[mesa-users] wd diffusion

[Bill Paxton]

I'm going to let other mesa-users come forward to take over helping you now. 

good luck,
b




On Jan 9, 2017, at 11:41 AM, Jing Luan wrote:

> 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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