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

Roni Waldman roni181066 at gmail.com
Tue Jun 25 08:40:45 EDT 2013


Hi Stan,

Also, there is evidence that core collapse supernovae happen
> for masses as low as 8 Msun. It is my impression that without overshoot
> MESA gives a much higher threshold. It also gives different preSN
> luminosities
> (lower) than either the Geneva or UCSC group.
>
> As far as I understand, Kepler gives a threshold of 9 Msun for CCSN (I
take this from the comparison in Poelarends+ 2008).
Recent paper by Jones+ 2013 shows a CCSN for 9.5 Msun with overshoot, and
an ECSN for 8.8 Msun, so the threshold is somewhere in between.

With the same overshoot parameters, I get with MESA the same preSN
luminosities as the Geneva results.
Haven't done detailed comparison with UCSC results.

Roni



>
> On Jun 25, 2013, at 1:31 PM, Roni Waldman <roni181066 at gmail.com> wrote:
>
> 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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