[mesa-users] Issues with Atmosphere at very low tau

[Richard Monier]

Hello Ehsan,

   I would compute a "real" (more realistic) model atmospheres using 
ATLAS9, for instance, in LTE with non-gray continuous opacities and as 
much line blanketing as necessary to get the temperature profile right 
in the outermost layers.. My own experience with late B stars , which 
are far less massive than your 10 solar mass stars, is that I can 
converge a 72 layers ATLAS9 LTE model up to log tau=-5.00 at Teff around 
12000K and logg=4.00 and solar abundances. Doing so allows to reproduce 
the detailed profiles of Balmer lines much better than a 62 layers model 
that has not been converged so high.

Best wishes,

Richard

On 10/04/2013 06:56 PM, Ehsan Moravveji wrote:
> Hello everyone.
>
> I am looking into how the atmosphere is sampled when we include it to the model, and specifically for a later use in the GYRE.
> I would like to stretch the atmosphere to log_tau = -7.
>
> 1. Among all possibilities available with which_atm_option, only the two T-tau schemes (i.e. Eddington_grey and Krishna-Swamy) do not crash. The rest end up with convergence problem.
> I know that I'm really pushing it beyond the ordinary limit.
> So, I would really like to be able to get the Paczynski_grey and grey_and_kap to work, but do not know where to start.
>
> 2. When I plot the temperature profile, I notice that the outer atmosphere is poorly sampled.
> This is for a 10Msun main sequence star.
> Please take a look at the attached plot. The green line is shifted up for better visibility.
> There exists only and only one point above log_tau~ -3.0 and it is at log_tau=-7.0 (where I put my top of atmosphere).
> To overcome this, I tried to put some T-dependent weight on the meshing:
>
>        use_other_mesh_functions = .true.
>
>        ! temperature gradient
>        ! T_function1 = T_function1_weight*log10(T)
>      T_function1_weight = 110
>        ! T_function2 = T_function2_weight*log10(T / (T + T_function2_param))
>      T_function2_weight = 500
>      T_function2_param = 2d4
>         ! largest change in T_function2 happens around this temperature
>         ! default value puts this in the envelope ionization region.
>         
> but it simply does not give my any improvement.
> Do you guys have any idea how to tackle these two issues?
>
> I have attached the inlist and a model to load from.
>
>
> Thanks.
> Ehsan.
>
>
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