[mesa-users] Initial default composition

[Max Katz]

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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