| | 3 | |
| | 4 | |
| | 5 | == Computational Setup == |
| | 6 | |
| | 7 | We would like to understand how different parameters and environments can shape planetary nebulae. In order to do this, we set up several simulations of different types of flows in various ambient media. We initialize the grid with the following environments: [[BR]] |
| | 8 | * '''Constant Ambient:''' The entire grid starts with a constant density of 300 particles/cm^3^ |
| | 9 | * '''Stratified Ambient:''' The density decays as 1/r^2^ radially from a central value of 300 particles/cm^3^ |
| | 10 | * '''Toroidal Ambient:''' The density decays smoothly from equator to pole from a seed value of 300 particles/cm^3^ using the function described in [http://adsabs.harvard.edu/abs/1994ApJ...430..800F Frank & Mellema, 1994 ApJ]. The two parameters used are [[latex($\alpha_{t}$)]], which determines the density contrast from the pole to equator, and [[latex($\beta_{t}$)]], which determines how elliptical or spherical the distribution is. |
| | 11 | |
| | 12 | [[BR]] |
| | 13 | |
| | 14 | For each ambient, we introduce three different types of flows: |
| | 15 | |
| | 16 | * '''Clump:''' A spherical cloud of gas with radius 500 AU travels at 200 km/s with initial density 40,000 particles/cm^3^. |
| | 17 | * '''Jet: ''' A jet with radius 500 AU and density 40,000 particles/cm^3^ injects gas into the grid from below with initial velocity 200 km/s along the y axis. |
| | 18 | * '''Diverging Wind: ''' This is the same setup as the jet, but instead of injecting gas directly along the y axis, it will sweep an arc of 10^o^. |
| | 19 | |
| | 20 | We also introduce toroidal magnetic fields in the MHD runs, which are initialized off the grid, according to the specifications in [http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1989ApJ...344...89L Lind et. al, 1989 ApJ]. We choose Rm = .6Rjet, or 300 AU, based on previous papers. This parameter measures how electric current flows along the jet. To determine initial field strength, we use the magnetic [[latex($\beta$)]] (not to be confused with [[latex($\beta_{t}$)]] which is associated with the shape of the torus), which is the ratio of the thermal pressure to the magnetic pressure. High values of [[latex($\beta$)]] will mean weak magnetic fields. For our initial runs, we chose [[latex($\beta = 1$)]]. |
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