C / O) ratio with low carbon monoxide (CO) or a strong relationship with a lot of CO. As this report helps determine how a planet formed, we decided to use SPIRou, because this tool allows us to observe a CO band that is not accessible to HST and Spitzer. Using this data, it was determined that there was very little CO and very low CO, which was rarely seen, but is supported by some more realistic time-varying training scenarios. The SPIRou data also confirmed the presence of water and shows a signal consistent 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.

This work has allowed us to develop our experience in high resolution near infrared transit spectroscopy at the University of Montreal, in particular with SPIRou, thus making it possible to explore the atmospheric conditions of hot Jupiter and sub-Saturn. This first joint analysis carried out on high and low resolution transmission data allowed to obtain better constraints on 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 received her doctorate from the University of Montreal between 2016 and 2022, under the supervision of David Lafrenière. Her thesis will be available soon.


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