Posts for the month of March 2022

CE

Research Plans and Ideas

Papers based on existing simulations

Paper Idea Description Simulations Status Comments
Drag Force II Model drag force at late times Runs 183, 263, 277, 282 Sims completed Sim 263 is like published AGB Run 183 but with particles of equal mass, to simplify modeling (​Escala+2004)
Time-dependent energy formalism Extend/generalize energy formalism using insight from simulations Run 183, perhaps others as well Stalled because initial evolution is hard to reconcile with the new formalism Should be possible to get around this or just exclude early times
CE planet II Extend C+21 model Runs 259 (AGB+10MJup planet), 268 (AGB+0.08Msun, ideal gas), 269 (AGB+0.08Msun, MESA EOS) Notes and presentations but no write-up yet Simulations were not really successful, but Run 259 is first of its kind so worth presenting for its intrigue

Ideas for new simulations

Simulation Type Description Development needed Comments
Neutron star jet New regimes/ Parameter space exploration companion is a NS launching a powerful jet Ideally would improve accretion/jet model (AstroBEAR already allows for this). High velocity jet makes run expensive. Ideally would do one run with existing RGB primary and one with a massive primary.
Envelope ejection? Improve numerics Extend a simulation all the way to envelope ejection Reduce ambient, expand box, increase resolution Need to try running with a lower ambient energy density and compare to existing runs to see what we can get away with, need to look at energy conservation more carefully. Requires lots of computer time which we do not currently have.
Vary initial separation Parameter space exploration/ New regimes Compare sims with different initial separations, try to obtain RLOF phase Unclear, perhaps not much Expensive because of longer periods. Preliminary sims were done long ago: suggests that higher a_i leads to higher eccentricity during plunge-in. Existing work: ​Reichardt, De Marco, Iaconi, Tout & Price 2019
BD/planet companions New regimes Improve efforts to simulate RGB/AGB with BD/planet companion Not much, perhaps Expensive because of long orbital time. Only (modern) existing work: ​Kramer, Schneider, Ohlmann+ 2020
Include MHD New physics Include MHD in our best fiducial RGB run and see what happens Setup should not be too complicated, but bugs are likely Makes sense considering that our group has expertise in MHD. Only existing work: ​Ohlmann+2016b, ​Ondratschek, Roepke, Schneider+ 2021(preprint)
Include radiative transfer New physics Include flux-limited diffusion (already implemented into AstroBEAR) Needs lots of testing and learning the theory, need to put in MESA opacity tables and figure out how to use them Only existing work is a conference proceedings: ​Ricker+2019, the effect for our fiducial model is likely to be rather negligible. Realistic convection likely requires radiative transfer?
High mass regime (NS-NS merger progenitors) New regimes CE involving 8Msun primary and NS secondary Will likely require higher resolution. Larger range of scales so probably more challenging. May be expensive. One existing self-consistent global sim: ​Moreno+2022(preprint)
CEE involving two giant stars New regimes Binary pair is evolving to RGB at almost same time so get a CE involving envelopes of both stars Should not require much Would be expensive. No existing simulation? But see: ​Schneider+2019
Triple systems New regimes Introduce a second companion (multiple orbital configurations are possible) Not much, probably Triples may be quite important (according to S. Toonen). Limited number of existing simulations: ​Glanz+Perets 2021

CE

New Analysis

2D plots showing Spatial and Temporal dependence

​Helium
​Hydrogen
Conclusions:

  • Helium seems more important than hydrogen.
  • Recombination at first but then stagnates. Heating from inspiral balances cooling by expansion?

Ionization and Recombination (Volume-integrated, showing evolution with time)

​Results
Conclusions:

  • Helium recombination HeIII —> HeII and HeII —> HeI are the dominant transitions
  • However, after t = 25 days, there is no net release of recombination energy

Energy terms (Star gas only, excludes ambient), evolution with time

All energy terms, not accounting for fluxes out of box: https://www.pas.rochester.edu/~lchamandy/EoS/Figures/Env_E_terms_with_init_th_277_282_spancols_individ_totals.png
Zoom-in on change in the recombination energy: https://www.pas.rochester.edu/~lchamandy/EoS/Figures/Env_E_terms_with_init_th_277_282_spancols_individ_totals_zoom.png
Conclusions:
1st Figure:

  • In both tabular EOS and gamma=5/3 runs, particle energy decreases at a steady (and still substantial) rate after t ~= 57 days, implying that the inpsiral does NOT stall.
  • Differences between runs are very small (<10%) implying that ionization and recombination do not play a very important role up until this point in the evolution
  • The release of recombination energy between about t = 6 days and t = 25 days leads to a slightly higher thermal energy compared to gamma=5/3 run (the two energy changes roughly balance one another, which makes sense).
  • EOS case manages to reduce gas-particle PE terms (by puffing up envelope?) after t ~= 45 days. From t ~= 45 days to t ~= 80 days, we also see a reduction in the thermal energy in the tabular EOS run as compared to the gamma=5/3 run, which is consistent with a puffing up. But this effect has faded by the end of the simulation at t ~= 80 days. This coincides with a transition from a deeper inspiral (compared to gamma=5/3 run) to a shallower inspiral (see also separation results, below).

