Posts for the month of September 2021

COMMON ENVELOPE SIMULATIONS

Jet paper

  • https://www.overleaf.com/project/601963d151b22065e09417a9
  • Meeting?
  • Figures still need improvement (see my comments in the figure captions)
  • A bit more analysis
    • J8 (WD run)
    • J2 (half companion mass run)
    • normalized binding energy slices (blue-red) to get a sense of where extra unbinding is happening

EOS project

  • Run 271 has now reached Frame 83 (almost 20 days)

https://www.pas.rochester.edu/~lchamandy/EoS/Figures/p_mult_271_143.png
https://www.pas.rochester.edu/~lchamandy/EoS/Figures/Mass_143_271.png
https://www.pas.rochester.edu/~lchamandy/EoS/Figures/Energy_percent_change_new_271.png

APN8e Talk

  • Given the time constraint (12 minutes + 3 minutes for questions) I have decided to talk only about the jet paper

COMMON ENVELOPE SIMULATIONS

New EOS runs

  • Similar to fiducial RGB run from Papers 1-4.
    • Same r_soft=2.4 Rsun
    • Same ambient density and pressure
    • 1 extra level of AMR around particles to improve energy conservation
    • A bit more automation to refinement part of code
    • Uses more recent version of AstroBEAR
    • If energy is well conserved can evolve up until separation = 2 r_soft=4.8 Rsun (do not expect full unbinding by then)
  • This is less ambitious compared to first two attempts which used factor of 6.7 lower density ambient, 4x smaller softening length, and either 3 or 2 extra levels of AMR around particles compared to fiducial run from Papers 1-4 (but these runs kept hanging, apparently due to insufficient memory).
Description Run ID Paper Primary Secondary Status Last complete frame Remaining cost Hanging? Resolution Ambient density Comments
MESA EOS 271 EOS RGB 1 Msun In progress 23 ~25% of remaining SUs? Not so far 4 AMR (envelope), 5 AMR (near particles) 6.7e-9 g/cc As fiducial RGB Run 143 but with extra AMR level, tracers for core/envelope/ambient and for initial ionization, and some minor code improvements including a bit more automation
MESA EOS without recombination energy ? EOS RGB 1 Msun Not yet submitted -1 ~25% of remaining SUs? N/A 4 AMR (envelope), 5 AMR (near particles) 6.7e-9 g/cc Same as Run 271
MESA EOS without hydrogen recombination energy (but including helium recombination energy) ? EOS RGB 1 Msun Not yet submitted -1 ~25% of remaining SUs? N/A 4 AMR (envelope), 5 AMR (near particles) 6.7e-9 g/cc Same as Run 271
Ideal gas EOS (gamma=5/3) ? EOS RGB 1 Msun Not yet submitted -1 ~25% of remaining SUs? N/A 4 AMR (envelope), 5 AMR (near particles) 6.7e-9 g/cc Same as Run 271

CE

Allocation usage

  • Already used almost 2/3 of present allocation (expires 6/30/2022)
  • Of that which was used, 2/3 was used for jet runs and 1/3 was used for other runs

