[mesa-users] Initial Helum Abundance [He/H]

[Pablo Marchant]

Hi Ehsan. Given that the mass fractions for H1 and He4 are correct, then
the abundance that comes out must be good unless there is a small
arithmetic error. As a simple check,

12+log10(0.2485/0.7381) = 11.53
12+log10(0.2485/0.7381/4) = 10.93

so my guess is that chem_isos% Z_plus_N(i) is for some reason returning 1
for He4

On Sun, Nov 2, 2014 at 1:54 PM, Ehsan Moravveji <e.moravveji at gmail.com>
wrote:

> Hello everybody,
> I came across a discrepancy with the initial abundance of an arbitrary
> model that I would like to share with you. But, let me patiently walk you
> through some simple steps.
>
> 1. You can specify your desired mixture (z_frac) and composition (X, Y, Z)
> from the star_job part of the inlist. So, I stick to the default Asplund et
> al. (2009), and here is my take:
>
>        initial_zfracs = 6
>       change_initial_Y = .true.
>       new_Y = 0.2485d0
>       change_initial_Z = .true.
>       new_Z = 0.0134d0
>
> 2. To make sure I made the right pick of Y and Z, I check with
> mesa/chem/public/chem_def.f, and there we have:
>
>       real(dp), parameter :: AGSS09_zsol = 0.0134d0
>       real(dp), parameter :: AGSS09_ysol = 0.2485d0
>
> 3. Looking at Table 1 in Asplund et al. (2009), I see that the solar
> helium abundance in spectroscopic notation is [He/H] = 10.93 +/- 0.01.
>     So far, so good! Now, I would like to ensure my initial mixture in
> MESA is exactly the same as the reference.
>
> 4. I add the following simple block in my extras_startup() to print out
> the initial abundances in mass fraction and number fraction (in
> spectroscopic notation)
>
>          allocate(xa_orig(s% species), na_orig(s% species))
>           do i = 1, s% species
>             xa_orig(i) = s% xa(i, 1)
>             na_orig(i) = 12d0 + dlog10(s% xa(i, 1) / (s% xa(1,1) *
> chem_isos% Z_plus_N(i) ))
>          enddo
>
>          write(*,'(a5, a10, 2a16)') 'i', 'Name', 'X_i', 'N_i'
>          do i = 1, s% species
>             write(*,'(i5, a10, 2e16.4)') i, chem_isos% name(s%
> chem_id(i)), xa_orig(i), na_orig(i)
>          enddo
>          write(*,*) 'Sum(xa_orig) = ', sum(xa_orig(1:s% species))
>
>          deallocate(xa_orig, na_orig)
>
> 5. Let’s take a look at the numbers popping up on terminal. X_i is the
> abundance in mass fraction, and N_i is in number fraction
>
>     i  Name          X_i             N_i
>     1  h1            0.7381E+00      0.1200E+02
>     2  he3           0.2645E-04      0.7554E+01
>     3  he4           0.2485E+00      0.1153E+02
>     4  c12           0.2370E-02      0.9206E+01
>     5  n14           0.6943E-03      0.8496E+01
>     6  o16           0.5732E-02      0.9413E+01
>     7  o18           0.1293E-04      0.6642E+01
>     8  ne20          0.1165E-02      0.8420E+01
>     9  ne22          0.9423E-04      0.7261E+01
>    10  mg24          0.3331E-02      0.8751E+01
>  Sum(Xa) =   0.99999999999999989
>
> 6. As you see, the number fraction N_i for he4 is 11.53, which is supposed
> to be 10.93.
> This is the instant when a red alarm goes on in me :-D
>
> I would be glad to know if I made a mistake in my short script.
> Otherwise, I have to investigate deeper what’s going on. Is
> /star/private/adjust_xyz.f the first to blame?
> If not, where shall I start to spot the sinner? I would be glad to figure
> this out.
> I use v. 7116, and the whole work directory is attached.
>
> Thanks for your patience reading my long email through.
>
> Happy Sunday.
>
> Ehsan.
>
>
>
>
>
>
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>
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>


-- 
Pablo Marchant Campos
M.Sc on Astrophysics, Universidad Católica de Chile
PhD student, Argelander-Institut für Astronomie
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