[Mesa-users] A question about MESA for pre-main-sequence evolution

Sat Oct 22 15:14:12 UTC 2022

Hi Meridith and mesa-users,

Thanks for you reply. But There still seem to be some problems. I found that even though I added deuterium to the calculation, the calculation was the same as before.

We want to calculate M=0.2 M_sun evolutionary trajectory with metal abundance Z=0.019, Helium abundance Y=0.275 . Let me just show you my configuration file and output briefly(See attachment for the complete configuration file(code)). I choose the $MESA_DIR$/star/test_suite/make_zams_low_mass for template.

1) changes M_sun, Y and Z from template
code:
"
Zbase = 0.019d0
"
in inlist_zams, &kap, and
"
initial_mass = 0.2d0
initial_z = 0.019d0
initial_y = 0.275d0

" in inlist_zams, &controls.

The output trajectory is:

2) Changes M_sun Y Z from template. Set deuterium abundance to 2e-5. Set Nuclear reaction networks to h_burn.net. Following your advice to set "pre_ms_relax_to_start_radiative_core = .false."
code:
"
pre_ms_relax_to_start_radiative_core = .false.
set_abundance = .true.
set_initial_abundance=.true.
chem_name = 'h2'
new_frac = 2e-5
"
in inlist_zams, &star_job
"
Zbase = 0.019d0
"
in inlist_zams, &kap, and
"
initial_mass = 0.2d0
initial_z = 0.019d0
initial_y = 0.275d0

" in inlist_zams, &controls.

The output trajectory is:

The results of the two simulations are very similar, but different from Fig. 15 in paper Modules for Experiments in Stellar Astrophysics (MESA) 2010. This picture is shown following.

a) The shape of the trajectory is not quite the same as the trajectory on the paper.
b) The ending of the evolution is different. For example, the ending of the 0.2 M_sun trajectory in my results, Log Teff=3.55, the ending of the 0.2 M_sun in paper's results, Log Teff < 3.525.

It seems that the nuclear reaction does not affect the trajectory and ending too much? Is there something I haven't considered. Sorry, I just started mesa. Would you please give me some suggestions for this problem. Thanks you a lot.

Thanks
LiJiaxun

-----原始邮件-----
发件人:"Meridith Joyce" <meridith.joyce at gmail.com>
发送时间:2022-10-20 22:50:29 (星期四)
收件人: lijiaxun at mail.ustc.edu.cn
抄送: mesa-users at lists.mesastar.org
主题: Re: [Mesa-users] A question about MESA for pre-main-sequence evolution

Hi LiJiaxun,

My recommendations come from an inlist I used with version 15140 (meaning some things might be different from your version):

Have a look at the &star_job controls. I have the following configuration for setting deuterium:

      set_abundance = .true. 
      set_initial_abundance = .true. 
      chem_name = 'h2' 
      new_frac = 2e-5 

For pre-main sequence evolution of low-mass stars, it is also important to set
    pre_ms_relax_to_start_radiative_core = .false.

Also ensure that deuterium is included in the nuclear network you use. 

In my opinion, it is also better to set your hydrogen and helium abundances with &star_job parameters rather than &controls parameters. Setting Zbase in &kap to your Z value
Z = 1 - (X + Y + deuterium etc ) 
is generally safe.

Hope that helps,

On Thu, Oct 20, 2022 at 4:35 PM LiJiaxun via Mesa-users <mesa-users at lists.mesastar.org> wrote:

Hi,
My name is Li Jiaxun. I am a student who have just started to learn MESA. I want to calculate low mass pre-main-sequence star to main-sequence. So I choose the $MESA_DIR$/star/test_suite/make_zams_low_mass for template. 
In order to calculate metal abundance Z=0.019, Helium abundance Y=0.275 and M=0.085 M_sun or M=0.2 M_sun, I only changed the following Settings
"
Zbase = 0.019d0
"
in inlist_zams, &kap, and
"
initial_mass = 0.085 !or 0.2
initial_z = 0.019d0
initial_y = 0.275

" in inlist_zams, &controls.
The following two pictures are results of 0.085 and 0.2 M_sun.
--------------------------------------------------M = 0.085 M_sun-----------------------------------------------------------

-------------------------------------------------M = 0.2 M_sun--------------------------------------------------------------

Their trajectories on HRD are much different from Fig. 15 in paper Modules for Experiments in Stellar Astrophysics (MESA) 2010. This firgure is displayed following

We can see that:
1) The shape of the trajectory is not quite the same as the trajectory on the paper.
2) The ending of the evolution is different. For example, the ending of the 0.2 M_sun trajectory in my results, Log Teff=3.55, the ending of the 0.2 M_sun in paper's results, Log Teff < 3.525. 
The calculation is so different. After reading paper, I realized that maybe I hadn't considered deuterium and lithium burning, so I checked out the output file and found that deuterium and lithium had been zero throughout the evolution. So how do I set the initial elements in mesa? Because it seems like I can only set the abundances of H, He, and metals, but not the abundances of deuterium, the isotope of H.
Faced with the above problems, I hope to get your help. Would you please offer me some advice on?  Thanks you a lot.

Thanks!
LiJiaxun
_______________________________________________
mesa-users at lists.mesastar.org
https://lists.mesastar.org/mailman/listinfo/mesa-users

--

Dr Meridith Joyce 
Marie Sklodowska-Curie Actions Widening Fellow
CSFK Konkoly Observatory, Budapest, Hungary 1121
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