Étude de variabilité photométrique infrarouge de naines brunes
Brown dwarfs are astronomical objects of low mass ( 0.012 - 0.075 M_Sun  ) and low temperature ( T < 3,500 K ).  While they do form like stars through gravitational collapse of a molecular gas cloud, they do not have sufficient mass to sustain nuclear fusion reactions in their core. Relatively hot brown dwarfs (type L) are covered by an homogeneous dust cloud cover that progressively disappears from their atmosphere when the temperature falls below 1,500 K (type T).  Therefore, brown dwarfs near the L/T transition should be partially covered with clouds. Due to the fast rotation of brown dwarfs (2 h - 12 h), this inhomogeneous cloud cover should produce photometric variability observable in the J band (1.2 um), the wavelength at which the clouds have the strongest opacity.  This thesis presents the results of a search for infrared photometric variability in brown dwarfs near the L/T transition. The observations, obtained at the Observatoire du Mont-Mégantic, have allowed the photometric follow-up of nine targets in the J band.  Only one of them, SDSS J105213.51+442255.7 (T0.5), showed periodic variations with a period of about 3 hours with a peak-to-peak amplitude ranging from 40 to 80 mmag.  For the remaining eight targets, we can place upper limits (3 sigma) of 15 mmag for the amplitude of periodic variability over a period range betwen 1 and 6 hours.  While these results support the hypothesis that partial dust cloud covers do exist among L/T dwarfs, this phenomenon is by no means ubiquitous.
CPAPIR Brown dwarfs Variability Photometry Infrared CPAPIR