A&A 401, 577-592 (2003)
The origin of crystalline silicates in the Herbig Be star HD 100546 and
in comet Hale-Bopp
J. Bouwman1, 2, A. de Koter1, C. Dominik1 and L. B. F. M. Waters1, 3
Astronomical Institute "Anton Pannekoek", University of Amsterdam,
Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
CEA, DSM, DAPNIA, Service d'Astrophysique, CE Saclay, 91191 Gif-sur-Yvette Cedex, France
Instituut voor Sterrenkunde, K.U. Leuven, Celestijnenlaan 200 B, 3001
(Received 8 April 2002 / Accepted 9 January 2003 )
We have investigated the spatial distribution, and the
properties and chemical composition of the dust orbiting HD 100546.
This system is remarkably different from other
isolated Herbig Ae/Be stars in both the strength of the mid-IR excess
and the composition of the circumstellar dust.
To explain spectral features and the amount of mid-IR dust emission
the presence of a component of
m) grains radiating at ~200 K is required,
which is not seen in other well investigated Herbig Ae/Be systems.
This additional component is inconsistent with a uniform flaring disk model.
The fraction of intercepted stellar light that is absorbed
and re-emitted in the mid-IR is so large (~70%) that it
requires the disk to be more "puffed up" at about 10 AU, where
the grains have
K. This may occur if a
proto-Jupiter clears out a gap at this distance allowing direct
stellar light to produce an extended rim at the far side of the
The other remarkable difference with other isolated Herbig Ae/Be systems
is the presence of a much larger mass fraction of the crystalline silicate forsterite
in the circumstellar dust.
We find that the mass fraction of crystalline silicates in
HD 100546 increases with decreasing temperature, i.e. with
larger radial distances from the central star. This distribution
of crystalline dust is inconsistent with radial mixing models
where the crystalline silicates are formed by thermal annealing
above the glass temperature in the very inner parts of the
disk, and are subsequently transported outwards and mixed
with amorphous material.
We speculate that the formation and spatial distribution of the crystalline dust
may be linked to the formation of a proto-Jupiter in the disk around HD 100546.
Such a proto-Jupiter could gravitationally stir the disk leading to a
collisional cascade of asteroidal sized objects producing small crystalline grains,
or it could cause shocks by tidal interaction with the disk which might produce
crystalline dust grains through flash heating.
As shown by Malfait et al. (1998), the infrared spectrum of HD 100546 is
very similar to that of C/1995 O1 Hale-Bopp (Crovisier et al. 1997).
Using an identical methodology, we have therefore also studied this
solar system comet. Both objects have an almost identical grain composition, but
with the important difference that the individual dust species in
Hale-Bopp are in thermal contact with each other, while this is not the case in HD 100546.
This suggests that if similar processes leading to the dust composition as seen in HD 100546
also occurred in our own solar system, that Hale-Bopp formed after the formation
of one or more proto-gas giants.
circumstellar matter --
stars: formation --
Offprint request: J. Bouwman, firstname.lastname@example.org
© ESO 2003