Internal Structure of Stars
Joachim Köppen Kiel/Strasbourg March 2013
Warning: some of the features of this applet are not
fully functional yet! Also, the opacity table is rather simple,
so that radiative and convective equilibrium models are only
very approximate!!
Some quick explanations of the applet's use:
Left hand buttons
- Input Data: shows the input parameter page
- T-Rho plot: shows the plot of central temperature
and density, which is used to start the simulation
- clear T-Rho plot
T-Rho Plot
- to operate, select on the right hand side e.g. the
radius-mass plot; clicking on the T-Rho plot will
start the computation, whose result is displayed on
the radius-mass plot. The aim is to find the initial
T-Rho combination which ends up in the desired mass
at the desired stellar radius. The initial dot is
marked with a colour depending on the outcome.
- blue = stellar mass reached
- cyan = stellar radius reached
- green = low surface pressure reached
- gray = low surface temperature reached
- shades of red indicate that several surface conditions
have simultaneously been reached
- the parameter values of the last model are displayed in
TextFields on the input parameter page, where they can be
modified manually ...
Left hand Page
- Model Type: here one can choose between isothermal,
polytropic, purely radiative, and radiative/convective
models
- hitting enter key in the following TextFields starts computation
- comput.accuracy: a tolerance for the radial step width
- stellar mass
- stellar radius
- polytropic index
- opacity: this scaling factor has been set to give a solar
model in radiative equilibrium ...
- central temperature
- helium mass fraction
- metal mass fraction
- last x guess: the parameter (T or K) of last simulation
- last y guess: log(central_density) of last simulation
- stellar radius: shows the result of last simulation
- stellar luminos.: shows the result of last simulation
Right hand buttons
- Plots: updates the plot
- Overplot: switches on/off the overplotting of all curves
- clear: erases all present curves and dots
- start: (re-)starts the simulation with the last guess
parameters given on the left hand panel (or from the T-Rho plot)
- stop: halts the current simulation
- resume: continues with the halting simulation
- drag&zoom: click the button, then drag the mouse over that region of
the plot which you want to zoom in. Then re-run the simulation
- unZoom: brings back the full view of the plot, but you have to re-run
to restore the curve(s)
Right hand plots
- Plots: does not do anything (yet)
- Sing.Curve: switches on/off the overplotting of all curves
- the abscissa and ordinate can be chosen among these
variables: radius, mass, density, pressure, temperature,
luminosity, energy fraction from CNO cycle, ratio of
radiation pressure and gas pressure, fraction of convective
flux (note: some of the features are not yet implemented).
For an example, here is the screen shot of the search for radiative
equilibrium models for the Sun. Models that give both the mass and
the radius of the Sun are found only in a small region of values
for central temperature and density (reddish dots).
Here, we look in a smaller part of the central parameter space, in
order to find models with low surface temperature. The gray dots
indicate models whose temperature drops rapidly before the solar
surface is reached.