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

Roni Waldman roni181066 at gmail.com
Tue Jun 25 07:31:28 EDT 2013


Hi Tuguldur,
Exactly what I was thinking.
The RSG to BSG ratio might be a good thing to look at, although I don't
think it should give a very tight constraint.
Cheers,
Roni


On Tue, Jun 25, 2013 at 2:06 PM, Tuguldur Sukhbold <sukhbold at ucolick.org>wrote:

> Roni,
>
> I highly doubt if somebody will be able to tell you a nice set of values
> that are applicable for various scenarios. As mentioned by these people,
> the set of "f" values will change probably a lot depending on what you're
> specifically trying to do, and probably you need to be creative yourself in
> order to justify your choice. Let's say you're trying to do core He burning
> in massive stars, then one method coming to my mind is to figure out the
> amount that doesn't directly contradict with the observed RGB and BSG
> ratio...
>
> People have been trying to measure the overshooting through a single
> parameter using eclipsing binaries, open clusters, apsidal motion studies
> etc and more recently with asteroseismology. The results from all these
> works look more like a scatter plot rather than a nice relation, even for
> the 'simpler' case of main sequence core overshooting.
>
> Tuguldur
>
>
>
>
>
> On Jun 25, 2013, at 3:39 AM, Roni Waldman <roni181066 at gmail.com> wrote:
>
> 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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