Configuration (config.toml)¶

The model is configured by a single TOML file named config.toml in the model folder. It is parsed by agb::ModelConfig (src/config/config.cpp) using toml++.

Conventions¶

Stellar parameters are given in solar units and converted to cgs internally.
The parser is lenient about numeric types: an integer literal also satisfies a floating-point key and vice versa (e.g. resolution = 1000 is accepted for a double field).
Any missing key falls back to a built-in default defined in src/config/config.h. Only the [star] block, the starting model, the spectral grid, and the opacity list are practically required.
Output and data paths are interpreted relative to the model folder (except the opacity path and dust refractive_index_file, which are full paths).

A complete annotated example is shown at the bottom of this page.

`[star]` — stellar parameters¶

Key	Units	Description
`radius`	\(R_\odot\)	Stellar (reference) radius \(R_\star\).
`mass`	\(M_\odot\)	Stellar mass \(M_\star\) (sets gravity).
`luminosity`	\(L_\odot\)	Stellar luminosity \(L_\star\) (the flux target the temperature correction drives toward and the driving luminosity of the wind).
`mass_loss_rate`	\(M_\odot\,\mathrm{yr}^{-1}\)	Mass-loss rate. Used as a prescribed value or as the seed for the eigenvalue solve, depending on the wind setup.
`c_o_ratio`	—	Carbon-to-oxygen ratio. Must be > 1 for a carbon star; the condensable carbon is \(\varepsilon_C-\varepsilon_O\) (all oxygen is assumed locked in CO).

`[model]`¶

Key	Description
`starting_model`	A path to a structure file (format), or the literal `"grey"` to build the Lucy grey bootstrap (see `[grid]`).
`fastchem_parameter_file`	FastChem parameter / element-abundance file (relative to the model folder).

`[spectral_grid]`¶

Key	Units	Description
`min_wavelength`	μm	Lower wavelength bound of the spectral grid.
`max_wavelength`	μm	Upper wavelength bound.
`resolution`	—	Constant spectral resolving power \(R=\lambda/\Delta\lambda\) of the internal grid.
`nb_core_impact_param`	—	Number of impact parameters that intersect the stellar core, used by the ray (impact-parameter) radiative-transfer geometry. Default 20.

`[radiative_transfer]`¶

Key	Default	Description
`nb_iterations`	30	Maximum number of variable-Eddington-factor iterations per RT solve.
`convergence`	1e-4	Relative convergence criterion of the RT iteration.
`use_spline_discretisation`	false	Use cubic-spline (`true`) instead of Taylor finite-difference (`false`) moment discretisation. Keep false: splines lose positivity for optically thick cells (see Radiative transfer).
`flux_from_divergence`	true	Compute the frequency-integrated flux from the flux-divergence form (thesis eq. 2.59), consistent with the moment-equation solve, so \(r^2 H\) is conserved at radiative equilibrium. The per-frequency flux stays on the transport form (eq. 2.58) so the monochromatic spectrum is non-negative.

`[temperature]`¶

This block controls the radiative-equilibrium temperature determination (Radiative-equilibrium temperature correction) and its robustness machinery (Numerical methods and robustness).

Core¶

Key	Default	Description
`nb_iterations`	200	Maximum number of global (outer) temperature iterations.
`convergence`	1e-2	Convergence threshold applied jointly to the flux deviation, the gas and dust energy-balance residuals, and the maximum relative temperature change.
`max_relative_change`	0.005	Per-step cap on \(\|\Delta T\|/T\). Keeps each step small enough for the interleaved hydro–dust cycle to re-converge.
`smooth_profile`	true	Apply a 1–2–1 smoothing pass to the temperature profile.
`force_monotonic`	false	Hard-clip the profile to be strictly outward-decreasing (\(T_i\to0.99\,T_{i-1}\)). Default off — it fights the correction wherever radiative equilibrium wants a flatter profile or a dust-front inversion and drives a ±cap limit cycle.

