[Mesa-users] pre-main sequence boundary conditions

[Francis Timmes]

this control scales the maximum correction in the newton solver.
if scale_max_correction was 1.0, then the full suggested correction is applied.
if scale_max_correction was 0.1, then the full suggested correction is reduced.
in effect, a damped newton approach.

fxt





> On Oct 8, 2019, at 11:23 AM, TUCHOW, NOAH WOLFE <nxt5109 at psu.edu> wrote:
> 
> Thanks, changing the scale_max_correction did seem to fix the problem. Do you know what exactly scale_max_correction does? It wasn't very clear in the documentation or in 'star/private/star_newton'.
> 
> Thanks again,
> Noah Tuchow
> 
> Hello Noah,
> You can add
> scale_max_correction = 0.1
> to your controls inlist. This helps the Eddington_Grey atmosphere to converge.
> Thomas
> University Innsbruck
> 
> Noah Tuchow
> Penn State University
> Department of Astronomy and Astrophysics
> 532C Davey Lab
> University Park, PA 16802
> 
> 
> On Mon, Oct 7, 2019 at 5:02 PM Noah Tuchow <nxt5109 at psu.edu> wrote:
> Hello everyone, 
> 
> I have a question about atmospheric boundary conditions for pre-main sequence models. I want to initialize a pre-main sequence model (setting  create_pre_main_sequence_model = .true.), save a model file after Deuterium depletion, and then load this model file for the rest of the star's evolution. Previously, I had been using the 'simple_photosphere'  boundary condition until the deuterium birthline and then changing the atmosphere to Eddington grey after loading the model file. However, looking at the evolutionary tracks on the HR diagram, I can see that changing the boundary condition upon loading a model causes a pretty large discontinuity in T and L (see attached image where I load a model file made with the simple_photosphere boundary condition and change to Eddington_grey). I've noticed that this discontinuity disappears if I keep the same boundary condition for both the initialization and the evolution inlists.
> 
> What I would like to do is have the same boundary condition to initialize the model and evolve it through the pre-main sequence and main sequence, so that I can get rid of the discontinuity upon loading. However, I'm having a problem in that I can only get the 'simple_photosphere' and 'photosphere_tables' boundary conditions working for the initialization prior to the deuterium birthline, whereas I would like to get a Grey atmosphere working, such as 'Eddington_grey'. When I try to use the Eddington grey boundary condition in my birthline inlist, MESA exits during the initial relaxation, saying "stopping because of problems dt < min_timestep_limit". I was wondering if there was anything that I could do to get a grey atmosphere working for my birthline model. Are there any tweaks to my inlists which I could do to prevent MESA from exiting during the initial relaxation? Alternatively, are there any ways to reduce the discontinuity upon loading a model with a different boundary condition?
> 
> I've attached my inlist_birthline which I've been using with MESA r11701.
> 
> Thanks for your assistance,
> Noah Tuchow
> 
> 
> Noah Tuchow
> Penn State University
> Department of Astronomy and Astrophysics
> 532C Davey Lab
> University Park, PA 16802
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