[Mesa-users] Individual Chemical Abundances by number

Francis Timmes fxt44 at mac.com
Sat Oct 10 16:49:50 EDT 2020

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 

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.

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.


> 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
> _______________________________________________
> mesa-users at lists.mesastar.org
> https://lists.mesastar.org/mailman/listinfo/mesa-users

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