Result

  1. High mass loss rate AGB star need a large atmosphere. Its photosphere will be around 1.5au. ​Liljegren et al. (2016) use 1.5au AGB and achieved . However, 1.5au will be too large for us. The tidal force will be 50% of the gravitational force from the AGB star. The highest mass loss rate I can do is . Below is the mass loss rate in 3-D simulation. I sum the mass flux through a 10 AU spherical shell. The luminosity of this AGB star is and mass is . So the mass loss rate and size is between RGB and super AGB.

  1. A detailed description of this AGB star model is:

AGB star model

There are two most important aspects in binary star simulation. One is the radiative transfer and the other is the AGB star model. The first one determine the large scale motion and morphology while the second one determine the robustness of inner boundary.

A sketch of the AGB star's structure is shown in the picture.

The hard pulsating sphere has velocity variation. Its amplitude is 5km/s and its period is 1 year.

The radius of the photosphere is also fixed. In reality, it must change but it is difficult to calculate. Within the photosphere, reduced gravity (80% of the original gravity) is being used. The reduced gravity has its physical stand - higher opacity inside the star but it is also because the resolution is poor. The simulation is resolving 2~3 order of magnitude density drop within 3 cells.

Between the photosphere and the dust formation zone, it is the gas opacity . The dust formation radii is calculated by

Where is first calculated by assuming that there is only gas in the simulation. When the is determined, I update the opacity where there is dust. The dust opacity is .

A questionable number is .

  1. A 3 AU separation simulation now will take about 5 days on 120 cores. I tested the resolution on single AGB star and it has a difference. The size of the simulation zone is . The previous resolution is base grid with 2 level of AMR. The current AMR is 3 while the base grid resolution is the same. The finest physical resolution is 0.05au thus the AGB star has 18 cells across its radii. The photosphere has 21 cells.
  1. I calculate the strength of tidal force by:

where is the binary separation. Substitute , , and you will get the value is close to 0.5 which is 50%.

  1. Currently I have some 3au and 4au simulations.
  1. 3au simulation:

I use or at the first 23 years. The AGB star is the same as in the single star case. After the simulation has come to a pattern state - the spiral shock escapes from the system. Below shows the pattern. Left figure shows the density plot and the right figure shows the temperature plot.

After 23 years, I make the AGB star dimmer by setting or . The spiral shock is not escaping in this situation but the simulation box is too small so we can not see its fall back.

The movie is here:

densitytop3au.gif​

  1. 4au simulation:

Interestingly, the 4au separation binary star will have non-escaping spiral shock when I put the normal AGB star () in the simulation. Also, the simulation box is too small.

The movie is here:

densitytop4au.gif​

It seems that 3au simulation has Roche lobe overflow while 4au simulation has wind Roche lobe overflow?

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Comments

1. Adam Frank -- 8 years ago

Hi Zhuo. This looks good in general.

Can you explain how your are calculating the effect of the tidal forces?

2. Adam Frank -- 8 years ago

Also can you tell us the resolution of the runs in terms of # of zones per AGB star radii.

What is the resolution of the new runs.

What is the resolution of the previous runs.

3. Zhuo Chen -- 8 years ago

Hi Adam,

Thanks for the comment.

I have updated point 3 and 4 to answer your questions.