Issue |
A&A
Volume 466, Number 1, April IV 2007
|
|
---|---|---|
Page(s) | 201 - 213 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20053425 | |
Published online | 11 January 2007 |
High latitude gas in the β Pictoris system*
A possible origin related to falling evaporating bodies
Laboratoire d'Astrophysique de Grenoble, UMR 5571 CNRS, Université J. Fourier, BP 53, 38041 Grenoble Cedex 9, France e-mail: Herve.Beust@obs.ujf-grenoble.fr
Received:
13
May
2005
Accepted:
15
December
2006
Context.The puzzling detection of ions at fairly high latitude (
) above the
outer parts of the β Pictoris circumstellar disk was recently reported.
Surprisingly, this detection does not extend to
atoms, in contradiction with
our modelling of the emission lines in and out of the mid-plane of the disk.
Aims.We propose that the presence of these off-plane ions
(and to a lesser extent
atoms), and the non-detection of off-plane
atoms,
could be the consequence of the evaporation process of Falling Evaporating Bodies (FEBs),
i.e., star-grazing planetesimals that evaporate in the immediate
vicinity of the star.
Methods.Our model is two-fold. Firstly, we show numerically and theoretically
that in the star-grazing regime,
the FEBs are subject to inclination oscillations up to
30–, and that most metallic species released during
each FEB sublimation keep track of their initial orbital inclination while starting a free expansion away from the star, blown out by a strong radiation pressure. Secondly,
the off-plane
and
species must be stopped prior to their
detection at rest with respect to the star, about 100 AU away. We revisit the role of energetic collisional processes, and we investigate the possible influence of magnetic interactions.
Results.This dynamical process of inclination oscillations
explains the presence of off-plane (and
). It also accounts for the absence of
because once released by the FEBs, these atoms are quickly photoionized
and no longer undergo any significant radiation pressure. Our numerical simulations demonstrate
that the deceleration of metallic ions can be achieved very efficiently if the
ions encounter a dilute neutral gaseous medium. The required
column density is reduced to
~
, one order of magnitude below
present detection limits. We also investigate the possibility that the ions are slowed down magnetically. While the sole action of a magnetic field of the order of
G is not effective, the combined effect of magnetic and collisional deceleration processes lead to an additional lowering of the required
column density by one order of magnitude.
Key words: stars: circumstellar matter / stars: individual: β Pic / celestial mechanics / methods: numerical / molecular processes / magnetic fields
© ESO, 2007
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