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

[Frank Timmes]

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
>