[mesa-users] Fwd: 35Cl and K39

[David Arnett]

On Mon, Jun 4, 2012 at 12:30 PM, Roni Waldman <roni181066 at gmail.com> wrote:

> Hi Dave,****
>
> I begin to understand the network problem.
>

Great!


> ****
>
> I’ve also experimented in MESA with a network devised with the help of Jim
> Truran for SN explosive burning (attached).
>

Thanks for sending it, and see below.

****
>
> In this case I got stuck with an excess of Si30, S34 and so on. Do you
> have an idea why?
>

Probably real? You have enough nuclei to get that right.  K40, K41 might
help, and I would
wonder about the bottleneck to the Fe peak (is it by n-capture or do you
have high enough
T for charged-particle links to be open?). Otherwise it seems plausible.

> ****
>
> ** **
>
> Why exactly is mixing a problem, wouldn’t mesa automatically do the mixing
> for all species in the set? Or is it just a matter of time consumption?
>

The problem is  physics. Mixing length theory is local and steady state,
stellar convection is
intermittent, turbulent, and nonlocal (Newton's laws of motion). There
should be a turbulent
boundary layer, which MLT never can give. Look at ADS for papers by Casey
Meakin and me :-)

****
>
> For my interest, do you have a list of species and reactions for the 81
> and 177 networks that you can send me?
>

Attached. My code automagically adds all the reaction links from the JINA
database for
the nuclei requested.

Dave


> ****
>
> Roni****
>
> ** **
>
> *From:* David Arnett [mailto:wdarnett at gmail.com]
> *Sent:* יום ב 04 יוני 2012 22:02
> *To:* Bill Paxton; mesa-users at lists.sourceforge.net
> *Subject:* [mesa-users] Fwd: 35Cl and K39****
>
> ** **
>
> ** **
>
> ---------- 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****
>



-- 
David Arnett
Regents Professor
Steward Observatory
University of Arizona
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