Dynamical aspects of the interstellar medium
Description
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 spherical collapse of pre-stellar 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 characteristic 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 scenarios for the fragmentation of the interstellar medium. Finally, 3D numerical simulations with the AMR code RAMSES qualitatively confirm these results. (author)
Abstract (French)
Ce travail de these met en oeuvre la microphysique tres riche du milieu interstellaire dans plusieurs problemes hydrodynamiques a tres haute resolution, tous associes a la formation des etoiles. La premiere partie du travail concerne le developpement d'un modele numerique monodimensionnel que nous avons applique a trois domaines differents. Dans les jets protostellaires, nous degageons les temps de mise a l'etat stationnaire des chocs. Nous precisons les domaines d'application de l'hypothese quasi-stationnaire, et mettons au jour une instabilite liee a la reformation de la molecule H2 dans les chocs dissociants. Pour ces derniers chocs, nous produisons un reseau chimique simplifie qui rendra possible leur etude tridimensionnelle. Dans le cadre des regions de photo-ionisation, nous utilisons le meme code pour discuter le role de l'instabilite de Rayleigh-Taylor dans la formation des structures en piliers observees. Il nous apparait que la gravitation est l'un des principaux responsables de la naissance de cette instabilite. De plus, nous produisons les premieres simulations dynamiques d'un front mixte d'ionisation et de photodissociation. Enfin, le code se revele tres utile pour rendre compte de l'effondrement spherique des condensations prestellaires. Nous confrontons nos modeles a des contraintes observationnelles degagees sur IRAM 04191. Nous montrons que les conditions initiales d'Ebert-Bonnor sont preferables a la sphere singuliere isotherme. Le traitement detaille du transfert de l'energie associe a la chimie des agents refroidissant constitue encore une tres nette amelioration. La deuxieme partie de ce travail se concentre sur l'etude theorique de l'instabilite thermique. L'etude lineaire revele une longueur caracteristique de fragmentation qui fournit un critere de raffinement utile aux maillages a resolution adaptative. L'etude homobare qui predit la repartition de la masse permet aussi de prevoir le cout des simulations avec raffinement de maillage. Ces deux outils analytiques fournissent les premieres pistes vers l'interpretation des spectres de masse observes. L'examen des roles complementaires de la gravite et de l'instabilite thermique permet de formuler des scenarios pour la fragmentation du milieu interstellaire. Enfin, des simulations numeriques tridimensionnelles realisees avec le code RAMSES a raffinement adaptatif de maillage confirment qualitativement ces resultatsFiles
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Additional details
Additional titles
- Original title (French)
- Aspects dynamiques du milieu interstellaire
Publishing Information
- Imprint Pagination
- 181 p.
- Report number
- FRCEA-TH--9240
INIS
- Country of Publication
- France
- Country of Input or Organization
- France
- INIS RN
- 49053093
- Subject category
- S79: ASTROPHYSICS, COSMOLOGY AND ASTRONOMY;
- Resource subtype / Literary indicator
- Thesis
- Descriptors DEI
- COMPUTERIZED SIMULATION; ENERGY TRANSFER; GRAVITATION; MAGNETOHYDRODYNAMICS; PHOTOIONIZATION; R CODES; RAYLEIGH-TAYLOR INSTABILITY; STARS
- Descriptors DEC
- COMPUTER CODES; FLUID MECHANICS; HYDRODYNAMICS; INSTABILITY; IONIZATION; MECHANICS; SIMULATION
Optional Information
- Notes
- 106 refs.; Available from the INIS Liaison Officer for France, see the INIS website for current contact and E-mail addresses; Also available from the INIS Liaison Officer for France, see the INIS website for current contact and E-mail addresses; Also available from Service Commun de la Documentation, 5 rue Thomas Mann Batiment Grands Moulins - Aile B 75013 Paris (France)