My research focusses on the detection of brown dwarfs and giant planets with direct imaging, a method that allows to see these objects directly instead of observing their effects on their host stars. I am especially interested in looking at known planetary systems and isolated brown dwarfs (not orbiting stars) as a global population. Studying these objects as a broad family can tell us a lot about their fundamental properties, how they formed and evolved, or what to expect from their atmospheres. The work I conduct aims at achieving a more complete overview of the properties and demographics of these substellar populations, and to bridge observations and theory using statistical methods.
CHECK OUT MY RECENT PROJECTS BELOW:
Giant Planets around Brown Dwarfs
Using the Hubble Space Telescope (HST), I discovered CFHTWIR-Oph 98 (Oph 98 for short), a curious starless binary system, consisting of two very low-mass objects located 450 light years away from Earth. The more massive component, Oph 98 A, is a young brown dwarf with a mass of 15 times that of Jupiter. It was found to host a giant planetary companion, Oph 98 B, only 8 times heavier than Jupiter, and separated by 200 times the Earth-Sun distance. This provides a rare example of two objects similar in many aspects to extra-solar giant planets, orbiting around each other with no parent star.
The young Oph 98 planetary-mass binary, with a wide 200-au separation (Fontanive et al. 2020)
Although Oph 98 A and B have masses, temperatures and atmospheres comparable to those of gas giant planets orbiting around young stars, they most likely formed like stars. The discovery of Oph 98 not only provides two new precious examples free-floating worlds analogous to giant exoplanets, but also proves that such extremely low-mass objects can have giant planetary companions, and that the processes that create binary stars operate on scaled-down versions all the way down to these planetary masses.
Brown Dwarf Multiplicity Statistics
Several theories exist to explain the existence of brown dwarfs floating freely in space without a host star, but it is still unclear whether some of them are born like stars or rather like planets. Population studies provide very valuable insight into formation histories, making them critical for differentiating between proposed formation and evolution scenarios.
About half of Sun-like stars are in binary systems, with two stars orbiting each other. Smaller stars are less commonly in multiple systems, are in tighter binaries and show a clear tendency towards equal-mass systems. Using the Hubble Space Telescope images, I demonstrated that the trends seen in the binary statistics of stars continue across the substellar regime, persisting down to the very lowest-mass brown dwarfs.
This observed continuity between the binary frequencies and population distributions of star and brown dwarf binaries suggests a common formation mechanism for the stellar and substellar regimes, providing crucial information to test formation models.
Decreasing binary fraction with stellar mass into the brown dwarf regime (Fontanive et al. 2018)
Target Selection for Imaging Programs with COPAINS
Comparing the predictions of the code to the measured or expected sensitivity from various imaging instruments, this in turn enables us to robustly select the most promising targets for direct imaging campaigns searching for low-mass companions. Such an informed selection method will help reduce the null detection rates from current pro-grams and will significantly increase the current census of wide brown dwarfs and planetary companions to stars.
The wobble of a star in its orbit induced by the gravitational pull of a companion is one of the most efficient ways to detect that companion. When the movement is in the plane of the sky, it can be visible as a change in the star’s apparent position. A nonlinear apparent motion may thus serve as evidence for the existence of an unseen companion.
COPAINS is new tool developed to identify previously undiscovered companions based on changes in stellar proper motions. This innovative procedure allows for dyna-mical predictions of the possible masses and separations of hidden companions compatible with observed astrometric trends, marginalised over unknown orbital elements.
The COPAINS target selection tool for direct imaging surveys based on proper motions
Massive Planets in Stellar Binaries
Stellar multiplicity is believed to influence planetary formation and migration, although the precise nature and extent of this role remain ambiguous. I conducted a survey aimed at testing the impact of binarity on the formation and/or evolution of the most massive, close-in giant planets and brown dwarfs, which are extremely challenging to explain with current theoretical models.
With this survey, I showed that stars hosting massive planets on very short separations are almost all part of multiple-star systems. These results demonstrates that binarity plays a crucial role in the existence of these planetary systems. This high binary rate is also larger than for lower-mass planets on similar orbits, suggesting that the influence from stellar companions only affect high-mass planets.
These results provide important information to better understand planet formation and im-prove theoretical simulations, but also help the design of observational surveys searching for new exoplanets and brown dwarf companions.
The very high binary fraction of stars hosting massive planets and brown dwarfs on close orbits (Fontanive et al. 2019)
Occurrences of directly-imaged exoplanets
The direct imaging method is the only way to detect a planet based on its own emitted light, rather than through the effect of the planet on its host star, but is only sensitive to very massive planets orbiting from very large distances. Constraining the demographics and architectures of giant exoplanets and brown dwarfs on wide orbits allows to test fingerprints of formation mechanisms, and provides rich sources of empirical constraints for planet formation and migration simulations.
Planets and brown dwarfs detected in the SHINE direct imaging survey (Vigan, Fontanive et al. 2020)
SHINE (SpHere INfrared survey for Exoplanets) is a large dedicated direct imaging survey using the high-contrast imager SPHERE at the Very Large Telescope (VLT), to perform a census of young giant exoplanets in the Solar neighbourhood.
I led the statistical analysis of the first 150 stars observed for the SHINE survey (Vigan, Fontanive et al. 2020).
Comparing observations to theore-tical models, we found that more massive stars produce more giant planets, and low-mass stars have more brown dwarf companions.