[Mesa-users] Individual Chemical Abundances by number

[Francis Timmes]

baryon number is an invariant under nuclear reactions.
so, define the abundance of species Y_i by

Y_i = N_i / N_b = n_i / n_b 

where 
N_i is the number of nucleons of isotope i,
N_b is the total number of baryons, 
n_i is the number density (1/cm^3) of nucleons of isotope i, and
n_b is the total number density (1/cm^3) of baryons.

The number of baryons in isotope i (N_i * A_i) divided by the 
total number of baryons N_b is the baryon fraction 

X_i = N_i * A_i / N_b = Y_i * A_i 

where A_i is the atomic number of isotope i.
sometimes the baryon fraction is called the mass fraction.
note 

sum X_i = N_b / N_b = 1 .

define the baryon density (g/cm^3) as

rho_b = n_b * m_amu

where m_amu is the atomic mass unit (in g). 
sometimes the baryon density is called the mass density rho.

you can likely take it from here to get what you want.

fxt





> On Oct 10, 2020, at 12:38 PM, Trust Otto via Mesa-users <mesa-users at lists.mesastar.org> wrote:
> 
> Dear MESA users,
> 
> I am using MESA-version 12778 and interested in obtaining individual chemical abundances (from H to Ni) by number for 1.6 to 3.0 Msun MS stars. The individual chemical abundances I managed to get after editing the history_columns.list and profile_columns.list files and choosing an appropriate net are mass fractions. How can I get the individual chemical abundances by number?
> 
> Thank you in advance.
> 
> ----------------------------------------
> Otto Trust
> 
> Department of Physics
> Mbarara University of Science and Technology
> P.O.Box 1410
> Mbarara-Uganda
> Tel:+256-785-521069/757-650945
> e-mails: trust.otto at yahoo.com/otrust at must.ac.ug
> 
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