Revealing the nature of brown dwarfs from population studies

(Pinfield, Burningham, Lucas, Jones)

We are leaders in the exploitation of new generation infrared sky surveys for brown dwarf discovery and study. Together UKIDSS, VISTA and WISE are providing an unprecedented view of the infrared sky which is probing a large volume of new parametre-space and revealing free-floating objects with masses and temperatures all the way into the planetary regime, and ages as old as the Galaxy itself.

• In recent years we doubled the number of known T dwarfs (Teff<1500K) through our follow-up and spectroscopic confirmation programmes. We identified the coolest T dwarfs in the Teff range down to 500K, and have ongoing parallax programmes to determine their luminosities.
• We were the first to identify an unexpected dearth in mid to late T dwarf numbers (compared to expectations from open cluster populations), that is either high-lighting problems with the latest evolutionary models or resulting from a varying initial mass function. Our ongoing studies are target this open question.
• We are carrying out a spectroscopic study of a major magnitude limited sample of UKIDSS L to mid T dwarfs to constrain the sub-stellar formation history of the Galaxy. This programme has to-date been awarded 20 nights of XShooter time on ESO's VLT.
• Our infrared proper motion catalogue combined with radial velocity measurements is revealing the kinematics of brown dwarf populations, giving important clues to their origin. We have recently identified the first T dwarfs with halo kinematics.
• The multiplicity of brown dwarfs is also crucial for revealing sub-stellar formation mechanisms. We study such multiplicity over a range of separations, using spectroscopy, high resolution imaging, and proper motion measurements.
• And we study brown dwarf atmospheric weather phenomena through photometric and spectroscopic monitoring.