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

[Jakub Ostrowski]

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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