COMMON ENVELOPE SIMULATIONS

Evolved binary runs planned/ongoing

Actively running now = bold

Run Run ID Progress Remaining cost Potential impact Energy conservation
EOS+CE (RGB) 248,252,253 runs but hangs medium high
RLOF+CE (RGB) 195 ran up to 47 d medium medium not yet checked
RLOF+CE (AGB) 264,265,266 runs but hangs high medium
CE equal mass particles (AGB) 263 ran up to 170 d low medium not yet checked
CE low mass companion (AGB) 259 ran up to 250 d none high 4% increase
CE (AGB), 4x higher resolution 267 ran up to 0.7 d high high not yet checked
Wind+accretion with low mass companion N/A not started low? medium Z.Chen+2017 setup

Runs

  1. Continued running Run 263 (equal particle mass AGB run). Now up to 170 days.
    • Next step is to plot separation and energy conservation, before resuming run
    • Goal is to explain the drag force at late times. Steps are
      1. test the Escala+2004 model using this run (263), and then
      2. try to generalize it to the unequal particle mass case, and compare with published AGB run (183)
  2. Started Run 267. Like published run (183) but max resolution is 4x higher.
    • It ran up to 0.7 days (3.0 frames) in 48 hours on 64 skx nodes; each chombo is 212 GB
    • Next step is to plot a(t), density slices, and energy conservation.
    • How does energy conservation compare to Run 183? If much better, then perhaps worth continuing.
    • Goal would be to run for 3 times as long as Run 183 (also serves as a convergence study).

Analytical model for WD 1856+534 system

  1. First key new idea is that planet 1 was actually a brown dwarf (maybe 50 M_J, i.e. about 0.05 Msun).
    1. Not massive enough to eject the envelope during inspiral
    2. But massive enough to expand the star, which engulfs planet 2 (this could happen at this stage or possibly later on)
    3. BD tidally disrupts and forms disk, which accretes and also spreads radially.
    4. Planet 2 inspirals and encounters disk.
    5. Accretion of disk material gradually releases potential energy, eventually resulting in envelope ejection.
  1. Second new idea is that planet 2 enters the disk left over from the tidal disruption of planet 1 and migrates, coming to rest near its present position. In this version of the model, there would be no need for planet 2 to eject any of the envelope (its ejection of <~1 % had always seemed like fine-tuning to me)
    • Is the disk spreading fast enough to spread out to the current separation of planet 2 (4 au) from disruption separation of planet 1 (~0.4 au)?
    • What governs the migration?
      • Is it type II migration (gap formation)?
      • Is the disk dense enough to pull the planet with it as it spreads viscously?
    • Does the planet still experience drag with the envelope while it is embedded within the disk?
      • Is the drag from dynamical friction or is it hydrodynamic, or are both important?
    • Assuming inward migration owing to drag balances outward migration owing to disc spreading, at what orbital separation does the planet come to rest?
      • Does it agree with the observed separation?
      • Or can we used the observed separation to constrain its mass?

Planetary winds

  1. Chatted with Eric about his analytic model
  2. Had the idea that turbulence in the wake behind planet might produce random motions with velocity ~v_orb~150 km/s
    • However, ambient stellar wind material is ionized so turbulence needs to be in neutral planet wind gas
    • Turbulence would be driven by K-H instability.
    • Using equation 2 of ​Hillier et al. 2020, I estimate that mixing leads to rms turbulent velocities of ~30 km/s, assuming a density contrast of 100 between planetary wind material and ambient stellar wind material. So unlikely to work.
  3. One difficulty with the magnetic field model is that the radial field is too small near the orbital plane if one assumes a dipole geometry.
    • However, it seems like beyond about 2 solar radii, the ​sun's field is almost radial (and curves into a Parker spiral further out) - see Fig. 1 of ​Owens+Forsyth 2013.
    • According to that last paper, the transition to radial occurs at the source surface, at a few solar radii. The planet is at 0.047 au ~= 10 Rsun, so a radial field is probably a reasonable (though somewhat optimistic) assumption.
    • See also this paper Eric sent which could be used to estimate the field strength in the stellar wind at the planet: ​Wang+Sheeley 2002.

Upcoming meetings

  1. CE meeting Tues July 20 to discuss runs
  2. WD planet meeting Tues July 27

Job interview

  • July 28 (requires quite a bit of prep)

Vacation

  1. July 30- back on Aug 9

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