[mesa-users] Approx21

[Bill Paxton]

Hi Ian,

Let me make a try at answering.

On Oct 16, 2016, at 9:23 PM, Ian Foley wrote:
> 
> 1. In simulations up to Fe core collapse, the primary central isotope which remains at the end is cr56 which in my reading conflicts with research.

With big nets (over 150 isos), the burning will automatically find the final Ye at core collapse.
With the small approx nets, you have to help it out by selecting a "neutron dump" iso that gives the Ye you want.
The "cr56" option is only one of many options: cr56-cr66 and mn56-57 are all available.

> 2. There are some reactions which contain isotopes such as Fe53 and Fe55 which are not in the isotope list. This will not work for data files

The approx nets only follow the "main" isos and treat the others as in equilibrium.  For iron, we follow Fe52, Fe54, and Fe56 while assuming equilibrium Fe53 and Fe55.
I don't know what problems that might be causing for your data files.  Say more.

> 3. The isotope Na23 is missing. In intermediate stars, research shows the main ingredients of the degenerate cores are o16, Ne20, Na23 and Mg24.

We are not following Na23 abundances explicitly, but we do include reactions that have Na23 as an intermediate.
So adding Na23 is not likely to make a significant impact in that respect.
But of course if you are concerned about following the abundance of Na23 instead of having it assumed to be in equilibrium, then you need a net that includes it.
Frank and I were discussing this recently -- you might see if you can convince him to make it a priority.

> So I've been looking for ways to create a simple net which does not have a big performance hit, but gives results closer to research.

Closer in what ways?   Energy production?  Abundances of a larger set of isos?  Final Ye profile at collapse?
As I've mentioned, the approx nets focus on the 1st.  

I spent many months a couple of years ago looking for solutions to the other goals using hardwired nets similar to appox but with up to 40 isos.   I was trying to find a small net that could also derive Ye for itself rather than having it set by the choice of the neutron-dump iso such as Cr56, but I failed.  My current impression is that there is a sterile dessert between the under 30 iso approx nets and the over 150 iso big nets. 

Depending on your application, you might have better luck.   "Soft" nets are much easier to experiment with, but they require all the isotopes that are involved in relevant reactions.  There are some examples of my playing in mesa/data/net_data/nets/mesa_*.net, with mesa_45 being the smallest. 

> I also wanted to find a net which can simulate up to core collapse leading to electron capture supernovas. Are there any in mesa which can do this?

I'll leave that question to Josiah and Frank.  

Cheers,
Bill






> 
> Kind regards
> Ian
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