Re: [mesa-users] main sequence problem

[Matteo C. <ca...@ki...>]

> 
>> Your claim that this makes pointless to study late phases of evolution is also puzzling. I guess your point is that those tiny jumps in L and Teff, that you only get when evolving a massive star with bare Schwarzschild, MLT and all the limitations in your 1D prescriptions, are the biggest sources of uncertainties in the study of advances stages of evolution?
>> Even if it turns out you are right in saying MESA has a problem in the treatment of convective boundaries in the bare Schwarzschild case, from your plots it seems hard this might impact in a serious way post MS results. But of course I might be wrong here. It's just that your statement 'helium burning is seriously affected' is not backed up by any quantitative plot.
> 
> OK, this is interesting point for me because I'm going to use MESA to study stars that might undergo helium burning, but I can't because such a nasty problems like this one. The thing is that helium burning seems to be extremely chaotic in MESA. Every small change of parameters can give you another solution. I had a long thread about it a month ago or so, but I can give you more fresh examples.
> <15m-hr.pdf>
> This is HR diagram for five runs of 15 M_S model. The pink one ('15m v4764') is the one with default mesh and time step. The other four use the same basic inlist but additionally have different modifications of time step or time step and mesh. The physics is the same - OPAL, AGSS09, Z = 0.02, MLT = 1.8, etc. (I attached inlist for '15m tams2'). I haven't changed physics and I obtained very different tracks - isn't it chaotic behavior that doesn't reflect any physical changes?

Ok, just to avoid confusion, you now are raising two different issues:

1) The first issue are the little glitches in the MS of massive stars evolved with the Schwarzschild criterion. This is INDEPENDENT on the resolution, as you have nicely shown.
2) The second issue that now you are discussing, is resolution DEPENDENT. Basically what you are showing is that you have to increase the resolution to obtain convergence of your solution. But this is something well known and that has been extensively discussed in the mailing list (and, for example, during the MESA school). Before trusting your results, you should do a resolution study, to determine if your results are converged. 


> 
>>> Track from WNJ is shown for comparison. The presence of this loop is expected
>> 
>> Is it? Do you have observations of stars with a bare Schwarzschild core showing these objects do a loop at the TAMS???
> 
> No and this is great argument I'm aware of. Nevertheless  the years of testing of WNJ by many great astrophysicists make the results of this code much more trustful than the results of still experimental MESA. The loops are there, but of course they could possibly be artificial.

I fully disagree (with respect to the great astrophysicists that developed and worked on the WNJ code). The results of a code are tested against the observations, not against the number of years a code has been around.  
And in this specific case I don't think you can show any observations supporting one code or the other. 

Cheers,
Matteo

Dr. Matteo Cantiello ------------------------
Kavli Institute for Theoretical Physics 
Room 1226 Kohn Hall CA 93106-4030
University of California, Santa Barbara
---------------- http://matteocantiello.com/