Glossary¶
- AGB¶
Asymptotic giant branch. A late evolutionary stage of low- and intermediate-mass stars, characterised by a cool, extended atmosphere and strong mass loss.
- Carbon star¶
A star whose photospheric carbon-to-oxygen ratio exceeds unity (C/O ratio > 1), so that carbon is available to form amorphous-carbon dust after oxygen is locked in CO.
- C/O ratio¶
The carbon-to-oxygen elemental abundance ratio. Sets the condensable carbon \(\varepsilon_C-\varepsilon_O\).
- Critical point / sonic point¶
The radius \(r_c\) where the wind velocity equals the isothermal sound speed, \(v=c_T\). The wind equation is singular there; the Melia \(\Phi\) transform removes the singularity.
- Degree of condensation¶
\(f_c\), the fraction of condensable carbon locked into dust grains; \(f_c=K_3/c_\mathrm{cond}\).
- Eddington factor¶
\(f_\nu=K_\nu/J_\nu\), the closure of the radiation moment system in the variable-Eddington-factor method.
- Equidistribution¶
The principle behind the movable grid: place nodes so that a monitor function has equal integral in every cell.
- Feautrier method¶
A second-order formulation of radiative transfer along a ray in terms of the mean (\(u\)) and difference (\(v\)) of the in/out intensities, solved as a tridiagonal system.
- Flux-mean extinction¶
\(\chi_F\), the flux-weighted average of the extinction coefficient; the single radiation quantity that sets the radiative acceleration \(\alpha\).
- Henyey method¶
A global Newton–Raphson relaxation of a discretised boundary-value problem on all grid nodes simultaneously. Here an optional wind structure solver.
- Impact parameter¶
A tangent ray at perpendicular distance \(p\) from the centre; the natural coordinate for spherical radiative transfer.
- Mass-loss rate¶
\(\dot{M}=4\pi r^2\rho v\); either prescribed or obtained as an eigenvalue from the critical-point regularity condition.
- Moment method (dust)¶
Tracking the moments \(K_j\) of the grain-size distribution instead of the full distribution; due to Gail & Sedlmayr.
- Nucleation rate¶
\(J_\star\), the rate of formation of seed clusters per unit volume and time (classical nucleation theory).
- Radiative equilibrium¶
The condition that each absorbing component emits as much as it absorbs, \(\int\kappa_\nu(J_\nu-B_\nu)\,\mathrm{d}\nu=0\); fixes the temperature.
- Sphericality factor¶
\(q_\nu\), the geometric factor in the spherical moment equation that accounts for the curvature of the radiation field.
- Unsöld–Lucy correction¶
A robust, approximate temperature correction toward radiative equilibrium, combining the local energy balance and the flux constancy.
- Variable Eddington factor (VEF)¶
The radiative-transfer method in which the moment system is closed with Eddington factors computed from a formal solution and iterated to consistency.