[mesa-users] off-center Ne and O burning (again…)

Bill Paxton paxton at kitp.ucsb.edu
Sun Apr 21 16:00:03 EDT 2013 

Hi Stan,

good advice.   I went part way by reducing that parameter, but your
suggestion is to turn it off completely -- which can be done by setting

	prune_bad_cz_min_Hp_height = 0

along the same lines, it would be worth changing the following controls to .false.

	 remove_mixing_glitches = .true. ! if true, then okay to remove gaps and singletons
	 okay_to_remove_mixing_singleton = .true.

Let's try it.   Tug, Jakob, Josh, and others: please give this a try and let us know.
I'll run the mesa test suite with these changes and see what happens there.

Bill





On Apr 21, 2013, at 12:43 PM, Stan Woosley wrote:

> Just a thought. When semi convection is small or turned off in a code
> the response is often to create many small alternating convection zones,
> often only a few zones thick. These come and go out of phase and 
> act as a staircase that can mimic the effects of semiconvective mixing. I think
> Icko Iben first saw this many years ago.
> 
> Anyway, it may not be  a good scheme to ignore convection anywhere
> that the gradients say it should occur, even if its just a few zones.
> 
>   Stan
> 
> 
> 
> On Apr 21, 2013, at 12:52 AM, Jakub Ostrowski <ostrowski at astro.uni.wroc.pl> wrote:
> 
>> Hi!
>> 
>> I'm working almost exclusively on 15 M_s models and I have found quite a big difference between the v4906 and previous ones too - but somewhere else than you.
>> 
>> I studied properties of models after depletion of central H, logTeff ~ 4.30, logL ~ 4.63. The behavior of Brunt-Vaisala frequency is much smoother in v4906 than before and finally now there is convection where it should be according to behavior of gradients.
>> 
>> And this is due to one change in controls.default. Now there is
>> 
>> prune_bad_cz_min_Hp_height = 0.1 ! lower limit on radial extent of cz
>> 
>> whereas previously the value was 1.0. I don't know if this is useful for you but for me this previously overlooked parameter made a huge change in case of my model. But it seems there is no dramatic influence on the shape of  track on HRD.
>> 
>> Take care,
>> Jakub
>> 
>> On 21 kwi 2013, at 06:59, Tuguldur Sukhbold <sukhbold at ucolick.org> wrote:
>> 
>>> Dear MESA users,
>>> 
>>> I am getting 2 different results with the exact same inlist for two different versions of the code: 4798 and the current 4906. Since MESA is constantly being developed, I understand that we should expect changes between the versions. However I am little surprised to see such a 'big' change in two releases came out almost one after the other.
>>> 
>>> The attached plot shows the central T-Rho plane evolution for 15Msun model with the following simple inlist:
>>> 
>>> &star_job
>>> 
>>>     mesa_dir = '' 
>>>     create_pre_main_sequence_model = .true.
>>> 
>>>     set_rate_c12ag = 'Buchmann'
>>>     num_special_rate_factors = 1
>>>     reaction_for_special_factor(:) = 'r_c12_ag_o16'
>>>     special_rate_factor(1) = 1.2
>>> 
>>>     eos_file_prefix = 'mesa'
>>>     kappa_file_prefix = 'gs98'
>>> 
>>> / !end of star_job
>>> 
>>> &controls
>>> 
>>>     initial_mass = 15
>>>     initial_Z = 0.02
>>>     initial_Y = 0.25
>>> 
>>>     mixing_length_alpha = 2
>>> 
>>>     RGB_wind_scheme = 'Nieuwenhuijzen'
>>>     AGB_wind_scheme = '' 
>>>     RGB_to_AGB_wind_switch = 1d-4
>>>     Nieuwenhuijzen_wind_eta = 1.0d0
>>> 
>>>     photostep = 50
>>>     profile_interval = 25
>>>     history_interval = 1
>>>     terminal_interval = 10
>>>     write_header_frequency = 10
>>> 
>>> !hign
>>> !      xa_central_lower_limit_species(1) = 'h1'
>>> !      xa_central_lower_limit(1) = 0.72
>>> !hdep
>>> !      xa_central_lower_limit_species(1) = 'h1'
>>> !      xa_central_lower_limit(1) = 0.01
>>> !heign
>>> !      xa_central_upper_limit_species(1) = 'c12'
>>> !      xa_central_upper_limit(1) = 0.01
>>> !hedep
>>> !      xa_central_lower_limit_species(1) = 'he4'
>>> !      xa_central_lower_limit(1) = 0.01
>>> !cign
>>> !      log_center_temp_limit = 8.69897 !0.5d8K
>>> !cdep
>>>     log_center_temp_limit = 9.07918 !1.2d9K
>>> !odep
>>> !      xa_central_lower_limit_species(1) = 'o16'
>>> !      xa_central_lower_limit(1) = 0.05
>>> 
>>> /
>>> 
>>> If you guys remember, I have previously brought up the issue of off-center O burning, in the case of alpha_mlt = 1, in version 4798. This behavior was gone if I set this parameter to alpha_mlt = 2, as it creates a larger CO core. However, when I try to recreate the older results with the current version of MESA - 4906 - I am facing the off-center burning issue again with alpha_mlt = 2. 
>>> 
>>> In the response to my previous email, Bill has reported that he got the same result (no off-center burning) with alpha_mlt=2 in his version of MESA - 4917.
>>> 
>>> MESA version	alpha_mlt=1	alpha_mlt=2
>>> 4798			y			n
>>> 4906			y			y
>>> 4917			y			n
>>> 
>>> (yes/no to off-center Ne and O burning)
>>> 
>>> I haven't seen anything in the release email from Bill for 4906, that might be relevant to what I see here. 
>>> 
>>> In general, 15Msun is a funny mass in MESA. It is sitting on the border of two different paths of evolutions of CO core: (1) degeneracy is important and off-center burnings of Ne and O as we've seen (2) degeneracy effects are no longer important and everything ignites in the center first. In other words, 15Msun model essentially with all the default settings, is producing a CO core mass that borderlines these two paths. This is why changing parameters here and there are producing these rather big changes for this 15Msun case. I don't think one will see this behavior in bigger mass models in any version of the code with any alpha_mlt, simply because the CO core will be big enough.
>>> 
>>> From my experience, this funny mass is usually much lower in other codes, more like in the 8-12Msun range.
>>> 
>>> Tuguldur
>>> 
>>> 
>>> 
>>> <inc.png>
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