Issue |
A&A
Volume 472, Number 1, September II 2007
|
|
---|---|---|
Page(s) | 169 - 185 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20077709 | |
Published online | 09 July 2007 |
Collisional processes and size distribution in spatially extended debris discs*
1
Stockholm Observatory, Albanova Universitetcentrum, 10691 Stockholm, Sweden
2
LESIA, Observatoire de Paris, Section de Meudon, 92195 Meudon Principal Cedex, France e-mail: philippe.thebault@obspm.fr
3
Laboratoire d'Astrophysique de Grenoble (LAOG), Université Joseph Fourier, BP 53, 38041 Grenoble Cedex 9, France
4
Leiden Observatory, PO Box 9513, 2300 RA Leiden, The Netherlands
Received:
24
April
2007
Accepted:
1
June
2007
Context. New generations of instruments provide, or are about to provide, pan-chromatic images of debris discs and photometric measurements, that require new generations of models, in particular to account for their collisional activity.
Aims.
We present a new multi-annulus code for the study of collisionally
evolving extended debris discs.
We first aim to confirm and extend our preliminary result obtained for a single-annulus
system, namely that the size distribution in realistic
debris discs always departs from the theoretical collisional “equilibrium”
power law, especially in
the crucial size range of observable particles (
cm),
where it displays a characteristic wavy pattern. We also study how
debris discs density distributions, scattered light luminosity profiles,
and Spectral Energy Distributions (SEDs) are affected by the coupled effect of
collisions and radial mixing due to radiation pressure affected small grains.
Methods.
The size distribution evolution is modeled over 10 orders of magnitude,
going from μm-sized grains to 50 km-sized bodies. The model takes into
account the crucial influence of radiation pressure-affected small grains.
We consider the collisional evolution of a fiducial, idealized
AU radius disc with an initial surface density
.
Several key parameters are explored: surface density profile,
system's dynamical excitation, total dust mass, collision outcome prescriptions.
Results.
We show that the system's radial extension plays a crucial role and
that the waviness of the size distribution is amplified by inter-annuli interactions:
in most regions the collisional and size evolution of the dust is
imposed by small particles on eccentric or unbound orbits produced
further inside the disc.
Moreover, the spatial distribution of all
grains 1 cm departs significantly from the initial profile
in
,
while the bigger objects, containing most of the system's mass, still
follow the initial distribution.
This has consequences on the scattered-light radial profiles which
get significantly flatter. We propose an empirical law
to trace back the distribution of large unseen parent bodies
from the observed profiles.
We also show that the the waviness of the size distribution has
a clear observable signature in the far-infrared and at (sub-)millimeter
wavelengths. This suggests a test of our collision model, which requires
observations with future facilities such as Herschel, SOFIA, SCUBA-2 and ALMA.
Finally, we provide empirical formulae for the collisional
size distribution and collision timescale which can be used for future
debris disc modeling.
Key words: stars: planetary systems / stars: individual: β Pictoris / stars: planetary systems: formation / stars: circumstellar matter / planets and satellites: formation /
© ESO, 2007
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