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

[KAYLA MARTIN]

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.*
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