SECULAR RESONANCES AND COMETARY ORBITS IN THE BETA-PICTORIS SYSTEM

THE dusty disk around the star beta Pictoris is believed to contain a large number of comet-like bodies(1,2). Transient absorption events as sociated with beta Pictoris have been observed at many wavelengths(3-6 ) and attributed to cometary objects on eccentric orbits passing betwe en the star and the Earth(7). One unexplained aspect of these events i s the large asymmetry between red-shifted and blue-shifted features: s imilar to 90% of the events are red-shifted(6). We show here that such an asymmetry is a natural consequence of the influence on cometary or bits of secular resonances associated with some planetary systems. Res ults from numerical integrations of test particles in a model of our S olar System show that the nu(6) secular resonance excites objects init ially on near-circular orbits to high eccentricities while aligning th eir perihelia. Depending on the location of a distant observer, this a lignment can produce an asymmetry similar to that observed for beta Pi ctoris. Our results imply the presence of at least two planets (a prer equisite for the existence of secular resonances) around beta Pictoris .