Frédéric Genest

2017 Trottier iREx Summer Intern and B.Sc. student, McGill University

Frédéric is currently doing a dual degree at McGill University in Mathematics and Physics (Honours).

During the summer of 2017, with David Lafrenière, he studied the atmosphere of exoplanets around low-mass and low-temperature stars (M dwarfs). He also studied the effect that water vapour in a star’s atmosphere has on an exoplanet’s spectrum obtained by transit spectroscopy. The objective being to be able to disentangle the water in the star’s atmosphere from that in the exoplanet’s atmosphere.


David Lafrenière

Interview with Frédéric on his 2017 internship (translated from French)
What was the topic of your internship?

M starts are great targets to observe and characterize Earth-size exoplanets, since the low luminosity and small size of these stars make the transits of planets much easier to measure. However, these stars are cold enough to contain water in their atmosphere and their startspots contain a little more of it, being colder. When a planet transit in front of an M star without occulting any starspot, there is a water absorption feature that appears that can be mistaken for the detection of water in the atmosphere of the planet. My project’s goal was to determine if we can identify the origin of the water absorption feature (from the starspots or from the planet’s atmosphere) using the fact that the planet has a varying radial velocity due to its orbital motion around the star. We were hoping this variation would cause a shift of the absorption feature (Doppler effect) that can be detected using high resolution spectroscopy (with SPIRou, for example).

What is interesting about it?

The scientific community is really interested in M stars right now, because they are good targets to find earth-like planets that we will be able to characterize in a near future. This project was meant to pave the way for the analysis that will be made with new instruments that will allow these discoveries. What made the project interesting to me was that it addressed a problem that was, to my knowledge, not studied thoroughly before, but that will probably have an important effect for the search of exoplanets.

What did you discovered? What is your most important result?

I have obtained two interesting results. The first one is that it will be possible to distinguish water in the atmosphere of the star from that in the atmosphere of a planet. The variation of the radial velocity of the planet will induce a shift that will be measurable with SPIRou. However, it will be necessary to compare the observations with models that are extracted from thousands of different atmospheres. The second result, just as important, is that depending on the atmosphere of the planet, it will sometimes be possible to conclude on the presence of water in it without using any complex analysis method.

What did you learn this summer?

I have learned a lot! I had to learn about transit spectroscopy and exoplanet’s atmospheres. I also learned to code much better (in Python) and to build and use various models. I learned about M stars and their properties. I also learned a lot of general knowledge in astronomy.

What was the biggest challenge during your internship?

The beginning of the project, when I had to learn how to code and the various astrophysical knowledge I needed during the summer. It can be challenging to read many scientific papers to know how the project will be carried out. Fortunately, this period didn’t last long and I was soon able to code simple models and put to practice the knowledge I acquired.

What did you like the most about your internship?

I liked the feeling to be working on a useful, relevant and interesting project. I really liked the work atmosphere: I was quite autonomous, and I never felt too stressed. It was also a pleasure to work with the other interns.