[Mesa-users] modelling a pure h1 surface star

[Biswas, Anwesha [PHYSA]]

Hi Morgan,

The reason I wanted to accrete hydrogen is I am studying pulsations in DAVs and any impurities of other elements will affect the temperature range of the cooler edge.
When I am printing out the fraction of elements in the outermost cell (index 0) after cooling it in wd_cool_0.6M test case, the mass fracture of h1 at index 0 is not 1. It has some amount of (of order 1e-16) he3,he4,c12,n14,o16,o18,ne20,ne22,mg24,si28
the diffusion is turned on.
I wanted h1 to be 1 and everything else to be 0 at the outermost part. That's why I was thinking maybe accreting h1 would be a better option to achieve this.
I am at version r23.05.1 but it hasn't changed much from r22.05.1 at least for my purposes.
Thank you for all the help.. Also I would try to get a thinner envelope (so making those changes will be beneficial too). I will try them

Anwesha
________________________________
From: Morgan Taylor <taylormorgan32 at gmail.com>
Sent: Sunday, August 6, 2023 17:12
To: Biswas, Anwesha [PHYSA] <anwesha at iastate.edu>
Cc: mesa-users at lists.mesastar.org <mesa-users at lists.mesastar.org>
Subject: Re: [Mesa-users] modelling a pure h1 surface star

Hi Anwesha,

If I understand right, the  'inlist_remove_env' will end up giving you a final pure hydrogen envelope of 10^(-4) Msun for the default 0.6 Msun WD.  Is your desired envelope mass less than or greater than this?  Or are you wanting to do both?

If it is less, you could try using these to star_job controls in 'inlist_settle':
(copied and pasted from the $MESA_DIR/star/defaults/star_job.defaults file)

   ! relax_mass_to_remove_H_env
      ! ~~~~~~~~~~~~~~~~~~~~~~~~~~
      ! relax_initial_mass_to_remove_H_env
      ! ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      ! extra_mass_retained_by_remove_H_env
      ! ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

      ! Gradually reduce total mass by a wind to remove the H envelope.
      ! Equivalent to relax_mass with new_mass = He_core_mass + extra_mass.
      ! ::
    relax_mass_to_remove_H_env = .false.
    relax_initial_mass_to_remove_H_env = .false.
    extra_mass_retained_by_remove_H_env = 5d-3 ! (Msun)

Here, change the default relax controls to .true., and change the extra mass control to your desired hydrogen envelope mass.  This way, you might be able to avoid removing the envelope completely and then accreting.  Might be as simple as just shaving off a bit more after inlist_remove_env does most the work for you ;)

If you still want to accrete more mass after taking the H envelope off completely, or want more than the default 10^-4 Msun mass the code defaults to, perhaps you could utilize x_ctrl(2) in 'inlist_settle'.  So do the procedure you described.  Then use x_ctrl(2) to help you know when to stop accreting.
Something like x_ctrl(2) = <desired H_env_mass>.  Then in run_star_extras, in the extras finish step function, write something that checks if the s% envelop_mass <= s% x_ctrl(2).  If it is, change s% accrete_given_mass_fractions to .false.  The evolution should then stop accreting mass to the hydrogen envelope.

For a final termination condition to reach the red edge, I recommend using

Teff_lower_limit = 11,000

in the controls of 'inlist_settle'. (Or a lower Teff if you want to evolve slightly further.)

 Another option for your overall project is to use wd_builder, which I'd be happy to tell you more about if you are interested.

p.s. I was looking at the test suite from mesa 22051.  I assume they hold for the latest mesa version, but i apologize in advance if I'm wrong.

Hope this helps,
Morgan

On Sat, Aug 5, 2023 at 4:56 PM Biswas, Anwesha [PHYSA] via Mesa-users <mesa-users at lists.mesastar.org<mailto:mesa-users at lists.mesastar.org>> wrote:
Hi,

I am trying to model a pure hydrogen envelope white dwarf to match with the observations of pulsating DAVs (target Teff 13k [K] to 10k [K]). I am looking around 11,000[K]

I am using make_co_wd to evolve one. However I am trying to remove the hydrogen envelope completely. I have set
--> x_ctrl(1) = 0 (inlist remove envelope)
and made a change in run_star_extras.f90
--> (s% m(k) > bottom_mass)  and then cut it there so that the mass of star is the bottom mass
for this reason.

 Now I want to add on a very thin layer of pure hydrogen to the surface which might be done by the following
-->accrete_same_as_surface = .false.
-->accrete_given_mass_fractions = .true.
-->num_accretion_species = 1
-->accretion_species_id(1) = 'h1'
-->accretion_species_xa(1) = 1.0
-->mass_change = 5d-9 !Msun/year

Now I am a bit lost regarding which inlist to add this into 'make_co_wd' so that after removing the original envelope, I can add that and what will be the termination string in that case. I am trying to study pulsation at the red edge around 11000[K]


Anwesha

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

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.mesastar.org/pipermail/mesa-users/attachments/20230806/a7d0dbf0/attachment.htm>