COMMON ENVELOPE SIMULATIONS

New Work

  1. New run (~half completed) with evolving softening length and resolution, larger box, and subgrid accretion turned off
  2. Enabled parallel HDF5 output and optimized code to get a bit of speed-up
  3. Started to analyze accretion onto the particles.

Results

  1. With accretion turned off, the accretion disk (torus) morphology is no longer present.
  2. It currently takes about 7000 node-hours on stampede2 skx nodes to complete 43 frames (10 days). But the speed actually varies because the radius of the refinement region as well as highest resolution are made to vary during the run. For comparison, our allocation for 2018 is for 166,000 node-hours. So if each run lasts for ~130 days, we are talking about no more than ~2 runs.
  3. The accretion rate increases montonically with radius of the control region, as might be expected. It approaches a state where Mdot oscillates around 0 for both the RG core and companion (the mass aroudn each particle stabilizes) BUT when the softening length is reduced, this seems to (artificially) cause more accretion to happen.

Run 143:

  • Similar to run 132 but with subgrid accretion turned off, twice larger box, resolution and softening length that evolve with time, less aggressive refinement, i.e. larger max refinement zones, and no relaxation (damping) run initially

Relaxation run: no relaxation run
First frame: 0
Last frame: 117 (so far)
Total simulation time: 27 sim-days
Machine and partition: Stampde 2 normal (completed up to frame 117, or 27 sim-days)
Number of nodes: 128 or 64, each with 68 (standard nodes) or 96 (skx nodes) cores
Total wall time: TBD
Hydro BCs: extrapolated
Poisson BCs: multipole expansion
Box size: L=8e13 cm (1150 Rsun)
Max refinement level: 4 (frames 0 to 72), then 5 (frames 72 to 117) Base resolution: 2.25 Rsun (2563 cells)
Highest resolution: 0.14 Rsun (40963 cells, 4 levels AMR, frames 0 to 72), and 0.07 Rsun (81923 cells, 5 levels AMR, frames 72 to 117)
AMR implementation: set by hand to have max level around RG core (frames 0 to 72) or companion (frames 72 to 117)
Max resolution zone: sphere around RG core, radius 5d12 cm (frames 0 to 46), radius 4d12 cm (frames 46 to 72), radius 3d12 (frames 72 to 103), radius 2d12 (frames 103 to 117)
Buffer zones: 16 cells
Softening length: 2.4 Rsun (frames 0 to 72), 1.2 Rsun (frames 72 to 117)
Ambient density: 6.7e-9 g/cc
Ambient pressure: 105 dyne/cm2
DefaultAccretionRoutine=0 (no accretion)

Movies of run 143
1) Edge-on slice, centered at companion. Left: slice through both particles. Right: slice through P2 as viewed from direction of P1.
​edge-on
2) Face-on slice, centered at companion.
​face-on slice
3) Zoom-in face-on slice, inertial frame.
​face-on slice
4) Full box face-on slice, inertial frame.
​face-on slice, full box

Snapshots of run 143
Left: edge-on, slice through both particles (view centered on companion with side of 4e12 cm). Right: same but zoomed in by 4x.
http://www.pas.rochester.edu/~lchamandy/Graphics/RGB/Post-sink_particle/Post-modified_Lane_Emden/Damp143/rho2D_P2_2e12_edgeon_throughP1_andP2_0100.png http://www.pas.rochester.edu/~lchamandy/Graphics/RGB/Post-sink_particle/Post-modified_Lane_Emden/Damp143/rho2D_P2_5e11_edgeon_throughP1_andP2_0100.png

Inter-particle separation
Red horizontal lines show radius of maxLevel refinement region. Green horizontal line shows softening length (solid) or five times softening length (dashed) for each particle. Finest resolution is proportional to softening length, i.e. resolution improves by factor of 2 when softening length is reduced by factor of 2. Vertical lines show transition from one refinement radius to the next (dotted red, 5e12 to 4e12 to 3e12 to 2.5e12 cm), and transition from one softening radius to the next (green dashed, ~2.4 Rsun to ~1.2 Rsun)
http://www.pas.rochester.edu/~lchamandy/Graphics/RGB/Post-sink_particle/Post-modified_Lane_Emden/Damp143/p_143_extended.png

Mass accretion
Accreted mass with time (blue) and accretion rate with time (red) inside spheres around RG core (top) and companion (bottom) of different control radii. Plot of orbital separation is also shown for comparison. The bottom two plots are the same as the upper two plots except that data from an additional control radius is added, and individual points are not overplotted on the curve.
http://www.pas.rochester.edu/~lchamandy/Graphics/RGB/Post-sink_particle/Post-modified_Lane_Emden/Damp143/macc1_143_largeradius.png
http://www.pas.rochester.edu/~lchamandy/Graphics/RGB/Post-sink_particle/Post-modified_Lane_Emden/Damp143/macc2_143_largeradius.png
AAhttp://www.pas.rochester.edu/~lchamandy/Graphics/RGB/Post-sink_particle/Post-modified_Lane_Emden/Damp143/p_143_simple_extended.png
http://www.pas.rochester.edu/~lchamandy/Graphics/RGB/Post-sink_particle/Post-modified_Lane_Emden/Damp143/macc1_143_largeradius_3radii.png
http://www.pas.rochester.edu/~lchamandy/Graphics/RGB/Post-sink_particle/Post-modified_Lane_Emden/Damp143/macc2_143_largeradius_3radii.png

Comments

  • Accretion onto companion takes place within ~10 days and then the mass becomes fairly steady.
  • Which control radius is most appropriate? The total mass accreted seems to be of order 0.01 Msun or 1% of the companion mass.
  • There is an anticorrelation between the mass inside the sphere and the particle separation, which makes sense.
  • There is a sudden increase in the accreted mass when the softening length is reduced by a factor of 2, especially for the RG core. This makes sense because the particle's gravity becomes stronger inside of the original softening radius. It's not clear how much of a role this is playing, and it will be interesting to see what happens when we halve the softening length again later in the run.
  • Accretion rates onto the companion are of order 0.1 to 1 Msun/yr, which is super Edington, though not as high as what we were getting with Krumholz accretion turned on.

Next steps

  • Complete the simulation up to at least 300 frames (about 70 days), using stampede2 skx nodes
  • Analysis of:
    • mass accretion with time
    • angular momentum accretion with time
  • Clean up presentation of movies/snapshots
    • reference frames/views
    • velocity vectors in particle frame
    • units
    • labels

To think about

  • Had we been able to use an arbitrarily small softening radius from t=0, would the steady-state accreted mass be higher? If yes, then would the amount of gas left over in the envelope have been significantly affected? Would the orbit of the particles have been significantly affected?
  • As a reminder, the strategy is to keep the number of resolution cells per softening length constant (~17), and to keep the number of softening lengths spanning the separation between the two particles at >5 (as done by Ohlmann 2016).

Comments

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