Dynamical modeling of large scale asymmetries in the beta Pictoris dust disk

We report a new and complete model of the beta Pictoris disk, which succeed s in accounting for both the surface brightness distribution, warp characte ristics, the outer "butterfly" asymmetry as observed by HST/STIS in scatter ed light, as well as the infrared emission. Our model includes the presence of a disk of planetesimals extending out to 120-150,AU, perturbed gravitat ionally by a giant planet on an inclined orbit, following the approach of M ouillet et al. (1997b). At any time, the planetesimal disk is assumed to be the source of a distribution of grains produced through collisional evolut ion, with the same initial orbital parameter distribution. The steady state spatial grain distribution is found incorporating the effects of radiation pressure which can cause the distribution of the smallest particles to bec ome very distended. With realistic assumptions about the grains' chemical p roperties, the modeling confirms the previously evident need for an additio nal population of hot grains close to the star, to account for the 12 mum f luxes at short distances from the star. It also indicates that this populat ion cannot explain the outer 12 mum flux distribution when the effects of g ravity and radiation pressure determine the distribution. Very small grains , produced by collisions among aggregates, are tentatively proposed to acco unt for this 12 mum outer emission.