[Mesa-users] BD deuterium burning

[Bear Ealeal]

Dear Jaredand Matías,

Thank you very much for your answers.

What I did is, I enabled the initialcomposition (the net was already ok) to:

set_uniform_initial_composition= .true.

                              initial_h1  = 0.70

                              initial_h2  = 2d-5

                              initial_he3 = 1d-5

                              initial_he4 = 0.28
and now I getan increase in He3 and a decrease in h2, in the center, however the center temperatureis still about logT_c \approx 5.3, which surprises me since  I expected it to be 10^6K.
The raw_rate_r_h2_pg_he3is between 10^27  - 10^32 reactions / (g·s).  The value of raw_rate_r_h2_pg_he3 increases up to 10^32 andthen decreases.

Do you knowif these values are indicative to deuterium burning?  I do not think I  have deuteriumburn because of the center T.  I will tryto play with the initial composition but any other suggestions will be great.

Thank youvery much,

Ealeal



 

    On Wednesday, August 6, 2025 at 11:40:49 PM GMT+3, Jared Goldberg <jgoldberg at flatironinstitute.org> wrote:  
 
 By default, MESA uses a very simplistic nuclear reaction network called "basic.net" which does not include deuterium or its burning pathways. (See https://docs.mesastar.org/en/latest/net/nets.html)
Even when using a network including deuterium, it does not initialize stars with any deuterium by default, so you will need to explicitly set the initial abundances including deuterium, in addition to making sure that your nuclear reaction network contains deuterium burning. 
In practice, this means that in the &star_job section of your inlist, you will want to switch to a net that includes the appropriate reactions, for example: 

change_net = .true.
change_initial_net = .true.
new_net_name = 'pp_and_cno_extras.net'

You will then need to add deuterium by setting the initial composition or relaxing the composition, e.g. 

set_uniform_initial_composition = .true. (documentation: https://docs.mesastar.org/en/latest/reference/star_job.html#set-uniform-initial-composition)
initial_h2 = 1d-5 ! or however much deuterium you want

and set the other initial abundances and abundance ratios as desired. 
Cheers,~Jared


On Wed, Aug 6, 2025 at 2:13 PM Matias Jones via Mesa-users <mesa-users at lists.mesastar.org> wrote:


Hi Ealeal,




Probably you need to modify the default rate_list.txt file (I guess is under data/rates_data/rate_tables/ dir) to include D burning. This worked for me.

I am using an older MESA version, but probably this is also the case for v23.5.1.







Cheers, 




--------------------------------------------------------------------
Dr. Matías Jones F.
VLT Operations Staff Astronomer
ESPRESSO Instrument Scientist SPHERE Instrument Scientist (IS2)European Southern Observatory
Alonso de Córdova 3107, Vitacura, Santiago, Chile
--------------------------------------------------------------------De: Mesa-users <mesa-users-bounces at lists.mesastar.org> en nombre de Bear Ealeal via Mesa-users <mesa-users at lists.mesastar.org>
Enviado: miércoles, 6 de agosto de 2025 12:26:50
Para: mesa-users at lists.mesastar.org
Asunto: [Mesa-users] BD deuterium burning 
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Dear Mesa-users,

I am working on MESA 23.5.1 and I run the example from test -suite named: "make_brown_dwarf" with no changes.

mass and radius are:

mass_in_gm_for_create_initial_model = 1.9892d31 ! 0.01 Msun; m_jupiter = 1.8986d30; msun = 1.9892d33

   radius_in_cm_for_create_initial_model = 3.5d10 ! 5 r_jupiter; r_jupiter = 6.9911d9. ok for most brown dwarfs.
The age when the inilist stops is 2Gyr. 
However, I do not get deuterium burning although I getraw_rate_r_h2_pg_he3 up to 1e18, the temperature at the center is too low also and there is no increase even not in the core in He3.Does someone have experience with BD in MESA, especially how to make the deuterium burn ?
Thanks,

Ealeal

 

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