The physico-chemical history of Falling Evaporating Bodies around β Pictoris: The sublimation of refractory material

¹ Laboratoire d'Astrophysique de Grenoble, Université J. Fourier, BP 53, 38041 Grenoble Cedex 9, France
² Laboratoire de Planetologie de Grenoble, Université J. Fourier, BP 53, 38041 Grenoble Cedex 9, France

Corresponding author: H. Beust, herve.beust@obs.ujf-grenoble.fr

Received: 20 December 2002
Accepted: 3 June 2003

Abstract

Transient spectral redshifted absorption events in the spectrum of β Pictoris (β Pic) have been attributed to comet-like bodies falling toward the star (Falling Evaporating Bodies, or FEB) and evaporating in its immediate vicinity. Dynamical models shows that these bodies originate from circular orbits at AU. After an eccentricity increase due to planetary perturbations, they end up as star-grazers. The physics of the cloud generated by the body's sublimation is highly influenced by the physico-chemical conditions inside the body. Thus it is necessary to investigate the composition and the behavior of the materials within the body in order to explain the observed features. The physico-chemical evolution of the bodies has been simulated during all the phases before and during their FEB state. First the fluctuations in the gas production rates of volatile solids in the first phase when the refractory materials have not yet evaporated has been studied. Later on, the refractory crust of the object evaporates even if the core still contains volatile solids. The simulation then shows a phase lag between the production rate of volatiles and of refractory materials during the periastron passage. The influence of dynamical and physical parameters on the FEB phenomenon are also investigated. We find that only a heterogenous population of bodies can produce all the absorption features that have been observed so far. These results are important for the understanding of the FEB phenomenon and can lead to a revision of the FEB sublimation model.