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mkflowdisk - test particle disk with optional kinematic spirals, based on a flow potential


mkflowdisk out=snapshot [parameters=values ...]


mkflowdisk sets up a two-dimensional disk of test particles in a user-supplied flow potential (in standard potential(5NEMO) format). Optionally the surface density of particles can mimic that of a logarithmic spiral, and thus create a kinematic spiral.

snapmass(1NEMO) and snapcenter(1NEMO) have to be used if for some reason the user want finite mass particles and a perfectly centered set of particles.


The following parameters are recognized in any order if the keyword is also given:
The data are written to this file in SnapShot(5NEMO) format [no default].
Number of disk particles [default: 2048]
name of the potential, see $NEMOOBJ/potential for the current repository. The user can supply his own, see potential(5NEMO) . [default: vrtm51].
Parameters to the user supplied potential. The number of parameters depends on the potential supplied, the first parameter is reserved for a pattern speed. [default: not supplied, parameters are defaulted by how they are defined in the potential(5NEMO) code].
Data_file(s) to the user supplied flow potential. The number of files depends on the potential supplied. It is important the "potential" should be a linear measure of the requested surface density of particles in the disk.
Inner cutoff radius of test-particle disk. [Default: 0.0].
Outer cutoff radius of test-particle disk. [Default: 1.0].
Total mass of the disk. Default: 0.0.
Override the densities from the flow potential and create a uniform disk? Default: f.
Wavenumber of the spiral pattern, such that 2.pi.k.r is the phase of the spiral density maximum. Positive means a trailing spiral pattern. The wavenumber is related to the pitch angle at a given radius: tan(pitch) = 1/(2.pi.k.r). k=0 should be used for an axisymmetric disk. No default.
Note that pitch=0 is not allowed, use k=0 for axisymmetric disks. No default, either k= or pitch= must be used.
Phase offset of the spiral at the outer radius (rmax) of the disk, in degrees. [Default: 0.0]
If used, this will be the integer that is stored in the Key field of a snapshot. Default: not used.
Use random number seed. A zero seed will generate a system-time dependant seed. See xrandom(3NEMO) [default: 0].
Number of output models. [Default: 1].
Change sign of the Z-angular momentum. Is set to -1, it will flip the sign of all velocities are determined from the potential flow. Note that even with sign=1 the disk can have negative angular momentum, since the native angular momentum is determined from the potential. [Default: 1].
In test mode all stars are placed at phase 0, and should thus trace the shape at phase 0 at one arm of spiral. By default particles are spread around phase according to the density distribution as returned by the potential in the flow potential descriptor. Default: f.
Text headline for output file [default: not used].


The current implementation assumes the density is defined along the angular coordinate, since it can currently only do a one-dimensional interpolation. A radial dependance is not possible yet.

See Also

mkspiral(1NEMO) , mkdisk(1NEMO) , snapmass(1NEMO) , snapcenter(1NEMO) , flowcode(1NEMO) , potential(5NEMO)

Update History

18-nov-03    V1.0  created                       PJT
20-nov-03    V1.1 changed some sign conventions    PJT
23-nov-03    V1.3 added key=                PJT
13-dec-03    V1.4 added sign=    PJT

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