2nd Figure:

  • The peak amount of recombination energy released is about 10%, which happens at t ~= 24 days
  • Thereafter, the net recombination energy relased reduces and drops to only 1% by the end of the simulation at t ~= 80 days.
  • The evolution of the recombination energy agrees well with the expectation from the ionization/recombination analysis above (using tracers and the Saha equation) FOR THE FIRST 20 DAYS. After that the tracer/Saha analysis predicts that almost 0 recombination energy is released whereas the plot of recombination energy (i.e. internal minus thermal) says that the net release of recombination energy between t ~= 20 days and t ~= 80 days is negative.
  • It is important to understand the reasons for this discrepancy

Inter-particle Separation, evolution with time

Separation curve: https://www.pas.rochester.edu/~lchamandy/EoS/Figures/p_mult_282_283_277.png
Conclusions:

  • Mean separation continues to decrease at the ends of both simulations (though at an ever-decreasing rate of decrease)
  • There is very little difference between the runs. Suprisingly, the difference between the MESA EOS run (with radiation energy removed — blue curve) and the tabular EOS run with internal energy replaced by thermal energy (green curve) is larger than the difference between MESA EOS and gamma=5/3 (red) curves.
  • Comparing MESA EOS (blue) and gamma=5/3 (red) curves, the MESA EOS run shows slightly smaller separation between t ~= 25 days and t ~= 70 days and slighly larger separation thereafter

Envelope Unbinding (Volume-integrated), evolution with time (showing Star tracer mass only)

With factors of two in particle-gas potential energy terms: https://www.pas.rochester.edu/~lchamandy/EoS/Figures/EnvMass_282_283_277.png
Without factors of two in particle-gas potential energy terms: https://www.pas.rochester.edu/~lchamandy/EoS/Figures/EnvMass_282_283_277_half.png
Conclusions:

  • Using the "internal energy" criteria (which makes no sense) would imply that the unbound mass is much higher, as found by other authors (top curve in both plots, and other authors use the equivalent of the second plot)
  • Using another criteria for unbound which is more reasonable, the MESA EOS run does lead to a higher unbound mass, of order 10% larger, peaking somewhere between t ~= 25 and t~= 40 days.
  • By the end of the MESA EOS simuation at t ~= 80 days, the difference is basically 0
  • The MESA EOS simulation with internal energy replaced with thermal energy (green/yellow) is much more similar to the gamma=5/3 run, as would be expected. But this run generally falls between the other two. This suggests that the recombination energy is actually slighly less important than the difference between blue and red curves would suggest.
  • Note that after t ~= 50 days, significant mass from the original primary is leaving the box, about the same in both runs (about 5% by t=85 days).
  • Generally speaking, the unbound mass is growing steadily by the end of both simulations (irrespective of what criterion for unbound is used)

Energy conservation, evolution with time

Results: https://www.pas.rochester.edu/~lchamandy/EoS/Figures/Energy_percent_change_new_282_283_277.png
Conclusions:

  • Energy is conserved to within ~2%, where the denominator chosen for this calculation is indicated on the plot
  • If one ignores the energy loss from reducing the softening radius, it is more like ~4% for the gamma=5/3 run and <1% for the MESA EOS run
  • The energy conservation inside the sphere with radius Lbox/2 (centered on the origin) is probably better: the gravitational potential due to mass outside this sphere is NOT included in the code, so envelope mass leaving this sphere reduces the gravitational PE inside the sphere, leading to an energy increase. This is likely the cause of the increase seen at the end of the simulations.

Status of runs

  • Run 277: MESA EOS (analyzed up to frame 344 or 77 days, completed up to frame 377 or 87 days)
  • Run 282: Ideal gas gamma=5/3 EOS (analyzed up to frame 374 or 87 days, completed up to frame 407 or 94 days)
  • Run 283: MESA EOS with recombination energy removed from EOS tables (completed up to frame 218 or 50 days on Frontera)
  • Run 276: MESA EOS with maxlevel increased by 1 compared to Run 277 (for convergence study — completed up to frame 47 or 11 days on Frontera)
  • Run 28?: MESA EOS with maxlevel reduced by 1 compared to Run 277 (for convergence study — not yet started on Frontera)
  • Run 271: MESA EOS with 7 times higher ambient (to explore role of ambient) (completed up to frame 235 or 54 days and will not extend)
  • Run 143 (fiducial run of past papers): Ideal gas gamma=5/3 EOS with 7 times higher ambient (to explore role of ambient) (completed up to frame 173 or 40 days and will not extend)

Next steps

  • Energy terms — include flux in total energy of primary gas tracer
  • Anvil
  • Continue to extend Runs 277 and 282 — but for how long?
  • Extend Run 276 (high res run)
  • Make progress on paper write-up
  • Explore overlapping ionization species regions to get a sense of how important they might be (< 10% difference?)
  • Calculate total angular momentum and check angular momentum conservation
  • PostProcessing to check energy conservation within sphere of radius Lbox/2 — expect it to be better than that in full box