6 au result

I found that the resolution of radiation field is very important.

I have run binary simulation with low radiation field resolution and high resolution. The low resolution one has Bondi-Hoyle accretion but the high resolution one has Wind Roche-lobe accretion. The difference comes from the radiation force on the gas. The lower resolution one has higher radiation force on gas thus drive a faster wind. The difference in radiation force is tiny and the terminal velocity should not be too much different (which I will go back and check the single 3D AGB star wind).

Below is the low resolution run. It is faster and more stable than the high resolution run. The image show the side view of the density, velocity and Mach number contour. The result is pretty much in line with previous research on BH accretion ​Shima et al. (1985)​Ruffert (1996). More specifically, it resemble the result of low gamma and high Mach BH accretion. This is very reasonable because the cooling in our model is in fact equivalent to decreasing the gamma.

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The temperature of outer region (near boundary) increases unphysically. This can be the inappropriate boundary condition in the co-rotating frame.

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Below is a snapshot of high resolution result. This run also has problem. But it shows that there is a bridge which resemble Roche-lobe accretion. However, the position of this bridge is not at the L1 point (not even close, probably 0.8~1.0 AU away). This may be a sign of wind Roche-lobe overflow.

Actually, when go from Roche-lobe to BH wind accretion. There should be a separation that the bridge appear and disappear as the AGB star pulsate. That state can distinguish the RLOF and BH accretion and be a sign of WROLF.

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