Posted on July 5, 2022 by Érika Le Bourdais
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Anne Boucher, an iREx student at the University of Montreal, presented her PhD thesis at the end of 2021. Here it summarizes the research project she carried out as part of her Ph.D.
During my PhD I became interested in the atmospheres of gas giant exoplanets (as big as Jupiter or Saturn) that orbit very close to their star. Thanks to a technique called transmission spectroscopy, I studied the chemical composition of their atmospheres, which gives a lot of information about the mechanisms of their formation and evolution. The detailed study of these exoplanets, which we sometimes call hot Jupiters or hot Saturns, provides a better understanding of the physical, chemical and dynamical processes that govern the atmospheres of these astronomical objects.
I primarily used data from the SPIRou instrument, a high-resolution spectropolarimeter that operates in the near-infrared region and is installed on the Canada-France-Hawaii telescope. We first observed HD189733b, 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, consistent with previous studies, show that the atmosphere of HD 189733 b is relatively clean (no 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 is observed, a consequence of the dynamics and winds present in the atmosphere.
Artist rendering of the exoplanet HD 189733 b, credit: NASA, ESA and G. Bacon (STScI)
Next, we studied WASP-127b, a less massive exoplanet but much larger than Saturn. A recent study of data from the Hubble Space Telescope (HST) and Spitzer could not distinguish between two atmospheric scenarios: a low carbon-to-oxygen (C/O) ratio with little carbon monoxide (CO) or a high ratio and lots of CO (this ratio can to be related to the different learning scenarios). SPIRou, which makes it possible to observe a band of CO inaccessible to HST and Spitzer, was able to determine that there is very little CO and very low C/O, which is rarely observed but which is supported by some other realistic training scenarios, which vary over time. The SPIRou data also confirmed the presence of water and suggest that if confirmed, it may even have hydroxyl (OH), an unexpected finding because the exoplanet is so cold. I have shown that joint analysis of SPIRou and space telescope data allows for better constraints on atmospheric parameters.
This work has shown that high-resolution near-infrared transit spectroscopy, especially with SPIRou, is useful for studying the atmospheric conditions of hot Jupiters and sub-Saturns. In addition, the combination of low- and high-resolution data is a very powerful tool for studying the atmosphere and will be even stronger with JWST’s revolutionary capabilities.
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Ann is working on her Ph.D. degree at the Université de Montréal between 2016 and 2022 under the supervision of David Lafrenière. Her thesis will be available soon.
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