Leave a comment

Anne Boucher, an iREx student at the University of Montreal, submitted her PhD thesis at the end of 2021. She summarizes here the research work she carried out as part of her PhD. During my PhD, I became interested in the atmosphere 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. It is the data from the SPIRou instrument, a high-resolution near-infrared spectropolarimeter installed on the Canada-France-Hawaii telescope, that I used primarily. We first observed HD189733b, one of the most studied exoplanets, to generate the analysis codes. Utilizing transmission spectroscopy, we were able to confirm the presence of water and determine its abundance. The results obtained, 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 was observed, a consequence of the dynamics and winds present in the atmosphere. Artist’s 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 differentiate 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 be linked to the various training scenarios). SPIRou, which makes it possible to observe a band of CO inaccessible to HST and Spitzer, was able to determine that there was very little CO and very low C/O, which has rarely been observed but is supported by some other realistic training scenarios that vary over time. The SPIRou data also confirmed the presence of water and suggest that, if confirmed, even hydroxyl (OH) could be present, an unexpected detection since the exoplanet is very cold. I showed that joint analysis of SPIRou data and these space telescopes allows for better constraints on atmospheric parameters. This work has demonstrated that high-resolution near-infrared transit spectroscopy, particularly with SPIRou, is useful for exploring the atmospheric conditions of hot Jupiters and subcorans. In addition, the combination of low and high resolution data is a very powerful tool for studying the atmosphere and will be even more so with JWST’s revolutionary capabilities. More information Anne worked 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.

← Countdown to Webb’s First Images