Interstellar Turbulence: Theory, Implications and Consequences
Interstellar Turbulence and hierarchical structuring
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Transcript of Interstellar Turbulence and hierarchical structuring
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Interstellar Turbulence and hierarchical structuring
Nicolas Décamp (Univ. della Calabria)
Jacques Le Bourlot (Obs. de Paris)
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Outline
• The context – Interstellar medium– Turbulence– Interstellar Turbulence
• The model– Velocity field synthesis– Coupling with the density field– Chemistry
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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
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Chemistry and time scales
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Turbulence
• Kolmogorov 41
• Scale exponent h=1/3• Structure functions:
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Intermittency
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Interstellar Turbulence
• High Reynolds number
• Non-thermic lines
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Interstellar Turbulence
• High Reynolds number
• Non-thermic lines
Ref: Falgarone E. et al., 1994, Ap. J., 436, 728
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Interstellar Turbulence
• High Reynolds number
• Non-thermic lines
• Scale laws
• Cloud structure
• Effect of turbulent diffusion on chemistry
• Intermittency (CH+)
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Evolution through scales of centroids velocity increments
IRAM key-projectRef: Falgarone E., Panis J. F., Heithausen A. et al. 1998, A&A, 331, 669
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Wavelets
• Local in position t0 and space t
• Wavelet coefficients
• Reconstruction
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Analysis and synthesis of the velocity field
• 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
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Synthesis of the velocity field
• Multi-resolution analysis– Cj,k=approximation coefficient
– Dj,k=wavelet coefficient
• Cascade:
Mj follow the log-normal model
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Comparison Model/Observation
PDF of the velocity increments at various scales
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Standard deviation of the velocity field as a function of scale
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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
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Density field
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Density as a function of scale
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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
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Chemistry
K1 is temperature dependantand the reaction (4) is exothermic
Normalisation:
Equilibrium,Stability :
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Different structures for the different species
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Phase space and time scales
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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…
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First results