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

[Ehsan Moravveji]

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.




-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.mesastar.org/pipermail/mesa-users/attachments/20141102/bdc2d2db/attachment.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: test-A09-Xa.zip
Type: application/zip
Size: 26265 bytes
Desc: not available
URL: <https://lists.mesastar.org/pipermail/mesa-users/attachments/20141102/bdc2d2db/attachment.zip>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.mesastar.org/pipermail/mesa-users/attachments/20141102/bdc2d2db/attachment-0001.html>