www.univ-­‐amu.fr www.lam.fr PhD Thesis PhD thesis director name: Pierre BARGE Email: [email protected] Phone number: +33 4 91 05 59 84 Co-­‐director: [email protected] PhD title: Forming planetesimals in vortices Subject description: The subject of this thesis focuses on the evolution of protoplanetary disks at the stage when the dust and gas they contain are still coupled to one another. Numerical and theoretical works show that, at this stage, various instabilities can produce persistent gaseous structures or vortices that could play a crucial role in dust agglomeration processes and disk evolution. This idea was recently supported by ALMA observations reporting the discovery of disk asymmetries in the disk of young stars (e.g. Van der Marel et al. 20139; Fukagawa et al. 2013; Cassasus et al. 2013). These observations are, indeed, frequently explained as clouds of solid particles trapped in large scale and persistent vortices. The goal of the thesis is to study the evolution of solid particles trapped in protoplanetary vortices and to explore the possibility they concentrate in the core of the vortices to form self-­‐gravitating clumps, possibly at the origin of the planetesimals. The first step of the thesis will be to study the confinement of the solid particles captured in a 2D gaseous vortex and to determine the conditions for the formation of high-­‐density blobs that are expected to collapse and form primordial bodies. Two competing effect will be taken into account: (i) self-­‐gravity that increases the concentration of the solid material in the core and (ii) dust/gas instabilities4,5,6 that tend to weaken the vortices due to the back reaction of the particles onto the gas. The respective importance of the two effects will be studied and analyzed thank to numerical simulations performed with a bi-­‐fluid code that accounts for disk self-­‐gravity. The second step will be to explore the capture and confinement mechanisms in a 3D context. The evolution of a 3D columnar vortex will be studied when loaded with solid particles. In this case the solid particles tend to, (i) sediment under the vertical component of the star gravity and, (ii) drift toward the vortex center, since unaffected by the pressure force. Here, the goal is to study the formation of a high-­‐density region in the equatorial layer of the disk and to follow its evolution against Kelvin-­‐Helmoltz4 and dust/gas instabilities5,6. This question will be addressed using the 3D version of the code. The numerical tool to address the problems is a bi-­‐fluid code specifically developed and optimized to study the evolution of protoplanetary disks 2,7,8 . This code uses the finite volume method and can work in 2D or 3D; it solves the fully compressible inviscid Euler’s equations for a perfect gas in non-­‐homentropic conditions and for particles in a fluid approximation. The solid particles are fully coupled to the gas by aero-­‐dynamical forces. The code is parallelized in OpenMP/MPI and can run on National computing resources. A further development of the code would be to extend self-­‐gravity capability from 2D to 3D. The applicant should be familiar with problems of fluid mechanics and have a sufficient skill in the use and management of numerical codes. He (she) will work at LAM with access to the local OpenMP/MPI cluster and the national computing resources allocated to the project. Bibliography : 1
Barge, P., Ricci, L., Carilli, C. & Previn, R. A&A (submitted) 2 Barge,P., Richard,S. & Le Dizes, S. 2016A&A...592A.136B 3 Inaba, S. ; Barge,P. : Daniel,E. ; Guillard,H. 2005A&A...431..365I 4
Johansen, A. et al. 2006ApJ...643.1219J 5
Johansen, A. et al. 2007Natur.448.1022J 6 Raettig, N., Klahr, H. & Lyra, W. 2015ApJ...804...35R 7
Richard, S. ; Barge, P. and Le Dizès, S. 2013A&A...559A..30R 8
Surville, C. and Barge, P. A&A 2015A&A...579A.100S 9
Van der Marel, N. et al. 2013Sci...340.1199V