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Interstellar Turbulence and hierarchical structuring

Interstellar Turbulence and hierarchical structuring. Nicolas Décamp (Univ. della Calabria) Jacques Le Bourlot (Obs. de Paris). Outline. The context Interstellar medium Turbulence Interstellar Turbulence The model Velocity field synthesis Coupling with the density field Chemistry.

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Interstellar Turbulence and hierarchical structuring

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  1. Interstellar Turbulence and hierarchical structuring Nicolas Décamp (Univ. della Calabria) Jacques Le Bourlot (Obs. de Paris)

  2. Outline • The context • Interstellar medium • Turbulence • Interstellar Turbulence • The model • Velocity field synthesis • Coupling with the density field • Chemistry

  3. The interstellar medium • Dust and gas • 10% of the stellar mass • H:70%, He:28% (in mass) • Diverse regions: Ionised, atomic and molecular regions • Numerous processes: electromagnetic radiations, gravitation, magnetic field, chemistry, turbulence

  4. Chemistry and time scales

  5. Turbulence • Kolmogorov 41 • Scale exponent h=1/3 • Structure functions:

  6. Intermittency

  7. Interstellar Turbulence • High Reynolds number • Non-thermic lines

  8. Interstellar Turbulence • High Reynolds number • Non-thermic lines Ref: Falgarone E. et al., 1994, Ap. J., 436, 728

  9. Interstellar Turbulence • High Reynolds number • Non-thermic lines • Scale laws • Cloud structure • Effect of turbulent diffusion on chemistry • Intermittency (CH+)

  10. Evolution through scales of centroids velocity increments IRAM key-project Ref: Falgarone E., Panis J. F., Heithausen A. et al. 1998, A&A, 331, 669

  11. Wavelets • Local in position t0 and space Dt • Wavelet coefficients • Reconstruction

  12. Wavelet analysis => PDF at various scales From one scale to another: Propagator Log-normal model: 2 parameters Synthesis using this propagator. Ref: Arnéodo A., Muzy J.-F. & Roux S. G. 1997, J. Phys. II (France),7, 363 Analysis and synthesis of the velocity field

  13. Synthesis of the velocity field • Multi-resolution analysis • Cj,k=approximation coefficient • Dj,k=wavelet coefficient • Cascade: Mj follow the log-normal model

  14. Comparison Model/Observation PDF of the velocity increments at various scales

  15. Standard deviation of the velocity field as a function of scale

  16. One-dimensional Model • 2D velocity field • Hypothesis: homogeneous, isotropic and stationary turbulence • => 1D velocity field evolving with time • Density field from the mass conservation equation

  17. Density field

  18. Density as a function of scale

  19. For a realistic chemistry • 35 species • Bistability • Example: T=10.3K and x= 5.10-17 s-1 Ref: Le Bourlot J., Pineau des Forets G., Roueff E. 1995, A&A, 297, 251

  20. Chemistry K1 is temperature dependant and the reaction (4) is exothermic Normalisation: Equilibrium, Stability :

  21. Different structures for the different species

  22. Phase space and time scales

  23. Conclusion • Analysis and reconstruction of an interstellar turbulent velocity field with a small number of parameters. • Test of eventual deviations / log-normal model => much larger maps • Possible 2D or 3D generalisation • Different distributions for different species without any external mechanism. • More realistic chemistry…

  24. First results

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