Issue |
A&A
Volume 408, Number 2, September III 2003
|
|
---|---|---|
Page(s) | 775 - 788 | |
Section | Planets and planetary systems | |
DOI | https://doi.org/10.1051/0004-6361:20031017 | |
Published online | 17 November 2003 |
Dust production from collisions in extrasolar planetary systems
The inner β Pictoris disc
1
Observatoire de Paris, Section de Meudon, 92195 Meudon Principal Cedex, France
2
CEA Saclay, Centre de l'Orme des Merisiers, 91191 Gif-sur-Yvette Cedex, France
3
Leiden Observatory, PO Box 9513, 2300 Leiden, The Netherlands
4
Laboratoire d'Astrophysique de l'Observatoire de Grenoble, Université J. Fourier, BP 53, 38041 Grenoble Cedex 9, France
Corresponding author: P. Thébault, philippe.thebault@obspm.fr
Received:
21
March
2003
Accepted:
19
June
2003
Dust particles observed in extrasolar planetary discs
originate from undetectable km-sized bodies but this valuable
information remains uninteresting if the theoretical link between
grains and planetesimals is not properly known. We outline in this
paper a numerical approach we developed in order to address this
issue for the case of dust producing collisional cascades.
The model is based on a particle-in-a-box method. We follow the
size distribution of particles over eight orders of magnitude in
radius taking into account fragmentation and cratering according
to different prescriptions. Particular attention is paid to
the smallest particles, close to the radiation pressure induced cut-off size
Rpr, which are placed on highly eccentric orbits by the stellar
radiation pressure.
We applied our model to the case of the inner (<10 AU) β Pictoris disc, in
order to quantitatively derive the population of progenitors needed
to produce the small amount of dust observed in this region
(1022 g). Our simulations show that the collisional
cascade from kilometre-sized bodies to grains significantly departs from
the classical
power law: the smallest particles
(
) are strongly depleted while an overabundance of
grains with size ∼2Rpr and a drop of grains with size
100Rpr develop regardless of the disc's dynamical excitation, Rpr
and initial surface density. However, the global
dust to planetesimal mass ratio remains close to its
value. Our rigorous approach thus confirms the depletion in mass in
the inner β Pictoris disc initially inferred from questionable
assumptions. We show moreover that collisions are a sufficient source
of dust in the inner β Pictoris disc. They are actually unavoidable even
when considering the alternative scenario of dust production by slow
evaporation of km-sized bodies. We obtain an upper limit of
0.1
for the total disc mass below 10 AU. This upper limit is
not consistent with the independent mass estimate
(at least
) in the frame of the
Falling Evaporating Bodies (FEB) scenario explaining
the observed transient features activity. Furthermore, we show that the mass
required to sustain the FEB activity implies a so important mass loss
that the phenomena should naturally end in less than 1 Myr, namely in
less than one twentieth the age of the star (at least
years).
In conclusion, these results might help converge towards a coherent picture
of the inner β Pictoris system: a low-mass disc of collisional debris leftover
after the possible formation of planetary embryos, a result which would be coherent with the estimated age of the system.
Key words: stars: planetary systems / stars: individual: β Pictoris / stars: planetary systems: formation
© ESO, 2003
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