[mesa-users] Fwd: semiconvection (typo)

[Tuguldur Sukhbold]

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
> 
> 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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