Full-linearisation corrector¶

Key	Default	Description
`use_linearisation`	true	Enable the full-linearisation (Newton) corrector in addition to / instead of Unsöld–Lucy.
`linearisation_relaxation`	0.5	Global under-relaxation of the Newton step (dust-front stability).
`linearisation_start_unsoeld_lucy`	true	Two-phase corrector: start with the robust Unsöld–Lucy iteration and latch onto the linearisation only once it is safe. Set `false` to linearise immediately (e.g. a warm restart near convergence).
`linearisation_switch_dt_fraction`	0.5	Switch when `max\|dT\|/T` < this × `max_relative_change` …
`linearisation_switch_re_residual`	3e-2	… and the max radiative-equilibrium residual is below this …
`linearisation_switch_count`	3	… for this many consecutive steps (then latch one-way).
`linearisation_flux_constraint`	true	Add the composite flux-constancy term (thesis eq. 3.64/3.65) to the local-RE constraint. See Radiative-equilibrium temperature correction.
`linearisation_xi`	1.0	Weight \(\xi\) of the local radiative-equilibrium term.
`linearisation_zeta_tau_scale`	1.0	Optical-depth scale in \(\zeta(r)=\tau/(\tau+\tau_\mathrm{scale})\), the depth-dependent weight of the flux-constancy term.

Robustness (Unsöld–Lucy under-relaxation and Anderson)¶

Key	Default	Description
`relaxation_init`	1.0	Initial per-layer under-relaxation factor \(\omega\).
`relaxation_min` / `relaxation_max`	0.05 / 1.0	Floor / ceiling for \(\omega\).
`relaxation_down`	0.5	Factor applied to \(\omega\) when the correction flips sign (oscillation).
`relaxation_up`	1.3	Factor applied to \(\omega\) when the correction keeps its sign.
`use_anderson`	true	Enable Anderson mixing on the temperature profile.
`anderson_window`	4	History depth \(m\) of the Anderson mixing.
`anderson_start_iter`	2	Number of plain damped iterations before acceleration starts.
`anderson_activation_fraction`	0.5	Accelerate only once `max\|dT\|/T` < this × `max_relative_change` (the settling regime).

`[hydrodynamics]`¶

Key	Default	Description
`nb_iterations`	200	Maximum number of chemistry–hydrodynamics inner iterations.
`convergence`	1e-2	Relative convergence threshold on the radiative acceleration \(\alpha\).
`use_henyey_solver`	false	Use the Henyey global-Newton structure solver instead of the Melia `Φ` shooting method. See Wind hydrodynamics.

`[grid]` — only used for `starting_model = "grey"`¶

Key	Default	Description
`n_points`	260	Number of logarithmically spaced radial cells.
`inner_radius`	1.0	Inner boundary in units of \(R_\star\).
`outer_radius`	25.0	Outer boundary in units of \(R_\star\).
`gas_opacity`	1.0e-4	Grey gas mass-opacity (\(\mathrm{cm^2\,g^{-1}}\)) that sets the optical-depth scale and hence the photospheric density of the seed.

`[dust]`¶

Key	Description
`refractive_index_file`	Path to the optical constants (complex refractive index vs. wavelength) of the dust material, e.g. amorphous carbon (Rouleau, Maron). Fed to Mie theory to produce the grain absorption/scattering efficiencies.

`[movable_grid]` — adaptive radial grid (default off)¶

See Numerical methods and robustness for the equidistribution scheme.

Key	Default	Description
`enabled`	false	Master switch for the movable grid.
`regrid_frequency`	5	Redistribute nodes every N outer iterations.
`grid_relaxation`	0.1	Under-relaxation \(\omega_\mathrm{grid}\) of the node motion.
`monitor_weight_opacity`	1.0	Weight of the flux-mean extinction in the monitor function.
`monitor_weight_temperature`	0.0	Weight of the gas temperature.
`monitor_weight_nucleation`	1.0	Weight of the dust nucleation rate.
`monitor_weight_velocity`	1.0	Weight of the wind velocity (clusters nodes at the sonic point).
`monitor_smoothing_passes`	4	Number of smoothing passes applied to the monitor.
`monitor_max`	20.0	Cap on the monitor (maximum cell-size ratio).
`monitor_rel_floor`	1e-8	Per-quantity floor relative to its peak.