Projects and Simulations

Paper Runs Run IDs Progress Last complete frame Remaining cost Hanging? Resolution Ambient density Comments
CE jet See paper on Overleaf 10 runs (9 main sequence + 1 white dwarf companion) Completed 173 0 No 4 AMR 6.7e-9 g/cc Run by Amy
EOS AGB: As C+20 but with (1)MESA EOS; (2)MESA EOS without recombination energy; (3)MESA EOS without hydrogen recombination energy (but including helium recombination energy) 270/ ? / ? In progress/ Not yet started/ Not yet started 72 / -1 / -1 ~80% of remaining SUs Sometimes, but after running for ~36 hours 3 AMR (envelope), 5 AMR (near particles) 1e-9 g/cc I'm also retrying the original RGB EOS run which has higher resolution (4 AMR for envelope, but now 7 AMR near particles), smaller softening length (0.6 Rsun instead of 2.4 Rsun), lower ambient (1e-9 g/cc instead of 6.7e-9 g/cc), tracers for core/envelope/ambient and for initial ionization, and some minor code improvements including a bit more automation
WD planets paper II RGB or AGB +low mass companion 151(RGB+0.25 Msun companion)/ 259(AGB+0.01 Msun companion)/ 268(AGB+0.08 Msun companion, ideal gas EOS)/ 269(AGB+0.08 Msun companion, MESA EOS) Completed / Completed / Paused / In progress 173 / 1366 / 264 / 271 ~20% of remaining SUs — will keep running 269 but 268 was hanging so I will keep it on pause for now Sometimes 4 AMR for RGB run 151 / 3 AMR (envelope), 5 AMR (near particles) for AGB runs 6.7e-9 g/cc for RGB run / 1e-9 g/cc for AGB runs To get a sense of how much expansion is possible during plunge-in for a low-mass companion. See also recent work by Kramer+2020
Drag force paper II AGB: As C+20 but now companion has same mass as primary core particle (0.53 Msun, instead of 1 Msun) 263 Completed 1291 0 Happened 1 time 3 AMR (envelope), 5 AMR (near particles) 1e-9 g/cc With particles of equal mass, we can use/test the phenomenological model of Escala+2004 which was applied to inspiraling super-massive black holes of equal mass, because with equal particle masses there will be extra symmetry at late times, which simplifies the problem and could therefore lend itself better to physical interpretation…remember our goal is to understand and model the drag force at late times, something we left for future work in C+19b
Neutron star CE Jet Similar to 10xEddington jet run, but with ~1.6 times higher Mdot and ~35 times higher jet speed ? Cannot make it to frame 1 (times out on stampede at frame 0.7 or 0.8) 0 ~estimated 35 times as expensive as typical jet run and ~3.5 times as expensive as WD jet run Not so far 4 AMR 6.7e-9 g/cc Set up and attempted by Amy. Runs but just takes long (lots of resources). Would be high impact research. Would likely not be quenched. Nothing comparable in the literature.

Questions

  • Use of Frontera?
  • NS jet run
    • Jet speed 0.1c — could it be smaller — or should it be larger (simulation time is roughly proportional to jet speed)?
    • Shorten frame time? But even then we lack SUs on Stampede
    • Is present fixed Mdot_Jet with Krumholz accretion good enough — or should we cap accretion rate at 10Mdot_jet? — or should we set Mdot_jet to equal 0.1 Mdot_acc?

Numerical Methods

I have extended my Riemann solver for use in a Godunov reconstructions. I then ran the results using Riemann-problem like setups (see table 6.2 and figures 6.8-6.12 of Riemann Solvers and Numerical Methods for Fluid Dynamics by Toro) and compared the Godunov solution (blue) to the exact Riemann solution (green). Plots are (top to bottom) density, velocity, pressure.

One caveat worth mentioning is that I didn't implement a method to compute timesteps and instead just use a sufficiently small fixed tilmestep. Not the most efficient way to do it but it allows me to verify that I understand the concept behind a Godunov solver, and it still ran fast enough where I couldn't tell

Since then I have implemented various approximate solvers. Examples include Two-Rarefaction Riemann Solver (TRRS), Primitive Variable Riemann Solver (PVRS), and the Roe solver. Pictured below is the same Godunov method using the Roe solver:

Approximate solvers allow us to bypass the iterative nature of the exact Riemann solver, which allows for a considerable speedup when simulating more complex problems. Most approximate solvers however suffer one or more shortcomings. For example, the roe solver tends to do well with discontinuities, but often fails with rarefactions as a result of entropy violation. One option for handling this is to use an adaptive solver, which selects a solver based the type of solution expected.

Whether exact or approximate solvers are used, the Godunov method used so far is accurate only to first order. Improvements can be achieved using various techniques, such as the Weighted Average Flux (WAF) and Total Variation Diminishing (TVD) schemes. Compared to the first order methods, discontinuities and rarefactions are much sharper when using higher order accuracy, at the expense of an increased chance of various numerical artifacts.

Below I have implemented a WAF-TVD scheme using an exact solver. A notable challenge with this scheme in particular (which gave me some trouble) is that for most solvers (including the exact solver) an extra step is required to handle rarefactions.

Lastly I have been reading about splitting schemes, which allow for solutions to equations with source terms. I have not yet implemented these, but these will be particularly important for me to understand since my research focuses on the effects of a source term (technically it's a sink term) in the energy equation.

