Objectives and Plan

One of the major aims of the project is the implementation of the Laboratory of Computational Astrophysics at the Research Centre for Atomic Physics and Astrophysics, that will allow the continuation and improvement of the numerical study in astrophysics, in a Romanian university. It is worth to mention that the Laboratory will open a new direction for research at the Centre, its applications being much wider that the scientific objectives of the present project.

The main scientific objective of the project is the numerical study of protostellar jets, with novel contributions continuing the advances made during the European network JETSET.

Jets are key components in star formation, extracting the angular momentum from the inner parts of the accretion disk and thus allowing the matter to fall on the central object. The understanding of these phenomena is important for star formation studies but also, in a wider perspective, helps perfecting our knowledge on plasma properties in extreme conditions.

Numerical simulations are a necessary tool in the study of protostellar jets. In this direction, the European project JETSET marked a big step ahead by encouraging the transfer of knowledge that lead to a better cooperation between theorists, astronomers and experimentalists. The proposed project will continue the numerical studies of protostellar jets with a complex approach simulation/observations. The exploration of the parameter space will continue for the discovery of the possible correlations, and on the other hand the results will be compared with the latest astronomical observations. Collaborations with other institutions involved in studies of YSO jets will be established.

For reliable MHD simulations, it is necessary to include non-ideal processes to the adiabatic approximation of ideal MHD. This leads to a much higher computational cost of the simulations, that although reasonable considering the benefits, may become unaffordable in certain conditions. Considering that the price of one CPU hour on the big cluster computers available (also) to the scientific community is of the order of 1 USD/EUR, and that for high resolution simulations of YSO jets tens of thousands CPU hours are used for each simulation, the existence of a local computing facility becomes desirable. This local facility would provide all the computational time needed for the software development process (with validation and testing) and an important part of the time for the scientific computations.

The implementation of the Computational Astrophysics Laboratory will provide (depending on the computing cluster configuration) a local yearly availability of few hundred thousands CPU hours, that will be used in the project for the implementation and testing of new modules in the MHD code employed, as well as the comparison between various MHD simulation codes with astrophysical application. Part of the simulations of YSO jets will also be done on this system. Supplemental computing time for the simulations will be obtained from CINECA Bologna through the cooperation with the Astrophysics group at the University of Turin. At least twenty 2D simulations will be necessary for the satisfactory coverage of the parameter space (jet speed, shock strength, jet density). In this preliminary study various configurations of the initial velocity perturbation, jet radius and perturbation radius and the connection between these parameters and the extension of the peak emission zone will be investigated. The jets to be simulated will be selected from the literature based on their physical characteristics (e.g., the symmetry implied by the cylindrical geometry of the simulation) and of available high-resolution observational data.

The numerical modelling of the selected sources will consist of:
- a review of the available observational data (direct and derived) published for the object regarding the emission, geometry, parameters;
- determination from the observational data of the most probable plasma speed and density at the base of the jet;
- determination of the positions of the shocks producing the enhanced intensity in the emission knots;
- the simulation of each knot, with the determined density and jet base velocity and various shock intensities;
- post-processing of the MHD results to obtain the emissions in observed emission lines;
- construction of the "synthetic jet" by adding the simulated knots at the observed knots positions, convolution with a PSF (Point Source Function) and interpolating at the resolution of the observations;
- comparison with the observed jet.

The outcome of the project will be the results of the YSO jet simulations obtained in the newly equipped Laboratory. These results will be the subject of 2-3 papers published in ISI scientific journals. The scientific results and details on the implementation will be presented at national (2) and international (3-5) conferences. The project will result in the developments of the existing computing infrastructure and a solid foundation for research in computational astrophysics. A laboratory webpage will be built, for the presentation of the results, cooperation proposals and research themes for diploma/master thesis. The project will also be acknowledged during manifestations in the occasion of the International Year of Astronomy 2009 (proclaimed by the UN).

Project proposal, December 2008.