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Aspects dynamiques du milieu interstellaire

Abstract : This work deals with the very rich microphysics of the interstellar medium
in several hydrodynamical problems at very high resolution, all associated
to star formation.

The first part of this study concerns the implementation of a numerical
1D hydrodynamical code which we applied to three different fields.

In protostellar jets, we compute the time delay for shocks to get
to steady state. We explore the applicability of the quasi-stationary
hypothesis and unveil an instability linked to H2 molecule reformation
in dissociative shocks. For this last type of shocks, we produce
a reduced chemical network for future 3D studies.

In the context of photoionisation regions, we use the same code to
discuss the role of the Rayleigh-Taylor instability in the
formation of elephant trunk structures observed. It appears that
gravitation is one of the main actor responsible for the birth of the instability.
Besides, we produce the first dynamical simulations of a mixed front
of photo-ionisation and photo-dissociation.

Finally, the code turns out to be quite useful to account for the shperical
collapse of prestellar condensations. We confront our models to observational
constraints on IRAM 04191. We show that Bonnor-Ebert initial conditions
are much better than the singular isothermal sphere. The detailed treatment
of the energy transfer associated with the chemistry of cooling agents improves
significantly further the match between the models and the observations.

The second part of this work focuses on the theoretical study of thermal
instability. The linear study reveals a characterstic
fragmentation length scale which yields a refinement criterion useful
for adaptive meshes. The study at uniform pressure predicts the mass
density probability function and also allows to cost estimate the
adaptive mesh refinement simulations. Both these analytical tools are
first hints towards the interpretation of observed mass spectra.
Further scrutiny of the complementary roles of gravity and thermal
instability allows to devise scenarii for the fragmentation of the
interstellar medium. Finally, 3D numerical simulations with the AMR
code RAMSES qualitatively confirm these results.
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Contributor : Pierre Lesaffre <>
Submitted on : Wednesday, January 10, 2007 - 4:44:11 PM
Last modification on : Friday, October 23, 2020 - 4:39:03 PM
Long-term archiving on: : Tuesday, April 6, 2010 - 9:54:31 PM

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  • HAL Id : tel-00123712, version 1

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Pierre Lesaffre. Aspects dynamiques du milieu interstellaire. Astrophysique [astro-ph]. Université Paris-Diderot - Paris VII, 2002. Français. ⟨tel-00123712⟩

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