[mesa-users] Fwd: 35Cl and K39

[David Arnett]

---------- Forwarded message ----------
From: David Arnett <wdarnett at gmail.com>
Date: Mon, Jun 4, 2012 at 12:00 PM
Subject: Re: 35Cl and K39
To: Roni Waldman <roni181066 at gmail.com>


Hi Roni,

On Mon, Jun 4, 2012 at 11:38 AM, Roni Waldman <roni181066 at gmail.com> wrote:

> Hi Dave,****
>
> I used the ns_he.net which was provided with MESA.
>
Thanks. It sounded familiar.

> ****
>
> I just naively supposed it has been tested by someone who devised it.
>
It certainly has been tested (Bill Paxton is good and careful), but maybe
not for your problem.

> ****
>
> I attach a file containing the list of nuclei and reactions in the net.***
> *
>
> ** **
>
> Let me clarify, if you are saying that for Si burning you need ~60
> isotopes, then do you mean that the approx21 network which is standard in
> MESA (see attached file) is also wrong?
>
Yes, in general. No, if you are doing the problem it was devised for.


> ****
>
> It was my understanding that it is possible to devise small effective
> networks which give the energy production correctly, without getting stuck
> into an unrealistic composition.
>
This is an art rather than a science. The network you sent, ns_he.txt,
will have trouble if the neutron excess deviates much from .002 because you
have no Si30 or S34, which sop up extra neutrons. If they are missing,
these neutrons glom onto CL35 and K39, which have an extra neutron
(Z=17,N=18, e.g.). Because odd Z elements are rare, this gives a big effect
in the ELEMENTAL abundance.
However, the energy generation is probably well represented because the
binding energy of  these nuclei is about the same as those omitted :-)
In TYCHO, my default was 81 nuclei, a compromise which got the elemental
abundances about right. I am using 177 for core collapse.
I am working with Bill and the MESA team to implement a large network
option in MESA. The problem is getting the mixing right, which is not now
done by anyone. Bill has a version that puts the network inside the Henyey
sweep, but it becomes slow for reasonable networks. I have a big network,
but my coupling of "chemistry", that is, burning and evolution is operator
split.
I hope this helps.
Dave

>  ****
>
> Am I wrong?****
>
> ** **
>
> Thanks for your help.****
>
> Roni****
>
> ** **
>
> *From:* David Arnett [mailto:wdarnett at gmail.com]
> *Sent:* יום ב 04 יוני 2012 20:21
> *To:* roni181066 at gmail.com
> *Subject:* 35Cl and K39****
>
> ** **
>
> Hi Roni,****
>
> It depends on your network (which was removed from the email post, so I
> can't see it).  How may nuclei do you have? For Si burning you need ~60***
> *
>
> as a rule, to get the quasi-equilibrium right. With fewer, mass goes to
> strange places because of constraints on charge and nucleon number.****
>
> Maybe you should send more info offline.****
>
> Dave
> ****
>
> ** **
>
> --
> David Arnett
> Regents Professor
> Steward Observatory
> University of Arizona****
>



-- 
David Arnett
Regents Professor
Steward Observatory
University of Arizona



-- 
David Arnett
Regents Professor
Steward Observatory
University of Arizona
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