[Mesa-users] problem with small time-steps

Warrick Ball W.H.Ball at bham.ac.uk
Tue Jan 18 09:36:03 UTC 2022

Hi Ebrahim,

I haven't looked at your code but it will be easier for other users to help you if you could describe what at point in evolution the timesteps decrease.  MESA using small timesteps is a fairly generic problem.  Could you attach some plots of, say, an HR diagram?  And could you include the models that do finish?  What's the closest mass to 2 Msun that *does* reach the "final stages" of evolution?

My instinct is that your 2 Msun star is struggling with the thermally-pulsing asymptotic giant branch (TP-AGB) more than the other models.  However, I've also noticed that your `inlist` doesn't include (or, rather, has commented out) the lines for mass loss, so I'm also curious about what are the "final stages" in the evolution of the 1 and 3 Msun models.  Normally the star would lose enough mass during the (TP) AGB to expose the central CO core.  I'm not sure what happens if you try to run without any mass loss and no other stopping condition.



Warrick Ball
Postdoc, School of Physics and Astronomy
University of Birmingham, Edgbaston, Birmingham B15 2TT
W.H.Ball at bham.ac.uk
+44 (0)121 414 4552

On Tue, 18 Jan 2022, mesa-users at lists.mesastar.org wrote:

> Dear Mesa-users
> I edited the run_star_extras.f90 file of the ~/mesa-r21.12.1/star/work star to consider dark matter effects in stars (After copying the files of the star to the Home directory in Ubuntu 20.04). The edited code is working correctly for 1.0 and 3.0
> M_Sun stars. But, when I want to run the code for 2.0 M_Sun, it takes so many steps (at least more than 40000) for the star to reach the final stages of its evolution. In fact, when 2.0 M_Sun star leaves the main-sequence, its time steps become very
> small (~ 1 year and sometimes less than 1 year). And for this reason, it takes so many time-steps for the 2.0 M_Sun star to reach the final stages of its evolution. 
> May I ask what might be the possible reasons for this problem? And how can I solve this problem? And also, why the same problem does not happen for the 1.0 and 3.0 M_Sun stars?
> The attached files are the codes that I used in my work.
> Best regards
> Ebrahim Hassani

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