`[opacity]`¶

Key	Description
`path`	Absolute path to the opacity database (HELIOS-K cross-section folders). The wavenumber grid is read from `<path>/wavenumber_full.dat`.
`species`	An array of `{ symbol = "...", folder = "..." }` tables. `symbol` is the species identifier (e.g. `"CO"`, `"H2O"`, `"CIA-H2-H2"`, `"H-"`); `folder` is the sub-folder of the opacity database holding its cross sections, or `"none"` for species with built-in opacity (continuum / collision-induced, e.g. `H-`, `H2-`, Rayleigh).

`[output]`¶

Each value is a path relative to the model folder; an empty value or "none" disables that output.

Key	Output
`atmosphere`	Converged structure (format).
`spectrum`	Emergent spectrum.
`dust`	Dust distribution and moments.
`hydro`	Wind structure.

Complete example (IRC+10216)¶

# AGB dust-driven wind model configuration (IRC+10216)

[star]
radius         = 1050.0     # R_sun
mass           = 0.7        # M_sun
luminosity     = 3.0e4      # L_sun
mass_loss_rate = 8.0e-5     # M_sun / yr
c_o_ratio      = 1.40

[model]
starting_model          = "atmosphere_converged.dat"   # a path, or "grey"
fastchem_parameter_file = "fastchem_parameters.dat"

[spectral_grid]
min_wavelength = 0.3        # micron
max_wavelength = 50.0       # micron
resolution     = 1000

[radiative_transfer]
nb_iterations             = 40
convergence               = 1.0e-4
use_spline_discretisation = false
flux_from_divergence      = true

[temperature]
nb_iterations       = 300
convergence         = 1.0e-3
max_relative_change = 0.01
smooth_profile      = false
use_linearisation                = true
linearisation_relaxation         = 0.5
linearisation_start_unsoeld_lucy = true
linearisation_switch_dt_fraction = 0.5
linearisation_switch_re_residual = 0.03
linearisation_switch_count       = 3
linearisation_flux_constraint    = true
linearisation_xi                 = 1.0
linearisation_zeta_tau_scale     = 1.0

[hydrodynamics]
nb_iterations     = 60
convergence       = 1.0e-3
use_henyey_solver = false

[dust]
refractive_index_file = "../opacity_data/Amorphous_C_Rouleau.dat"

[movable_grid]
enabled = false

[opacity]
path = "/media/data/opacity_data/helios-k/"
species = [
  { symbol = "CIA-H2-H2", folder = "CIA/H2-H2" },
  { symbol = "CIA-H2-He", folder = "CIA/H2-He" },
  { symbol = "CIA-H-He",  folder = "CIA/H-He" },
  { symbol = "H-",        folder = "none" },
  { symbol = "H2",        folder = "none" },
  { symbol = "He",        folder = "none" },
  { symbol = "H",         folder = "none" },
  { symbol = "H2O",       folder = "Molecules/1H2-16O__POKAZATEL_e2b" },
  { symbol = "CO",        folder = "Molecules/12C-16O__Li2015_e2b" },
  { symbol = "CO2",       folder = "Molecules/12C-16O2__UCL-4000_e2b" },
  { symbol = "C2H2",      folder = "Molecules/12C2-1H2__aCeTY_e2b" },
]

[output]
spectrum   = "spectrum.dat"
atmosphere = "atmosphere.dat"
dust       = "dust.dat"
hydro      = "hydro.dat"

Configuration (config.toml)¶

Conventions¶

[star] — stellar parameters¶

[model]¶

[spectral_grid]¶

[radiative_transfer]¶

[temperature]¶