[mesa-users] instability issue

[Josiah Schwab]

Hi Zoe,

> We are going to study the behaviour of an external field during the
> evolution of star, therefore a second order equation of time and
> radius must be solved inside mesa code. The problem is that for the
> instability to be refused, " dt " must be about 10^(-11) seconds and
> the timesteps between mesa profiles are of order 10^(+15) seconds. Is
> it possible to study such a behaviour and apply the equation in mesa?

It doesn't make much sense to evolve MESA models with a timestep of
10^{-11} s.  Perhaps you could use MESA to generate a series of stellar
models, and then treat everything as "frozen-in" on the short timescale
of interest for your problem.

> Another question is about mesa mesh adjustment and the CFL number. How is
> the CFL number defined in mesa and which quantities does it relate, (dt,dr)
> or (dt,dm) ?

If you're using the hydrodynamics capabilities, then there are CFL-like
controls, e.g.,

  http://mesa.sourceforge.net/controls_defaults.html#dt_div_min_dr_div_cs_limit

but otherwise not.  Remember that MESA does not timestep explicitly.

Best,
Josiah