Possible Observational Criteria for Distinguishing Brown Dwarfs from Planets

The difference in formation process between binary stars and planetarysystems is reflected in their composition as well as their orbitalarchitecture, particularly orbital eccentricity as a function of orbitalperiod. It is suggested here that this difference can be used as anobservational criterion to distinguish between brown dwarfs and planets.Application of the orbital criterion suggests that with three possibleexceptions, all of the recently-discovered substellar companions discovered todate may be brown dwarfs and not planets. These criterion may be used as aguide for interpretation of the nature of sub-stellar mass companions to starsin the future.Comment: LaTeX, 11 pages including 2 figures, accepted for publication in the Astrophysical Journal Letter