[mesa-users] Asplund abundances in MESA -- which ones?

Richard Townsend townsend at astro.wisc.edu
Wed Apr 15 12:04:13 EDT 2015


> On Apr 15, 2015, at 10:07 AM, Richard Townsend <townsend at astro.wisc.edu> wrote:
> 
> Thanks for the info!
> 
> So, can people comment on what is ‘best-practice’ for generating MESA models for Pop I stars? I guess a first stab would be to use the ‘AGSS09’ set but rescale hydrogen/helium/all metals using the proto-solar X, Y and Z given by Asplund+09. But is there a better way to do this?
> 

Having now read Asplund+09 more closely, I see that their proto-solar values are derived from the solar photosphere values by rescaling all metals (relative to H) by 0.04 dex. So, in MESA, all that’s necessary to achieve proto-solar Asplund+09 abundances is to use the ‘AGSS09’ mixture together with X=0.7154, Y=0.2703 and Z=0.0142 (based on the last row of table 4 of Asplund+09). 

cheers,

Rich

> cheers,
> 
> Rich
> 
>> On Apr 15, 2015, at 9:58 AM, Stan Woosley <woosley at ucolick.org <mailto:woosley at ucolick.org>> wrote:
>> 
>> Unless you are explicitly interested in modeling the current solar convection zone, the abundance of Li
>> there is useless. It has been depleted orders of magnitude by nuclear reactions at the base of the convection
>> zone. The meteoritic value - from primitive C1 carbonaceous meteorites - reflects the composition of the 
>> primordial solar nebula.
>> 
>> Also, if you are interested in solar composition as a representation of initial Pop I material
>> in making a star model, or as a target for nucleosynthesis studies, you should use the corrected
>> protosolar abundances not the current solar photospheric ones. Diffusion out of the convection
>> zone has changed the abundance of everything, including H and He. I recall the change in 
>> heavy elements as being 0.05 dex.
>> 
>> Lodders (2009) has a similar - and for me - equally useful solar and zero age solar abundance set.
>> 
>> Reading wither of their papers gives background on the uncertainties in each element.
>> 
>> Stan
>> 
>> 
>> 
>> On Apr 15, 2015, at 6:20 AM, Richard Townsend <townsend at astro.wisc.edu <mailto:townsend at astro.wisc.edu>> wrote:
>> 
>>> Thanks, Jieun!
>>> 
>>> Comparing the data in chem_def.f90 against Table 1 of Asplund+09, it looks like the meteoritic values for As, Se and Br are used in the file because the photosphere values are missing.
>>> 
>>> However, that doesn’t explain why the meteoritic value for Li is used, rather than the photosphere value. Does anyone have any ideas?
>>> 
>>> cheers,
>>> 
>>> Rich
>>> 
>>>> On Apr 14, 2015, at 9:52 PM, Choi, Jieun <jieun.choi at cfa.harvard.edu <mailto:jieun.choi at cfa.harvard.edu>> wrote:
>>>> 
>>>> Hi Rich,
>>>> 
>>>> Comparing Table 1 in Asplund+09 and the log abundances listed in init_AGSS09_data, it looks like MESA's using present-day photosphere values with a few exceptions, e.g., Li, Br.
>>>> 
>>>> Cheers,
>>>> Jieun
>>>> 
>>>> On Tue, Apr 14, 2015 at 9:37 PM, Richard Townsend <townsend at astro.wisc.edu <mailto:townsend at astro.wisc.edu>> wrote:
>>>> Hi folks —
>>>> 
>>>> In chem/chem_def.f90, the ‘AGSS09' abundances are referenced as coming from Asplund, Grevesse, Sauval, and Scott 2009 (Annu. Rev. Astron. Astrophys. 2009. 47:481–522). But Asplund et al give values for both solar and proto-solar abundances. Which is MESA using?
>>>> 
>>>> cheers,
>>>> 
>>>> Rich
>>>> 
>>>> 
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