[mesa-users] Odd mixing behavior in massive stars...

Josh Shiode jhshiode at berkeley.edu
Fri Aug 26 18:51:40 EDT 2011


Users,

It's been a while since I've contributed, but I've been here plugging away up here in Berkeley (including staying updated with MESA releases). 

So here's my question:

In evolving massive stars (I find issue with anything >~ 40 Msun), has anyone had problems with oddly behaving convection zones? The basic behavior I see is, usually during core hydrogen fusion, convection zones form near the original location of the convective core boundary and "roll" inward in mass until they connect with the core convection zone, dumping fresh hydrogen. 

For reference, I've started with the 40M_z1m4_to_si_burn test case inlist and modified to get what I've been working with. That case works swimmingly! As does m=40, z=0.02, opacity = electron-scattering (example is attached).

Depending on the parameters for mixing (Ledoux vs. Schwarzschild), semiconvection on or off, overshoot parameters, and so on and so on, this happens before or after (or both) hydrogen is exhausted in the convective core. You can see this in some of the attached Tioga "Internal Structure" plots from various runs of a 100 solar mass star with zero metallicity and electron scattering opacity (to address other issues in the atmosphere). This behavior seems to occur independent of overshoot being on (overshoot_f_* = 0.01) or off (overshoot_f_* = 0) and independent of global resolution over the range of 0.7 < mesh_delta_coeff < 2 and having (or not having) locally enhanced resolution using xtra_coeff_* = 0.1...

When fresh H is dumped into an exhausted core, the results are quite.. exciting, but I don't understand the origin of these shifting convection zones? I will continue exploring the mixing parameter space in search of less exciting evolutionary behavior in line with what I expect to see (smooth transitions from burning phase to burning phase), but I am hoping to get suggestions, feedback, shared experience,.. moral support(?) from the users on this. Anyone seen this before? Fixed it for themselves? 

The key to the pdfs is after "Internal_Structure_" the first letter is S/L for Sch or Ledoux criterion, O if there is overshoot, L/H for low or high res, and B if the resolution is enhanced at the boundaries. (I have more examples of these now, and will likely have even more in the next few days, if someone is interested.)

Thanks,


--
Josh Shiode
Graduate Student Researcher
NASA Earth & Space Sciences Fellow
Theoretical Astrophysics Center
University of California, Berkeley
753 Campbell Hall
jhshiode at berkeley.edu



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