[mesa-users] wd diffusion

[Jing Luan]

Hi Bill,

Thank you very much :-) One more question please? Since the current wd
models that I know in mesa already have total hydrogen mass ~ 10^(-4)*M_wd.
Do you have a model with total H <<10^(-4)*M_wd please? Thank you :-)

Sincerely,
Jing

On Mon, Jan 9, 2017 at 11:10 AM, Bill Paxton <paxton at kitp.ucsb.edu> wrote:

>
> On Jan 9, 2017, at 11:03 AM, Jing Luan wrote:
>
>  A pure hydrogen atmosphere would be good enough.
>
>
> Good to know.  My advice is forget about diffusion for now and try adding
> pure H to the surface of an existing model by accretion.
>
> something like this with whatever accretion rate you can get away with --
> try increasing until run into problems.
>
>       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 = 1d-9 ! rate of accretion (Msun/year)
>
> The H should stay at the surface unless there is convection reaching it.
>
> There are lots of folks on mesa-users who can help with this -- Rob is a
> hero, but we don't want to overwork him too much!  ;)
>
> -b
>
>
>
>
> Since I am studying wd's oscillation, the H-He transition would affect a
> little the eigen frequencies, so it would be better if I have the H-He
> transition. The hydrogen atm's mass is about 10^(-4) of the wd's mass.
> M_{wd} = 0.6Msun. Teff ranges from 13000 to 9000, covering the instability
> strip for DAVs.
>
> Many thanks!
>
> Sincerely,
> Jing
>
> On Mon, Jan 9, 2017 at 10:35 AM, Bill Paxton <paxton at kitp.ucsb.edu> wrote:
>
>> it would also be good to clarify your goals -- are you studying
>> diffusion, or is diffusion just a way to create models for the topic you
>> are actually interested in?  if the latter, then there may be other ways to
>> create models for you with a pure H outer shell that use "stellar
>> engineering" instead of diffusion.
>>
>> b
>>
>>
>> On Jan 9, 2017, at 10:19 AM, Robert Farmer wrote:
>>
>> Hi
>> Have you tried the wd_diffusion and/or the wd_surf_at_tau_1m4  test_suite
>> cases?
>>
>> If you have and are still having problems, can you post your inlists with
>> the changes you've made.
>>
>> Regards
>> Rob
>>
>> On Sun, Jan 8, 2017 at 4:55 PM, Jing Luan <jingluan.xw at gmail.com> wrote:
>>
>>> Hello,
>>>
>>> I'd like to make a WD model with pure hydrogen atmosphere, i.e. all
>>> heavier elements have settled down. Thus I turn on diffusion in mesa.
>>> However, mesa has a hard time converging when I also require the surface
>>> optical depth to be 5 or even lower (actually I need the low optical depth
>>> part to be treated well in the model). Does anyone know that why diffusion
>>> does not work well in low optical depth part please? Or how do I get a WD
>>> model with hydrogen, helium and metals well separated in depth while its
>>> surface goes up to tau=0.01 please?
>>>
>>> Many thanks!
>>>
>>> Sincerely,
>>> Jing
>>>
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>
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