Frédérique’s PhD project is to use direct imaging to detect exoplanet companions in very large orbits around the 200 youngest stars in the solar neighbourhood. They are looking for exoplanets with a mass of 1 to 10 times that of Jupiter and a semi-major axis of 100 to 5000 astronomical units (AU), orbiting stars less than 100 million years old.
The study will allow to determine the prevalence of companion planets with very wide separation around young stars, and to determine their mass and separation distributions, and thereby constrain their formation process. Most known exoplanets have been found with the radial velocity or transit methods, used to detect planets much closer to their stars, i.e. less than 5 AU and 1 AU, respectively. The direct imaging technique for finding more distant planets is promising, especially in the case of young stars. The exoplanets orbiting these young stars have just formed and still have a great deal of thermal energy resulting from their gravitational contraction. Once their formation is complete, giant planets cool rapidly and become progressively fainter.
For her PhD project, Frédérique will use high-contrast imaging techniques to eliminate the glare from the host star will not be required. On the other hand, since the planets sought have a mass as small as Jupiter, it is essential to have highly sensitive tools for detecting objects with low luminosity.
For her Master (2012-2014), Frédérique sought and characterized wide-separation binary systems with one late component (Recherche et caractérisation de systèmes binaires à grande séparation dont une des composantes est tardive). The idea was to study 29 candidate pairs of stars and to determine whether each pair forms a binary system. Characterizing these binary systems tells us more about their formation and that of stars in general. These systems, consisting of low-mass stars very distant from one another, have very weak gravitational bonds. They are also very interesting if the host star is a brown dwarf, since we know little about how they are formed.
Many low-mass and brown dwarf stars are formed through violent processes that should, in theory, separate pairs of stars with weak gravitational bonds. Studying this kind of system thus helps set limit conditions for binary systems that can form efficiently, so as to eventually develop a complete theory of star formation. In addition, clearly characterizing the primary star in these systems makes it possible to estimate their age, a task that is quite difficult by other means.
Fourteen new binary systems with separation of over 250 AU and with one of the components being a late-M or L-type dwarf were found thanks to this research. The presence of systems consisting of an M-type dwarf and a substellar companion separated by more than 250 AU among the candidates is very interesting, since very few systems of this kind have been discovered to date.
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