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