François-René Lachapelle

PhD student, Université de Montréal

François-René’s PhD thesis title is “Search for Exoplanets and Satellites in Extrasolar Systems by High Precision Timing of Known Transits”. In the past fifteen years, the photometric transit technique has allowed the science community to identify more than two-thirds of the exoplanets known to date. It also allows scientists to obtain spectroscopic data of the atmosphere of these objects, among which some may have habitable temperatures.

The new frontier in this domain would be to discover an exomoon. Such a discovery would help to understand the formation and dynamic evolution of planetary systems. Furthermore, the potential habitability of those worlds makes them prime candidates for exobiology.

The Mont-Mégantic Observatory will soon provide its 1.6 m telescope with a photometer, which is specially optimized for the detection of temporal variation in transit light curves of exoplanets; the PESTO camera (Planets Extra-Solar in Transit and Occultation). The main goal is to detect exomoons or multiple exoplanet systems by their dynamical effects on known planets. To do so, this instrument uses the photon-counting EMCCD detector technology, which allows for sensitive detections at high cadence while eliminating readout noise and delays between exposures. The readings obtained are time-stamped accurately to retrieve the transit chronology with an unprecedented precision. Technologies combined in this camera will give PESTO capabilities unmatched in the field.

The discovery of the first exomoon would obviously be a great success, but considering the sensitivity of the camera, a zero detection would also allow to constrain the presence of such systems. In addition, the transit timing technique can also probe for multiple planet systems in a range unavailable otherwise.

During his PhD, François-René will observe repeatedly a list of chosen targets in order to constrain their transit timing. Reduction and analysis tools for this new device will be elaborated. Results will then allow to statistically conclude on the population of exomoons, while also potentially bringing to light exoplanets and exomoons candidates.


François-René’s Master thesis (2011-2013) was to study substellar companions in the Upper Scorpius region. Recent observations of young stars using adaptive optics have led to the discovery of several companions of sub-stellar mass having orbital separations of several hundred astronomical units. Because of their great distance from the primary star, the formation of these bodies cannot be explained perfectly by standard models such as agglomeration and accretion, gravitational instabilities in the disk or the fragmentation of a protostellar cloud. It is possible that these companions were first formed at a smaller separation and, as a result of gravitational interactions between several planets, have migrated to their current position. This theory motivated further observations in order to seek other companions in these systems.

The project goal was to analyze the known companions of 4 systems as well as to search for other, closer companions. The proposed targets were young stars, which allow to observe bodies of sub-stellar mass with sufficient remaining brightness to be detected in the near infrared. In addition to photometry, their atmospheres can be analyzed spectroscopically.

Since evolution and atmosphere models are still uncertain for young sub-stellar objects (with low surface gravity), such observations are important for establishing calibrations. Analyzing angular differential imaging data also allowed to better constrain the presence of other companions.

The purpose of the detailed understanding of these systems is to impose some constraints on formation and evolution models of brown dwarfs and the evolution of their atmospheric composition. By comparing the companions’ spectra to model atmospheres, we can determine their temperature, chemical composition, etc. This allowed to study how well suited these models are to describe young brown dwarfs and planets.

Interpreting these results using current models of planetary system formation and evolution (accretion, gravitational instability, fragmentation of a collapsing cloud, interactions with other bodies, etc.) also brought better understanding of the origin of these systems and even the formation of planets and stars in general.


David Lafrenière


Office : Complexe des sciences, B-3435-2