[mesa-users] overshoot_f_above_nonburn/burn_he/...

[Roni Waldman]

Hi Umberto,


Yes, you are right. As I also said to Ilka the parametrization depends on
> the specific model to compute.
> Concerning the lower value of f=0.008 recommended for He convective
> zones: is recommended to correctly reproduce the surface abundance of
> H-deficent post-AGB stars, i.e. stars that have lost their envelope through
> intense winds and show as surface abundances what were before He-intershell
> abundances. Surface abundances of such stars have been observed and
> published in papers like Werner et al 2007 and Werner et al 2009.. where
> specific range of He4, C12 and O16 are given, thus giving another strong
> observational constraint. A lower value of f is necessary in reproduce such
> abundances.
>

Can you point me to any reference calibrating  f=0.008 to the observational
results of Werner et al?
And again, this result is only relevant for AGB He shells flashes, not for
e.g. He core burning.

Cheers,
Roni

>
>  ------------------------------
> *From:* Roni Waldman [roni181066 at gmail.com]
> *Sent:* Tuesday, June 25, 2013 11:14 AM
> *To:* Umberto Battino
> *Subject:* Re: [mesa-users] overshoot_f_above_nonburn/burn_he/...
>
>   Hi Umberto,
>
>
>   overshooting parameters are also constrained by hydrodinamical 3D
>> simulations (e.g. Freytag et al. 1996, Herwig 2007 etc...).. I can tell you
>> something for low/intermediate mass stars.. where a classic setting is
>> given by setting f=0.014 to all the boundaries, except for the helium ones,
>> where a lower value is recommended (f=0.008). Consider these just as
>> indicative values, then it depends much more on the specific model you want
>> to compute.. for example during the so called "Third dredge up" events
>> during the AGB phase the f value under the hydrogen convective envelope is
>> generally multiplied by a factor of 9 using the inlist command
>> "overshoot_below_noburn_factor".
>> Check  also Herwig 2000 paper for more details! (Astron. Astrophys. 360,
>> 952–968 (2000)). This will surely be useful.. :)
>>
>
>  These are indeed very interesting papers regarding this subject.
> One has to keep in mind, however, that these are results valid for
> specific cases, e.g. the Herwig 2007 paper deals with He shell flashes in
> AGB stars, and shows different behavior in the upper and lower boundaries
> of the convective zone. This already points out the fact that there is no
> reason to assume the same overshoot parameter would apply for let's say He
> core burning. Also the authors point out there is a numerical uncertainty
> in the results of a factor of a few.
>
>  On what basis do you say that a lower value of f=0.008 is recommended
> for He convective zones?
>
>  Cheers,
> Roni
>
>>
>>
>>
>>  ------------------------------
>> *From:* Roni Waldman [roni181066 at gmail.com]
>> *Sent:* Tuesday, June 25, 2013 8:59 AM
>> *To:* Ilka Petermann
>> *Cc:* mesa-users
>> *Subject:* Re: [mesa-users] overshoot_f_above_nonburn/burn_he/...
>>
>>    Hi Ilka and MESA users,
>> As far as I know, the only observational evidence is that which you
>> mention, and it is relevant for the main sequence, i.e. overshoot above the
>> H burning core.
>> People usually use the same parameters for all other convective regions
>> just because there is no better thing to do.
>> If anybody knows otherwise, I will be happy to be corrected.
>> Cheers,
>> Roni
>>
>>
>> On Mon, Jun 24, 2013 at 10:44 PM, Ilka Petermann <m.ilka at gmx.de> wrote:
>>
>>>  Dear MESA users,
>>> I want to implement overshooting in my calculations and have a question
>>> about the MESA parameters describing it.
>>> If I understood correctly, a value for overshooting (e.g.
>>> overshoot_f_above_burn_h) is adjusted to match the width of the main
>>> sequence or to fit properties determined by asteroseismology,...
>>> However, there are also parameters for
>>> overshoot_f_above_nonburn/burn_he/burn_z? Is there a 'common recipe' to
>>> assign values to these?
>>> Thanks!
>>> Ilka
>>>
>>>
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>>
>
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