POSSIBLE OBSERVATIONAL CRITERIA FOR DISTINGUISHING BROWN DWARFS FROM PLANETS

The difference in formation process between binary stars and planetary systems is reflected in their composition, as well as orbital archite cture, particularly in their orbital eccentricity as a function of orb ital period. It is suggested here that this difference can be used as an observational criterion to distinguish between brown dwarfs and pla nets. Application of the orbital criterion suggests that, with three p ossible exceptions, all of the recently discovered substellar companio ns may be brown dwarfs and not planets. These criterion may be used as a guide for interpretation of the nature of substellar-mass companion s to stars in the future.