THE BETA-PICTORIS CIRCUMSTELLAR DISK - XXV - THE CA-II ABSORPTION-LINES AND THE FALLING EVAPORATING BODIES MODEL REVISITED USING UHRF OBSERVATIONS

We present here ultra high resolution observations of the Ca II K and H lines towards beta Pictoris recorded over a period of 3 years and a smaller set of calcium triplet data. At the present resolution, the ce ntral Ca II circumstellar absorption is complex, with several variable components, some of them at very low velocity shifts (< 10 km s(-1)) with respect to the star, in addition to a very narrow stable componen t. The stable component is analyzed and physical informations are deri ved. The variable components at low redshifts are analyzed, and well m odeled in the framework of the Falling Evaporating Bodies (FEB) scenar io previously invoked to explain the absorption features observed at h igher redshifts. We show that the very low redshift events are well si mulated by FEBs crossing the line of sight at somewhat larger distance s from the star than those responsible for the higher velocity redshif t events. The implications of these new observations on the dynamical process responsible for the FEB phenomenon are discussed. In particula r, they put strong constraints on the orbital parameters of the incomi ng bodies that appear in fact in perfect agreement with an origin base d on mean-motion resonances with a massive planet.