Atmospheric Model for Asymptotic Giant Branch Stars

This is the documentation of a self-consistent model for the stationary, spherically symmetric, dust-driven wind of a carbon-rich asymptotic giant branch (AGB) star. The code couples

• a spherical, frequency-dependent radiative transfer solver using the Rybicki–Hummer variable-Eddington-factor moment method,

• a radiative-equilibrium temperature determination (Unsöld–Lucy correction and a full-linearisation Newton corrector),

• equilibrium gas-phase chemistry (FastChem),

• carbon-dust nucleation and growth following Gail & Sedlmayr, using the moment method with self-consistent carbon depletion, and

• a stationary wind hydrodynamics solver (Melia Φ transform with a mass-loss eigenvalue, plus an optional Henyey global-Newton structure solver),

iterated to a self-consistent stationary outflow.

Note

The model is research software and under active development. This documentation reflects the implementation on the main branch. The underlying radiative-transfer scheme and notation follow the diploma thesis of D. Kitzmann; equation numbers of the form (2.59), (3.64), … below refer to that thesis.

Getting started

• Overview
  • Scientific context
  • What the code computes
  • The solution strategy in one paragraph
  • Status and validation
• Installation and building
  • Requirements
  • Bundled / fetched dependencies
  • Building
  • Self-test
  • Running a model
• Running a model
  • Invocation
  • Model folder layout
  • Starting model
  • Structure file format
  • Output files
  • Console diagnostics
• Configuration (config.toml)
  • Conventions
  • [star] — stellar parameters
  • [model]
  • [spectral_grid]
  • [radiative_transfer]
  • [temperature]
  • [hydrodynamics]
  • [grid] — only used for starting_model = "grey"
  • [dust]
  • [movable_grid] — adaptive radial grid (default off)
  • [opacity]
  • [output]
  • Complete example (IRC+10216)

Theory and modelling

• Theory and modelling
  • The coupled problem and the solution loop
  • Radiative transfer
  • Radiative-equilibrium temperature correction
  • Gas-phase chemistry (FastChem)
  • Dust formation (Gail & Sedlmayr)
  • Opacities (transport coefficients)
  • Wind hydrodynamics
  • Numerical methods and robustness
  • Notation
• The coupled problem and the solution loop
  • The two physical structure equations
  • Energy: radiative equilibrium
  • The solution loop
  • Convergence criteria
• Radiative transfer
  • Method overview
  • Geometry: impact parameters and tangent rays
  • Formal solution on a ray (Feautrier)
  • The moment system for \(J_\nu\)
  • Taylor vs. spline discretisation
  • Two flux definitions and why they coexist
  • Outputs of the RT module
  • The linearised moment operator
• Radiative-equilibrium temperature correction
  • Why two temperatures
  • Unsöld–Lucy correction
  • The decisive subtlety: the ratio form of the constraint
  • Full-linearisation (Newton) correction
  • Local RE alone is not enough: the flux-constancy term
  • Two-phase corrector and coupled-loop stability
  • Anderson acceleration
  • Accuracy achieved
• Gas-phase chemistry (FastChem)
  • Interface
  • Carbon depletion coupling
  • Equation of state
• Dust formation (Gail & Sedlmayr)
  • The moment equations
  • Nucleation rate
  • Carbon depletion in a single causal sweep
  • Outputs and dust opacity
  • Coupling to the hydrodynamics
• Opacities (transport coefficients)
  • Gas opacities
  • Spectral grid and sampling
  • Dust opacities
• Wind hydrodynamics
  • The radiative acceleration
  • The Melia \(\Phi\) transform
  • Critical point and the mass-loss eigenvalue
  • Shooting solution (default)
  • The grey (Lucy) starting model
  • Optional: the Henyey global-Newton structure solver
  • Prescribed vs. eigenvalue mass-loss rate
• Numerical methods and robustness
  • Fixed-point structure and convergence tests
  • Adaptive per-layer under-relaxation
  • The per-step cap
  • Anderson acceleration
  • Movable (adaptive) radial grid
  • Reproducibility
  • Performance notes

Implementation

• Architecture
  • Entry point
  • The top-level model object
  • Control flow
  • Persistent iteration state
  • Third-party libraries
• Source tree guide
  • model_main/
  • agb_model/
  • config/
  • spectral_grid/
  • atmosphere/
  • chemistry/
  • transport_coefficients/
  • radiative_transfer/
  • temperature_correction/
  • dust/
  • hydrodynamics/
  • additional/
• File formats
  • Input
  • Output

Appendix

• Glossary
• References

Indices and tables

• Index

• Search Page