[mesa-users] Fwd: semiconvection (typo)

[Chris Mankovich]

Hey T,

I can tell you that you don't need to bother with any controls beyond
enabling Ledoux and setting an alpha_sc.  The form for the composition
gradient term "brunt B" now implemented in mesa by default can be found in
the second instrument paper. I have no experience running massive stars
with semiconvection, but in general for inefficient semiconvection (the
limit of which is pure Ledoux) you can get quite small cores.  I don't know
that anyone has done the comparison with Langer 1985 for specific alpha
values.

Chris
On Mar 31, 2013 2:06 PM, "Tuguldur Sukhbold" <sukhbold at ucolick.org> wrote:

> Dear MESA users,
>
> just noticed that I said following backwards in my yesterday's email:
>
> For example, it would be really hard to explode 1.d-3 model, as the CO
> core is too tiny, even 1.d-1 case is still very degenerate.
>
>
> I meant to say the opposite, too easy to explode. Basically I wanted to
> say that all of these 15Msun cases are developing really degenerate cores
> that one would 'usually' expect at much lower mass (~maybe around 10Msun or
> so). Sorry I was writing at 4am in the morning ;-)
>
> Tuguldur
>
>
>
>
>
>
> Begin forwarded message:
>
> *From: *Tuguldur Sukhbold <sukhbold at ucolick.org>
> *Subject: **semiconvection*
> *Date: *March 31, 2013 4:12:51 AM PDT
> *To: *"mesa-users at lists.sourceforge.net" <mesa-users at lists.sourceforge.net
> >
> *Cc: *Stan Woosley <woosley at ucolick.org>
>
> Dear MESA users,
>
> I have a sort of general questions about setting up the semi-convection in
> MESA. I would be very grateful if anybody shares their experience using it
> *especially* on massive stars.
>
> 1) According to star/defaults/controls.defaults, we only need these two in
> our controls:
>
> use_Ledoux_criterion = .true
> alpha_semiconvection = some value
>
> is this really it? am asking this because I have found this document on
> the forum:
>
>
> http://mesastar.org/documentation/tutorials/zams-test-cases/semiconvection/view
>
> here it mentions these two extra lines:
>
> use_gradmu_alt_for_mlt = .true
> radL_comp_term_logRho_switch = 3
>
> says it is used to control computations of 'certain' gradients. I couldn't
> find any information on these in my version (4798), probably because this
> document is made for 4299..? Here I just want to make sure that I am not
> missing anything in the setup.
>
> 2) Now more importantly, what is the value of some value? According to
> the control.defaults:
>
> alpha_semiconvection = 0 ! 0.01 ! determines efficiency of semi convective
> mixing
>
> but I remember in previous versions of the code (and also in the document
> mentioned above) it used to claim that 1.d-3 is a typical value. Can
> someone tell me where exactly these numbers are coming from? If one checks
> the actual Langer's paper:
>
> http://adsabs.harvard.edu/full/1985A%26A...145..179L<http://adsabs.harvard.edu/full/1985A&A...145..179L>
>
> it says the value is more like 0.1 (see section 3).
>
> Attached figure shows the result of a quick survey I did in the past
> couple of hours. I took 15Msun models and run it from ZAMS until when the
> central temperature reached T_c=5.d8K, this is roughly the condition when
> the carbon starts igniting in the center. I have calculated the same model
> with bunch of different values of alpha_semiconvection [0.00001-100]
> (anything over 1 is crazy), plus the same model with just pure
> Schwarzschild criterion. In all figures dashed curve/line represent result
> from this pure Schwarzschild criterion. The red line in the last plot shows
> the rough red-supergiant size limit.
>
> First of all, varying the parameter from 1.d-3 to 1.d-1 produces quite
> significant changes. But the crazier thing is that in all cases the CO core
> I get is uncomfortably small. For example, it would be really hard to
> explode 1.d-3 model, as the CO core is too tiny, even 1.d-1 case is still
> very degenerate.
>
> Please let me know if you find I made an error, also I would like to know
> how far people have tested this Langer's prescription in MESA?
>
> thanks,
> Tuguldur
>
>
>
>
>
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