Sink Particles for FLASH

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Sink Particles for FLASH
Robi Banerjee ITA, University of Heidelberg
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Why sink particles?

• modeling of dense regions in collapse
• simulations (e.g. star and cloud formation)
• controlled violation of the Truelove
• criterion (preventing artificial fragmentation
  by
• resolving the Jeans length)
• allows long term runs of star forming regions
• (clusters, binaries, )
• BUT arithmetic part of the simulation
• gt physical interpretation?

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Implementation
Based on Paul Rickers particle module(advancing
of particles, handles boundaries, moves particles
across CPUs/blocks, mapping of grid variables
onto the particles and vice versa)
Extensions / modifications

• creation of particles on the fly
• time dependent particle masses
• mass accretion
• gravity use 1/r2 force for particle
  contribution
• MPI communication for a small number of
• particles

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Implementation

• Gravity

• Solve Poisson equation with for gas distribution
• Compute gravitational acceleration from Fgas
• Add particle contribution to g

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Implementation

• Particle creation

• Conditions by gravitational collapse
• Density criterion ?gas gt ?crit (?crit module
  parameter)
• Check for neighboring particle, i.e. dont create
  a new particle if particle exists within r lt
  raccr
• Check for local gravitational minimum

Note choose ?crit so that Truelove criterion
is not violated, i.e. ?J gt NJ ?xmin
Jeans refinement condition available ( ?J
(pc2/G?)1/2 )
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Implementation

• Mass accretion / momentum transfer

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Implementation

• Inter CPU communication

Use local list of all particles to update
particle properties (adequate for limited number
of sink particles 100 1000)

• Get local list of all sink particles
• Update particle properties locally
• Communicate particle properties

Local all-particle list is also used to
calculate gravitational acceleration
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Test-particle in gaseous potential

• Gas in quasi
• hydrostatic equilibrium
• (Bonnor-Ebert sphere)
• Isolated grav. BCs
• Reflecting hydro BCs
• non-accreting,
• massless particle
• Leapfrog integrator
• Cell-in-Cloud mapping
• of acceleration

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Test-particle in gaseous potential
after 65 orbits (orbital time 6.34
My)excentricity due to varying potential
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Particle-Particle interaction
Test of 1/r2 acceleration
No self-gravity Two Equal mass particles
(orbit setup) Leapfrog integrator
Cell-in-Cloud mapping of acceleration
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Particle-Particle interaction
stable orbits with 1/r2 acceleration
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Collapse of a Bonnor-Ebert sphere

• Mass 9.35 M?
• ?0 1.67x10-20 g cm-3
• Radius 0.39 pc (? 7)
• Sound speed 0.2 km/sec
• tff 5x105 years

• Sink particle properties
• ?crit 1.67x10-16 g cm-3
• 104 ?0
• raccr 1.1x1016 cm
• ?J

e.g. RB, Pudritz Holmes 2004, RB Pudritz
2006, 2007
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Collapse of a Bonnor-Ebert sphere
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Collapse of a Bonnor-Ebert sphere

• asymptodic solution
• ? r-3/2
• (Foster Chevalier 1993,
• Ogino et al. 1999)

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Collapse of a Bonnor-Ebert sphere
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Collapse of a Bonnor-Ebert sphere

• Low threshold run
• ?crit 1.67x10-18 g cm-3
• 100 ?0
• raccr 1.1x1017 cm
• ?J

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Sink particles in action(Formation of Molecular
Clouds)
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Sink particles in action(Formation of Molecular
Clouds)

• So far 14 particles created
• Masses up to 350 M?

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To Do

• a few more tests Boss Bodenheimer
• (Bate Burkert) binary formation
• compare to Shu SIS analytic model
• Bondi-Hoyle accretion in the low density
• regime (Krumholz et al. 2004)
• calculate/store angular momentum
• use for outflows
• use for radiation feedback
• (stellar properties/evolution)