[mesa-users] Sudden envelope mixing in a low-mass star, and a segmentation fault in debugging info

[Bill Paxton]

Hi Warrick,

Thanks for digging into this.  I'll take a look a get back to you soon.  

Bill





On Jan 18, 2016, at 7:58 AM, Warrick Ball wrote:

> Hi all,
> 
> Earlier, Earl Bellinger asked me about a suspicious HR track he found in his modelling.  I've attached a plot showing the main sequence: you can see the jumps around the middle (logT ~= 3.88).  I've also attached the relevant inlist.  Just watch out: it saves a *lot* of data (several GB) in the form of all the profiles.  (This is MESA revision 7624.)
> 
> We've been looking at the output and found that the issue appears at model number 1180.  I've attached a plot with the hydrogen abundance at models 1180 and 1181, which are before and after the first jump.  As can be seen, the outer 28% (by radius) of model 1181 appears to be mixed, even though all the diffusion coefficients of mixing are effectively nil.  This also corresponds to a convergence failure, so the first question we have is why the star is behaving this way.
> 
> Diffusion is on and all the metals and helium have settled out of the envelope, but I don't see why this should be a numerical problem.  The back and forth seems to occur as the star mixes part of the envelope, the metals and helium drain out, then the star mixes part of the envelope again (remixes the envelope?), and so on.  But the sudden mixing near the surface is a mystery.
> 
> The second issue is related.  Following Bill Wolf's excellent tutorial [1], I tried to get the debug data for the hydro solver.  You can activate this by uncommenting the last three lines in &controls:
> 
>      ! report_hydro_solver_progress = .true.
>      ! hydro_inspectB_flag = .true.
>      ! hydro_dump_call_number = 1281
> 
> Much to my surprise, this causes a segfault on my machine at hydro call 1272.  I've attached the last ~150 lines from the terminal as "segfault.txt".  The backtrace reads:
> 
> Program received signal SIGSEGV: Segmentation fault - invalid memory reference.
> 
> Backtrace for this error:
> #0  0x7FAB239F4557
> #1  0x7FAB239F4B6E
> #2  0x7FAB22AEBD9F
> #3  0x6B9447 in __hydro_newton_procs_MOD_write_solve_logs
> #4  0x6BA03C in __hydro_newton_procs_MOD_inspectb
> #5  0x69EAA8 in __star_newton_MOD_do_newton
> #6  0x6A1779 in __star_newton_MOD_newton
> #7  0x617D29 in newt.10440 at solve_hydro.f90:0
> #8  0x618F61 in __solve_hydro_MOD_hydro_newton_step
> #9  0x61A697 in __solve_hydro_MOD_do_hydro_newton
> #10  0x61BE46 in __solve_hydro_MOD_do_hydro_converge
> #11  0x627567 in __struct_burn_mix_MOD_do_struct_burn_mix
> #12  0x5200DC in __evolve_MOD_do_evolve_step_part2
> #13  0x40B291 in __star_lib_MOD_star_evolve_step
> #14  0x41D364 in __run_star_support_MOD_run1_star
> #15  0x406AD2 in __run_star_MOD_do_run_star
> #16  0x406B6F in MAIN__ at run.f:0
> ./rn: line 9:  8120 Segmentation fault      ./star
> 
> So the second question we have is why the code segfaults.  I haven't yet dug down into where this is coming from, and I'll try to in the next few days if I have a chance.  For now, any help is as always very welcome and hugely appreciated!
> 
> Cheers,
> Warrick
> 
> [1] http://wmwolf.github.io/projects/mesa_debugging/
> 
> ------------
> Warrick Ball
> Postdoc, Institut für Astrophysik Göttingen
> wball at astro.physik.uni-goettingen.de
> +49 (0) 551 39 5069<inlist_1.0><earl_HR.png><earls_bug.png><segfault.txt>------------------------------------------------------------------------------
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