Meeting Update 1008

Star formation: I've been doing more triggered star formation runs. The following three runs are for Mach 3.5, density contrast 13:

Hydro

http://www.pas.rochester.edu/~shuleli/triggered/visit_hydro.png

Bx beta=4

http://www.pas.rochester.edu/~shuleli/triggered/visit_bx.png

By beta=4

http://www.pas.rochester.edu/~shuleli/triggered/visit_by.png

The By run has not finished yet. These runs are with lower Mach and higher density contrast still do not form sink particles. For the Hydro and Bx cases, the images are at 1 crushing time, and the simulations actually last till 2 crushing times. We see that Hydro and Bx does not differ much. They seem to stretch quite a lot at about 1 crushing time, which I hope could be solved by the presence of By. This week I will use Boss' original data and see if we can reproduce the collapse he found. From there, we should be able to add magnetic field.

Qual: Wrote the brief for the qual. It has been sent to the committee members last Friday.

Papers: Almost Finished revising the HEDLA proceeding except some figures to tweek. It should be ready in 2 or 3 days.

Resistive Paper: Obtained account on Kraken. will try compiling and running the last two jobs for the resistive paper on it this week.

MHD sink particles: Andy's comment:
I also simply remove mass inside a volume of r ~ 4*dx. Physically this means the gas switches from flux-frozen (or as close to flux-frozen as the code can maintain with finite numerical dissipation) to perfectly resistive inside the sink region. The motivation for this is that the mass to flux ratio in young stars is vastly larger than the mass to flux ratio inferred from observations and in simulations from infrared dark cores. Flux freezing must break down somewhere because observationally only a small fraction of the magnetic flux from the core winds up in the star. Resistive effects, like ambipolar diffusion, it is conjectured, is the dominant effect for this, operating on small scale close to the surface of the protostar. We assume that the magnetic dissipation scale is much, much smaller than the grid scale and therefore throw flux freezing out the window at the smallest scale that we can actually resolve (~ 4 dx). One consequence of doing accretion this way is that flux tubes that get pulled into the sink region become boyant after you remove mass from them, leading to interchange instabilities in the flow. If the assumption of "small scale resistivity" is correct, I believe these interchange instabilities are also correct or, as correct as one can resolve.
​http://adsabs.harvard.edu/abs/2011MNRAS.415.1228P

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