The effective temperature is one of the basic model parameters and is
specified e.g. with
real teff f=F13.3 b=4 n='Effective Temperature' u=K
(for a relatively cool star).
Note that the actual effective temperature can only be determined a posteriori
and that the entropy of the instreaming entropy (see below) is more important
teff itself. In fact,
teff is only used to control
material properties at the outer boundary. Its value should be close to
the expected effective temperature of the model.
Gravity is another characteristic of a stellar atmosphere. The type (or geometry)
of the external gravity field has to be specified e.g. with
character grav_mode f=A80 b=80 n='Type of gravity field' &
Two values are possible so far:
constant: In the standard ``solar'' case the constant gravity specified with
real grav is directed downward in x3 direction.
central: For the ``supergiant'' case a central potential is assumed with an origin
at x=0. The stellar mass as well as inner and outer smoothing radius have to be specified.
In the case of a constant gravity the amount of the acceleration has to specified with
real grav f=E15.8 b=4 n='Gravity' u=cm/s^2
Setting this value to zero switches off gravity (oh wonder).
In the case of a central the mass (in cgs units) of the star has to be specified with
real mass_star f=E15.8 b=4 n='Stellar Mass' u=g
To avoid the central singularity in a 1/r potential it is smoothed in
the center to give a central potential of 1/
r0_grav, specified with
real r0_grav f=E15.8 b=4 n='Inner Smoothing Radius' u=cm
This parameter should always be non-zero for a central potential.
The density in an atmosphere in hydrostatic equilibrium can decline to very
low values. To artificial enlarge the pressure (and density) scale height
in the outer layers of the star (the corners of the box) the gravity can
be reduced by defining the potential at infinity to be
r1_grav, specified with
real r1_grav f=E15.8 b=4 n='Outer Smoothing Radius' u=cm &
Setting this parameter to zero gives the usual 1/r behavior of the potential
in the outer layers but also chooses another smoothing formula in the central
c0='0.0: Not used'
real r0_grav is relevant).
But a value somewhat larger than the remotest corner of the box effectively
cancels this artificial smoothing in the outer layers without changing
the formula for the potential.
For a ``Star-in-a-Box'' and particularly when only ``simple'' ray directions are allowed
in the radiation tranport step the temperature in the outer corners of the box tends to
become very small. To artificially increase the effect of radiative heating the
real r1_rad can specify a radius beyond which only postive contributions
of the radiative energy transport to the energy budget are taken into account. This
ruins the conservativity of the code in these layers and should be applied only in very
remote corners which are then considered only as sort of extended boundary region but
not as part of the ``real'' model.
The parameter can be specified e.g. with
real r1_rad f=E15.8 b=4 n='Outer radiation transport radius' u=cm &
A value of
c0='0.0: Not used'
0.0 (default) or below deactivates this feature.