The physico-chemical history of Falling Evaporating Bodies aroundβPictoris: investigating the presence of volatiles

Abstract

Abstract. Transient spectral absorption events have been monitored for many years toward the star β Pictoris and have been interpreted as resulting from the transit across the line of sight of evaporating comet-sized bodies (Falling Evaporating Bodies, or FEBs). The model shows that these bodies come from circular orbits at > ∼ 4 AU, becoming star-grazers due to planetary perturbations. The physics of the evaporation of those bodies is widely influenced by their physico-chemical properties, especially the presence of volatile matter. We investigate here this question from a modeling point of view, adapting for that case the models designed for solar comets. We simulate the physico-chemical evolution of the FEB progenitors on circular orbits for a time comparable to the supposed age of β Pic, and constrain the quantity of volatiles present in them in relationship with its age and to the semi-major axis of the orbits. We also constrain this semi-major axis by investigating its influence on the dynamical model of FEB generation by planetary perturbations, and show that it is probably less than ∼10 AU. Finally, we show that demanding the FEB progenitors to be icy in a major part of their volume at those distances is probably an unrealistic constraint, and that they more likely look like asteroids with perhaps a small icy nucleus rather than fully icy comets. This result leads to a revision of the FEB evaporation model that has been assumed up to now.

Young Stars Near the Sun

“…Turning to β Pic's extensive surrounding disk, recent papers have focused on one of three areas: (a) the FEB model, (b) the structure of the dusty disk, and (c) the gaseous content of the disk. Karmann et al (2001), Thebault & Beust (2001), and Karmann et al (2003) have considered the flux of FEBs onto β Pic, the need to invoke the gravitational influence of a massive planet, and the physics and chemistry of the sublimation of the volatile and refractory components of the FEBs. Thebault et al (2003) investigated connections between the FEB phenomenon and the production and size distribution of dust particles in the disk within ∼10 AU of β Pic.…”

Dust production from collisions in extrasolar planetary systems

“…The main difficulty is that this refilling has to be very effective and rapid, since the average time needed for a 10 km body at 5 AU to lose all its volatile material is less than 100 years (see Fig. 2 of Karmann et al 2001). 2.…”

Comets: Potential Sources of Prebiotic Molecules for the Early Earth

“…New research topics thus develop on these exocomets (comets orbiting around other stars). The properties of the spectra of a close star, β Pictoris -one of the rare main sequence stars around which a disc has been detected -are currently convincingly interpreted as due to a constant infall of "evaporating bodies" on this star (Lagrange et al, 2000, Karmann et al, 2001. Much is then to be expected from ambitious space experiments under development, like the Corot mission (Baglin 2003), which should make it possible to detect directly comets, as well as Earth-size planets around a wide range of other stars (Lecavelier des Etangs et al, 1999, Bordé et al, 2003.…”