Session 3: Stellar Astrophysics

Title: Brown dwarfs and isolated planetary-mass objects in star clusters
Author: Rafael Rebolo    Main Session Speaker 

  Brown dwarfs are objects unable to sustain hydrogen burning in their interiors. Deep surveys and large scale infrared surveys have identified  a few hundred candidates free-floating  in star  clusters and in the solar neighborhood. 
  Several brown dwarf companions to low-mass stars have also been detected. In the absence of a direct mass determination, brown dwarfs can be identified by the presence of lithium and/or methane bands in their spectra. Our recent surveys in Orion show that brown dwarfs can form with any mass in the range between the minimum mass for hydrogen burning  (~75 M_Jupiter, at solar metallicity) and the minimum mass for deuterium burning (~13 M_Jup). Objects with  planetary masses, just 5-10 times that of Jupiter have also been detected free floating in very young star clusters.  Older and much cooler counterparts are likely to populate the solar neighborhood. We discuss  the  mass function in the brown dwarf domain  and its possible extension to masses in the planetary domain. If current estimates from young star forming regions are representative of the substellar population in the disk of our Galaxy, brown dwarfs and isolated Jupiter-like objects may outnumber stars