[Mesa-users] New to MESA need a bit of understanding

[Warrick Ball]

Hi Nick,

First, as Rob also said, please keep your replies on the mailing list 
(i.e. also reply to `mesa-users at lists.mesastar.org`).  It's useful for 
future users to be able to find previous discussions.

There are some subtle things going on in that paper but you'll do well to 
start comparing your results to theirs e.g. plot something like their Fig. 
1.

I don't think Rob meant for you to use the controls 
`use_accreted_material_j` and `do_element_diffusion` but rather to look at 
the inlists in the test cases `accretion_with_diffusion` and 
`accreted_material_j` to find controls that you should consider adding to 
your own inlist.

Cheers,
Warrick

------------
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, 13 Aug 2019, Nicholas Herrington wrote:

> Hi Warrick,
> Thanks for your email, Im new to MESA, as well as stellar evolution coding in general. I am working on my undergrad project, following a paper on 'The Evolution of Supermassive Population III Stars' (il
> attach to this email). Im trying to replicate the results of the 'initial setup' section 3.1 with MESA. At this moment im working on the 10^-3 Msun/yr accretion rate. I followed the tutorials on the
> sourceforge website and created a simple pre main sequence model. Im adding more controls on top of this for accretion, working through as im trying to understand what to add into my runs. My initial issue
> is I dont understand how the basic pre main sequence model evolves the timestep. My 0.001 Msun/yr run always stops at 2794 Msun with the 'min_timestep' error message (with the basic inlist I sent
> previously). If I reduce the min_timestep in the controls the model runs for longer but gets to 2794 Msun and hangs there for a while. Using what Rob sent me, I have added in use_accreted_material_j and
> do_element_diffusion, this has increased the mass reached to ~4000. I guess my question is how does the timesteps work in MESA because im unsure why, without specifying, the model doesnt run until I stop it.
> Any help with this would be much appreciated. In the mean time, il head to the mailing list and start looking, as well as gather some outputs from the terminal and plot the mass vs radius.
> 
> Thanks
> Nick 
> 
> On Tue, 13 Aug 2019 at 08:18, Warrick Ball <W.H.Ball at bham.ac.uk> wrote:
>       Hi Nick,
>
>       I'll borrow from your reply to Rob but it'll help us to know more
>       precisely what you're trying to do and what you've tried.  I've toyed with
>       "supermassive" stellar models before though it's been a while since I last
>       tried anything and my knowledge of the literature is probably hazy and
>       outdated.
>
>       In your reply to Rob, you wrote:
>
>       > From the work I’m following with the initial conditions in the controls
>       > I’m trying to get the stars to reach 10^4 solar masses.
>
>       Which "work"?  A paper?  Or someone else's inlist?  If so, whose?
>
>       In terms of your timestep problem, have you looked at the output of what
>       your star is doing?  I tried the inlist you sent (2 Msun accreting at
>       0.001 Msun/yr) and you might find it interesting to plot radius as a
>       function of stellar age.  Also, have you searched the mailing list for
>       anything about supermassive stars?  If so, what did you find?
>
>       When asking for help on technical forums, you're more likely to get help
>       if you can demonstrate that you've already tried to help yourself.
>       Hopefully we'll be able to help you learn how to better diagnose the
>       problem and work out a solution that works for your scientific goals.
>
>       Cheers,
>       Warrick
> 
>
>       ------------
>       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 Mon, 12 Aug 2019, mesa-users at lists.mesastar.org wrote:
>
>       > Hi,
>       > Im trying to use the create pre main sequence model along with accretion controls to take a star and make it super massive. Im using specific accretion rates in my runs and my issue occurs with
>       each
>       > accretion rate. Whenever I initiate the run, the star accretes matter until a certain mass (different for each rate) until it stops and prints min timestep error. If I reduce the min timestep
>       in controls it
>       > gets to the same mass as before but runs for longer on that mass, without accreting any futher, then finishes with the same error message (even at very small min timestep values). Ive tried to
>       set the max
>       > mass to no limit in the controls but this hasnt helped either.
>       >
>       > I am not sure how the timestep works with this model and why it accretes to a specific mass everytime reguardless of what time controls I add to the inlist. If anyone could explain or help me
>       understand what
>       > I am doing wrong, that would be much appreciated.
>       >
>       > Thanks
>       > Nick
>       >
>       > OS: Linux distro, Pop OS
>       > MESA-r17701
>       > SDK: I downloaded the may 3 2019 version 
>       >
>       >
> 
> 
>