[mesa-users] Initial default composition

[Bill Paxton]

Hi Jan-Torge,

Thanks for pointing out the inconsistency.
It turns out there is also a comment in star_job_defaults,
and it specifies 2*initial_Z.  sigh.

In the next release, I plan to remove initial_{mass,y,z} from controls.defaults
and replace them by new controls in star_job.defaults along with the
other controls for create_pre_main_sequence_model and
create_initial_model.  It is confusing to have some of the arguments
for the "create" operations living in controls.defaults -- especially
when I write contradictory comments in the two places!

-Bill




On Aug 28, 2013, at 7:07 AM, Max Katz wrote:

> Jan-Torge,
> 
> If I grep in star/private for initial_y, I see that both create_initial_model.f and pre_ms_model.f have the relevant line:
> 
>          if (initial_y < 0) initial_y = max(0d0, min(1d0, 0.24d0 + 2*initial_z))
> 
> This demonstrates that, indeed, the formula actually used by the code is 0.24 + 2*initial_z, and that the formula written in controls.defaults is a typographical error. Thanks for catching it!
> 
> Max
> 
> 
> On Wed, Aug 28, 2013 at 6:23 AM, Jan-Torge Schindler <jtschindler at email.arizona.edu> wrote:
> Hi everyone, 
> 
> I am not sure if this has been discovered before. If so, good!
> 
> I am working with the MESA version 4906 and always create PMS models.
> In the controls.default the following lines are written:
> initial_z = 0.02d0 ! initial metallicity
>          
>             ! initial_z can be any value from 0 to 0.04 when you are creating a pre-main sequence model.
>             
>             ! however, if you are loading a zams model, then initial_z must match one of the prebuilt values.
>             ! look in the 'data/star_data/zams_models' directory to see what prebuilt zams Z's are available.
>             ! at time of writing, only 0.02 was included in the standard version of star.
>          
>          initial_y = -1 ! initial helium mass fraction (< 0 means use default)
>          
>             ! initial_y can be any value you'd like when you are creating a pre-main sequence model.
>             ! for pre-main sequence models, the default for initial_y is 0.24 + 3*initial_z.
> 
> I realized by not specifying the initial composition in my inlist, the following initial composition is chosen:
> Z = 0.02 -> like it should be
> Y = 0.28 -> according to the equation above it should be 0.24+3*0.02 = 0.3 !!!
> Z = 1-X-Y = 0.7 -> should have been 0.68 respectively.
> 
> Running a second inlist with Z=0.01 I realized that the implemented relationship is 
> initial_y is 0.24 + 2*initial_z.
> 
> Maybe I am wrong somewhere and this issue resolves itself. Maybe this is known.
> I am just writing this in case no one stumbled across this before.
> Cheers,
> Jan-Torge 
> 
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