The CosmicBEAR and the StarWind

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The CosmicBEAR and the StarWind

• Presenter Paul Edmon
• Graduate Student Colloquium
• 9-24-08

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The CosmicBEAR and the StarWind
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Outline

• Brief Introduction
• Current Research
• Stellar Winds and Particle Acceleration
• CosmicBEAR

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Introduction

• Hometown Seattle, WA
• 5th Year Graduate Student
• Adviser Tom Jones
• Currently ABD
• Office Walter 415

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Current Research

• General Topic Numerical Modeling of Particle
  Acceleration and Radiative Processes in
  Astrophysical Shocks
• Projects
• CosmicBEAR Code for Ph.D. Project
• Particle Acceleration in Stellar Winds from High
  Mass Stars Ph.D. Project
• Evolution of Stellar Winds from Low Mass Stars
• Nonthermal Radiation from Type Ia Supernovae
  Continuation of 2nd Year Project
• Gamma Rays from IC off of Pairs produced from
  UHECR interaction with EBL
• AstroBEAR Code Development

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Stellar Winds

• Outflows from Stars
• De Laval Nozzle
• Drivers
• Gas Pressure Sun
• Radiative Pressure
• Dust RGB Stars
• Lines O, WR Stars
• Alfvén Waves?

Credit Jacobs Rocketry
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Solar Wind
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O Stars and WR Stars

• O Star
• Main Sequence
• Mass 20-100 M?
• Temperature 40,000 K
• Luminosity 500,000 L?
• Lifetime 3 Myr
• Mass Loss Rate 10-6 M?/yr
• Wind Velocity 3000-4000 km/s

• Wolf-Rayet Star
• Evolved O Stars (WC, WN)
• Mass 20-50 M?
• Temperature 25,000-50,000K
• Luminosity 1,000,000 L?
• Lifetime 100 kyr
• Mass Loss Rate 10-5 M?/yr
• Wind Velocity 2000 km/s

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Nonthermal Radio, X-ray and TeV Emission

• Radio
• Emission Seen from about a quarter of O and WR
  Stars
• Synchrotron Emission
• X-Ray
• Thought to be Emission from WR Stars in Certain
  Cases
• Inverse Compton
• TeV Gamma-Rays
• TeV Emission Seen in Young Star Clusters and
  Single WR Stars
• IC or Pion Decay

Credit HESS page on Westerlund 2
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Diffusive Shock Acceleration (DSA)

• Model
• A thermal population of protons enter the shock
• Protons from the high energy tail diffuse through
  the shock scattering off of Alfvén waves
• Maximum possible accelerated energy is limited by
  the physical extent of the system and gyroradius
  of the proton

u1
u2
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Shocks

• What type of shock is producing the particle
  population?
• Internal Shocks Instabilities in the Wind
• Termination Shock Interaction with Interstellar
  Medium (ISM)
• Colliding Wind Shock Binary Interaction

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Current State of the Art

• Dougherty Williams (2000) Non-thermal emitting
  WR Stars are Binaries with Colliding Winds
• Van Loo et.al. (2005, 2006)
• 1-D Hydro with no electron reacceleration
• Emission can be explained by
• Single Strong Shock
• Multiple Strong Shocks
• For Multiple Strong Shocks the shock strength
  falls off with radius which leads to the wrong
  spectral index, plus a lot of shocks are needed
• Van Loo favors colliding wind scenario similar to
  WR stars

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Requests from the Community

• Pittard Dougherty (2006)
• Actual DSA modeling for these systems
• How much preshock energy goes into the particles
• Model should include losses
• Outstanding Questions
• Is the efficiency of particle acceleration high
  enough for shock modification to occur?
• Are particles reaccelerated in wind embedded
  shocks?
• What effect does anisotropic winds have on
  colliding winds?

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Plan

• Develop 2-D Magnetohydrodynamic (MHD) Code that
  includes DSA with losses
• Model DSA and Emissions from a single O and WR
  Star
• Do the same for a Colliding Wind Scenario

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Execution

• 2-D MHD Solver AstroBEAR
• DSA Solver CGMV
• AstroBEARCGMV ? CosmicBEAR
• Emissions Cosmicp

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AstroBEAR

• Astronomical Boundary Embedded Adaptive
  Refinement
• MUSCL Solver
• Adaptive Mesh Refinement
• Uses Constrained Transport for MHD
• Developed by Sorin Mitran (UNC) and Adam Franks
  Group (University of Rochester) with some help
  from Tom

Credit Lawrence Berkeley National Lab
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AstroBEAR Solar Wind
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CGMV

• CGMV Coarse Grained finite Momentum Volume
  (Jones Kang 2005)
• Solves the Diffusion-Convection equation with an
  order of magnitude less bins
• Takes advantage of the fact that the particle
  spectrum is going to be a power-law
• Works with the first two moments of the
  Diffusion-Convection equation
• Scheme
• Crank-Nicholson
• Implicit Unconditionally Stable
• May not work well with AMR
• Explicit
• Conditionally Stable Time step constrained by
  shortest diffusion time.
• Works with AMR

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CosmicBEAR

• Goals
• Successfully Merge AstroBEAR and CGMV
• Make CR step execution time close to or equal to
  the MHD step execution time
• Add in corrections for Cylindrical Geometry
• Verify Code
• Start doing Science!
• Current Status
• Code successfully merged but new CR solver needs
  to be implemented

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Summary

• Stellar Winds
• Single Wind vs. Colliding Wind
• Shock Modification?
• 1-D vs. 2-D
• CosmicBEAR
• Parallel 2-D MHD-DSA AMR code