TYCHO: physics sources

Macroscopic physics derived from:

Dynamics and Gravity

General Relativistic dynamics is used (Van Riper 1979 ApJ 232, 558, with slightly more accurate differences). Explicit hydrodynamics or implicit (hence damped) hydrodynamics (Arnett 1977 ApJS 35, 145) are options at runtime.

Mass loss

For temperatures above 7,500 Kelvin, the mass loss is computed from subroutines provided by Rolf Kudritzki (see Kudritzki, R-P., Puls, J., AnnRevAAp, 38, 613)

For lower temperatures, expressions given in Dupree, A. K. Reimers, D. 1987, or the De Jager expression given in Chiosi and Maeder, 1986, ARAA 24, 336. are used. Several other options are now available.

Envelope

The surface layers are constructed by Bulirsch-Stoer integration of the hydrostatic equations, ignoring nuclear burning. New integrations are done at each time step in order to consistently include changes due to mass loss and mixing. Reproduceability of the integrations is better than one part in a million. For the physics see Kippenhahn and Weigert 1994, and for the mathematics Numerical Recipes 1992.

Atmosphere

An Eddington grey atmosphere is used for optical depths tau below 2/3; Dimitri Mihalas, 1978, Stellar Atmospheres, 2nd Edition, W. H. Freeman and Company: San Francisco, see eq. 3-16.

Radiative Transfer

Equilibrium diffusion of a Black-body gas of photons is used for the radiation transfer for the implicit hydrostatic mode, i.e., standard stellar evolution.

Nonequilibrium diffusion of a Bose-Einstein gas of photons (parameterized by a radiation temperature and a possibly nonzero radiation chemical potential) is used for the explicit hydrodynamic case, with flux limiting to insure a causal rate of flow in optically thin regions.

Convection and Mixing

The default treatment is standard mixing length, and defined in Kippenhahn and Weigert 1994, Stellar Structure and Evolution. Several modifications are to be implemented to make more realistic the description of heat flow, and of the microscopic mixing of composition. The influence of g and p mode waves is being added.

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E-mail:darnett@as.arizona.edu

TYCHO is not public domain software, but is freely available for non-commercial purposes. Absolutely no guarantee is given; use at your own risk...