COMMON ENVELOPE SIMULATIONS

EoS stuff

Work done

  1. More plots and analysis of MESA RGB
  2. Downloaded and installed latest version of MESA (12778 instead of 8845). Ran "same" MESA simulation with this version and compared to old sim.

Results

  1. Initial conditions
    1. ​RGB energy profiles.
    2. ​mass fractions (direct MESA output).
    3. ​number densities of ions, neutrals and electrons. Oxygen shown as an example but can also plot C, N, Ne, Mg.
    4. ​neutral fractions (direct MESA output).
    5. ​mean atomic weight.

Discussion

  • Gas thermal energy + recombination energy (+Prad which is negligible) almost equals to internal energy but a small decrement that grows with radius, becoming sizable right near surface.
  • Went to trouble of including metals but rather negligible!
  • Used Saha equation with T—>0 partition functions, which are just the degeneracies of states (so positive integers). In reality the partition functions can be much larger at the temperatures found in the star >~104 K. And their ratios, which is what is important for the Saha equation, can change appreciably. One can estimate these from atomic databases (NIST, ViZieR) but numbers can also depend on electron pressure…complicated. What effect would this have on the recombination energy?
  • Found that the average atomic mass of metals is 17.35. This is an input into Yisheng's code that produces the tabuler EoS because it is a parameter for the ideal EoS part of the table. He used 18 and anyway, the ideal EoS part of the table is rarely utilized.
  • Found that new MESA version 12778 gives very similar results. Should we go with new MESA RGB model or stick with the old one?

Next steps

Initial conditions

  • Estimate recombination energy using partition functions from NIST and/or ViZier databases and see what difference this makes.
  • Learn more about the EoS to understand what other physics contributes near the surface (optically thin region).
  • Put all the MESA profile figures in a pdf, with figure captions, for reference (to be used throughout the EoS CE project).
  • Write a short section on EoS for the paper while it's all fresh, with help from Yisheng and Jonathan.

Simulation

  • Reproduce tables using mean atomic weight of metals as 17.35 instead of 18 (differences will be minor but might as well).
  • Steps mentioned in last blog post.

Idea for paper

  • I had the idea of subtracting out the recombination energy (physically it is escaping by radiating away) and seeing what effect this has. Results will be at least somewhat different from ideal gamma=5/3 EoS. But it would also be interesting to do a run where we subtract ONLY the H recombination energy, say, to see what happens if recombination energy of hydrogen leaks out, but that of helium (and metals) is retained, to constrain the importance of H rec energy vs He rec energy.

Comments

No comments.