Re: [mesa-users] main sequence problem

[Jakub O. <ost...@as...>]

Hi Matteo,

Thank for you answer. Let me explain or clarify a few things. Or myself :)


>> I can find here four discontinuities. In my opinion this is something which can't be present in any evolution code.
> 
> I am a bit puzzled by this statement. Why you say that? Just because it doesn't look smooth? 

No, not at all. It's because I can't think about single physical reason of such sudden change of Teff.

> If you want to understand what's going on, I suggest you plot profiles of composition across the convective boundary before and after your little discontinuities.
> And you do this for models with different spatial resolution as well. You can do it with bare Schwarzschild and then adding a little overshooting.

I'll take a look at this! I've been testing mostly the behavior of HR so far.

> Again, you speak like you know this has to be an error in the code. But at the same time you just said you don't know what's going on.

For me it looks like an error, but the one that is very easy to ignore or hard to spot. A small change during MS is easy to overlook, especially when you're interested in the later stages.

> I suggest you investigate first the reason for a certain behavior before asking the MESA community for a (n eventual) fix.
> Otherwise I find more appropriate to just point out an interesting behavior, admit you do not understand what's going on, and ask if anybody else had a similar experience / has suggestions towards a better understanding.

I haven't posted it two weeks ago just to check much more things and cases. Now I run out of options so here I am.

> 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.