[Mesa-users] Carbon Dredge-up/Third Dredge-up Efficiency and Timing in 1.3 Msun, Z=0.008 Model

[Frank Timmes]

the recent article https://academic.oup.com/mnras/article/527/4/9643/7491079 is also relevant.

fxt




> On Aug 25, 2024, at 9:03 AM, Frank Timmes <fxtimmes at gmail.com> wrote:
> 
> hi kayla,
> 
> take a look at mesa I, section 7.2.1, and especially figure 27.
> 
> then take a look at the c13_pocket test suite case, https://docs.mesastar.org/en/24.08.1/test_suite/c13_pocket.html#c13-pocket , which covers the third dredge-up for a ~0.9 msun structure. note the relative smallness of the spatial/temporal resolution controls that are needed to ensure the thermal pulse cycles and the c13 pocket are well resolved.
> 
> fxt
> 
> 
> 
> 
>> On Aug 25, 2024, at 12:23 AM, KAYLA MARTIN via Mesa-users <mesa-users at lists.mesastar.org> wrote:
>> 
>> Hi all,
>> 
>> I am having some issues with the efficiency of the third dredge-up to increase the C/O ratio in my star. I have specified the relevant model parameters currently in my inlist at the bottom of this email for reference.
>> 
>> The ultimate goal of my model is to become carbon rich (i.e., C/O > 1) by a total stellar mass of ~0.9 solar masses (after approx. 7-8 thermal pulses). The initial C/O ratio in the model is 0.23.
>> 
>> Currently, my model achieves C/O>1 only after ALL thermal pulses (approx. 9) have occurred, at a much lower total mass of ~0.6 solar masses. I believe this implies that the third dredge-up is ineffective until after the thermal pulse stage.
>> 
>> I am seeking suggestions on how I may trigger the third dredge up at an earlier time in my model, to achieve C/O>1 closer to a total mass of 0.9 solar masses. 
>> 
>> Thank you in advance! :)
>> 
>> 
>> Parameter settings for context... 
>> 
>> My model is a 1.3 solar mass star, with initial Z=0.008 (gs98 and gs98_co base compositions). The model has the following specified initial composition:
>>    • 
>> initial_h1 = 0.731924
>>    • initial_h2 = 0.000076
>>    • initial_he3 = 0.0000846
>>    • initial_he4 = 0.2599154
>>    • z_fraction_o = 0.53
>>    • z_fraction_c = 0.123
>> **The rest of the z_fractions are in other elements and are not so important to my goal.
>> My mixing parameters are set such that:
>>    • 
>> mixing_length_alpha=1.75
>>    • MLT_option='Cox' (as I want diffusive mixing)
>>    • use_Ledoux_criteron=.true.
>>    • alpha_semiconvection=0.04
>>    • thermohaline_coeff=2.0
>>    • overshoot_scheme(1)='exponential'
>>    • overshoot_zone_type(1), overshoot_zone_loc(1), and overshoot_bdy_loc(1)='any'
>>    • overshoot_f(1)=0.025 for pre-AGB phases and 0.008 for AGB onward
>>    • overshoot_f0(1)=0.005 for pre-AGB phases and 0.004 for AGB onward
>> 
>> I am currently using a Reimers wind scheme with scaling factor 0.477 on the RGB, and a Blocker wind scheme with scaling factor 0.01 (and have also tried 0.02) on the AGB.
>> 
>> _______________________________________________
>> mesa-users at lists.mesastar.org
>> https://lists.mesastar.org/mailman/listinfo/mesa-users
>> 
> 

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