[Mesa-users] Inquiry about Units in profile.data

[Guo Li]

Dear Diogo,

Thank you for your detailed explanation. I have verified that the unit of rate_r_c12_ag_o16 is indeed [gram/(mole.sec)]. I am currently testing the latest version of MESA, mesa-24.8.1.

I appreciate your insights and will keep your suggestions in mind as I proceed.

Best regards,
Guo Li
National Astronomical Observatories, CAS
















At 2025-02-20 05:28:56, "Diogo Capelo" <diogo.capelo at tecnico.ulisboa.pt> wrote:

Hi again,

In your case, and assuming the variable that is writing onto the profile column is reading "rate_screened",  the units of the rate_r_c12_ag_o16 would be indeed [gram/(mole.sec)]. The product of this with two molar fraction (y) factors, each with units of [mole/gram] gives [mole/(gram.sec)] which are the units of dy/dt = d[mole/gram]/dt : [mole/(gram.sec)].

If you're not obtaining the correct results, perhaps you're not multiplying the value of the screened rate by the molar fractions of the reactants (in your case, C12 and He4).

Unless there's a specific reason you need to be using that version of MESA, if you update to the current version, it's much easier to handle anything related to nuclear reaction rates (thanks devs!)

Hope this helps.

--

Diogo




A 2025-02-17 23:13, Guo Li escreveu:

Hi Meng and Diogo

 

Thank you for your guidance！

 

I am currently using MESA version r12778 and have modified the example from the test_suit, specifically based on the agb example. I have identified that the profile column 'log_rate_r_c12_ag_o16' is defined in the src/run_star_extras.f file.

My goal in examining the reaction rates is to calculate the timescales for specific reactions, such as the CNO cycle, and to compare them with the timescales for convective mixing. I have considered whether the appropriate units might be dy/dt (grams/(mole sec)), dn/dt (cm^-3/s), or simply the reaction rate units (cm^3/(mole sec)). However, my calculations have not yielded consistent results, and I have not found any documentation specifying the units for the profile column 'log_rate_r_c12_ag_o16'.

Any guidance or references would be greatly appreciated.

Best regards,
Guo Li
National Astronomical observatories,CAS

 

 

 

 

 

At 2025-02-17 18:13:16, "Diogo Capelo" <diogo.capelo at tecnico.ulisboa.pt> wrote:

Greetings,

That will depend on the version of MESA you're using. In the newer versions of MESA (23 and 24), the reaction rates you can output directly from profile_columns.list are in units of (s^-1). However, the default names of the columns don't match the one you use.

The name you use suggests to me (but I may be mistaken) that you are using an older version (pre-23) of MESA with a custom piece of code in run_star_extras to read out the reaction rates. In this case, the documentation on the "rate_screened" variable (which is the one likely being read and printed) is defined in "$MESA_DIR/net/public/net_def.f90", where you can read:

"The units here depend on the number of reactants. In all cases, the rate_screened times as many molar fractions as there are reactants gives a number with the same units as dy/dt. So for a 2body reaction, there are 2 Y factors, each with units [moles/gram] and the rate_screened units for such a reaction are [grams/(mole sec)], which when multiplied by [moles/gram]^2 gives the same units as dydt. For a 1body reaction (e.g., a decay), there is only 1 Y factor, so the units are [1/second]. Similarly, a 3body reaction will have rate_screened with units of [gram^2/(mole^2sec)]."

I would advise checking whether you're writing the rates into the profile directly or whether you're outputting them via run_star_extras and, in the latter case, checking which variable is being passed onto the profile, and then tracking down that variable in the MESA files.

Hope this helps!

--

Diogo

A 2025-02-17 09:25, Guo Li via Mesa-users escreveu:

Hi all,

I hope this message finds you well.

I am currently analyzing the profile.data file and would like to inquire about the units for the reaction rate column, such as log_rate_r_c12_ag_o16. 

Thank you for your support!

 
Best regards,
Guo Li
National Astronomical observatories,CAS
 


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