We have decided to analyze the accretion onto a neutron star just up until the hydrogen burning begins. We'll first attempt this as an adaptation to the Bondi accretion problem with a solid sphere near the origin (also relevant to the problem of infall onto the proto-neutron star during core collapse). If we're successful, we'll try an accretion disk in 2D with polar geometry.

• Input Person (Sarah Schwartz)
  • [X] X-ray bursts
    • [X] Accretion rate ~ 10^-8 Solar Mass / yr
    • [X] Radius ~ 10-15 km
    • [X] Mass ~ 1 Solar Mass
  • [X] Novae
    • [X] Accretion rate ~ 10^-9 Solar Mass / yr
    • [X] Radius ~ 10^4 km
    • [X] Mass ~ 1 Solar Mass
  • [ ] Density of in falling material
  • [X] Alpha parameter = 0<alpha<1
• Code Person (Justin Brown)
  • 2D
    • [X] Get the VH-1 polar model working.
      • Set ngeomx = 1 (radial cylindrical), ngeomy = 3 (theta), nlefty = 3, nrighty = 3 (periodic)
    • [X] Set up accretion
      • Set nrightx = 2 (constant inflow), uotflo * rotflo * outer area of simulation (2 * pi * xmas) = 1
      • Set votflo to be the desired velocity at the boundary edge
    • [X] Implement gravity
      • In forces, set grav (n) under sweep “x”, cylindrical to be -GM/xao(n)**2
    • [X] Implement a viscosity model.
      • We're choosing to use the derivative in the radial direction of only the tangential coordinate
        • alpha*1/r(dv/dr)+alpha*d2v/dr2
      • In forces, set grav (n) under sweep “y”, cylindrical angle to the above expression
    • [X] Run Models
      • [X] Non-dimensionalize
        • The length unit is the radius of the neutron star, R_ns
        • The time unit is sqrt (R_ns^3/GM_ns)
        • The mass unit is M'sqrt (R_ns^3/GM_ns), where M' is the mass infall rate
      • [X] Determine free parameters
        • Outer radius of simulation, xmax
        • Infall velocity, uotflo
        • Viscosity, alpha
        • Tangential initial velocity, votflo
      • [X] Run models with uotflo = -0.1, votflo = 0.2, xmax = 10.0
        • [X] Viscid (alpha = 1.0)
        • [X] Semi-Viscid (alpha = 0.1)
        • [X] Inviscid (alpha = 0.0)
      • [] Run models with uotflo = -1.0, votflo = 0.2, xmax = 10.0
• Analysis Person (Amber Lauer)
  • [x] Get visualization working
    • [x] Install NetCDF
      • visit on ubuntu/linux was a quagmire, went with windows virtualbox installation :(
  • [x] Gathering the initial conditions for novae and X-ray bursts
    • have average values for NS and WD, time permitting will constrain to single case and derive from scratch

*[x] PRESENTATION

• [x] Outline concepts and highlight theory for presentation
• [x] Encode .cdf data to video for presentation
• [x] Compile references for presentation
• [x] Compile images for presentation

XX * [ ] Determine the input abundances

• [ ] Build the nuclear network for the problem
• [ ] Take output from the codes
  • [ ]determine when hydrogen burning begins
  • [ ]analyze data values to optimize scale(linear vs log) and ranges(0-?) for visualization

XX

 Above determined to be outside scope of project.
 
 

Link to Code on GitHub: External Link

Parameter sources

• Accretion Power in Astrophysics - Frank, King, Raine
• Accretion Disk for Beginners : External Link (Notes PDF)