COMMON ENVELOPE SIMULATIONS

Insights from CEPO2021 conference

  • Noteworthy viewpoints?
    • Convection is too slow to be important (Fritz Roepke)
    • Triples are extremely important (Silvia Toonen)
    • The collimation mechanism for PNe does not work (Noam Soker)
    • The mechanism we proposed for explaining WD planets does not work (Noam Soker)
    • Accretion rates and jet feedback efficiencies are too low to matter (Hagai Perets)
  • Opportunities?
    • Accretion and jets — super-Eddington, hyper-Eddington, neutron stars
    • Triples
    • Eccentricity
    • Mergers
    • "Double CE"
    • GW waves, especially during mergers
    • Zoom sims to study accretion (long way off but we have good tools)
    • MHD (do we get the jets seen by the AREPO group?)

Papers in progress

  • Jet paper (will be ready soon, plan to submit by Month's end)
  • WD planets paper II (plan to submit by year's end)
  • EOS paper
    • Recall that I moved from RGB to AGB since could not get RGB to work at "modern" resolution and ambient density (code HANGS)
    • AGB run is going on "okay" but also sometimes HANGS — this is the test run
    • I must redo the EOS analysis of MESA profile using the AGB star (not that hard)
    • Plan to make the improvements to the code that were there in the old EOS RGB run that was hanging
      • automatic refinement shape modification (depending on inter-particle separation)
      • tracers
        • ambient/star/core region
        • HI/HII/HeII/HeIII
    • Then plan to perform 4 runs
      • MESA EoS without radiation — must verify that radiation is unimportant for AGB star
      • MESA EoS without recombination energy or radiation
      • MESA EoS without hydrogen recombination energy or radiation
      • Ideal gas gamma=5/3 (or use old run if we have to)
  • Force paper II (future)
    • understanding the drag force at late times
    • equal particle mass simulation (Run 263, now completed) and Escala+04 model…

Simulation work

Completed

  • Run 259: AGB run with 10 M_Jupiter companion (ran up to frame 1366 and completed analysis — may use it for WD planets paper)
  • Run 263: AGB run with 0.53 Msun companion, equal to mass of core particle (ran up to frame 1291 and completed analysis — for future force paper)

Paused

  • Run 268: AGB ideal gas run with 0.08 Msun companion (reached frame 265 and hangs; I have paused it for now — for use in WD planets paper)

In progress

  • Run 269: AGB MESA EOS run with 0.08 Msun companion (reached 245 and I'm still running it, but about half as fast as 268 — for use in WD planets paper)
  • Run 270: AGB MESA EOS run (reached frame 36 out of ~1137, hangs but maybe problem is just a one-off)

Initial Runs with unequal flows and realistic cooling

The first run here is a reference case with equal flows and a realistic cooling curve.

For the next six runs, the top jet remains unchanged, with only the bottom jet being changed. First, we lower the density of the bottom jet while keeping the radius fixed.

Next, we have two runs where the radius is varied and the density is varied proportional to the inverse square of the radius; this keeps the mass of any 'gaussian pillbox' fixed (provided the pillbox contains the entire radius of the jet.

Here the radius is again varied, but this time density remains unaltered from the reference case. We see that a change in the radius of the jet does not cause the interaction region to move after collision, but does have a noticeable impact on the spray.

Finally, we change the jet velocities from 70 and 70 km/s to 80 and 60. In the first of these two runs density remains unaltered from the reference case, while in the second run density is increased to keep the mass flux fixed. Note that the top jet still has a higher ram pressure and thus the interaction region still moves.

Next step is to rerun a few of these at a larger scale. Some of the runs are being run in a 128x128x128 box (original is 64) at lower refinement to better study the spray, while another set of runs (not mutually exclusive) are being rerun in 32x32x16 at higher refinement to better resolve the interaction region. I began by rerunning the reference run in both cases, while I work on selecting 2-3 additional runs for each type.

Even with the restricted region, the higher level of refinement results in the interaction region run only about 10-15 frames per day. Currently it is on frame 117, shown below:

Meanwhile rerunning to focus on the spray produced nearly 900 frames within a period of about a week