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