bad_bursters

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.

- [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

- 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

- [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

- [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

Determined to be outside scope of project.
~~
* [ ] 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
~~

1D on a solid surface was successful so the 2D case was the bulk of the project work. The solid case was unstable and resulted in an non-physical explosion. Both the infall and reflective cases were attempted, we found the [] to be optimal. We were able to model a non-viscous and viscous case using hydronamic force and energy equation. Terms for the extremely large B field (10^7-8 T) were not included. Both accreted around the central mass with a large high pressure/empty barrier for the non-viscous case, as the angular momentum is not dissipated. The viscous case correctly accreted on to the surface.

video of non viscous accretion

video of accidental zero pressure accretion

References:

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

(further resources in presentation)

bad_bursters.txt · Last modified: 2014/06/09 13:24 by lauer

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