In section 10. Planets and planetary systems
Precise radial velocities of giant stars. XI. Two brown dwarfs in 6:1 mean motion resonance around the K giant star nu Ophiuchi
The K giant star nu_Oph has been known to harbor two brown dwarfs with periods of ~3170 and 530 days, that is, with a period ratio close to 6:1.
Quirrenbach et al. present a detailed analysis of over ten years' RV measurements, applying a self-consistent N-body model to determine the companion dynamical masses. They demonstrate that the two objects have minimum masses m sin i of ~22 and 25 Jupiter masses, and that they are indeed locked in a 6:1 mean motion resonance (MMR) that is stable over periods of million of years, forming the first known "super-planet" resonant system. Most likely, the two brown dwarfs formed in the way that planets form in the circumstellar disk, and underwent migration capture in MMR, although the precise formation mechanism (gravitational instability or core accretion) cannot yet be established.