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mkdisk - create a uniform-density test disk in an external potential


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


mkdisk sets up a uniform ‘‘cold’’ disk of test particles with positive angular momentum, i.e. rotating counter clockwise (but see sign= below) in the gravitational potential of a user-supplied potential in potential(5NEMO) format.

Optionally an input snapshot can be given, in which case the positions are taken from this input file.

See mktabdisk(1NEMO) for a test disk with more parameters: the density, velocity and dispersion are specified by a table as function of radius.


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 . Currently the potential and total energy are stored in the Potential and Aux slots of the snapshot. [no default].
Number of bodies particles [default: 2048]
name of the potential, see $NEMOOBJ/potential for the current object repository. The user can supply his own, see potential(5NEMO) . [no default].
Paramaters to the user supplied potential. The number of parameters depends on the potential supplied, the first parameter is reserved for the pattern speed. [default: not supplied, parameters as defined by potential(5) ].
Optional data file(s) to the user supplied potential. The number of files depends on the potential supplied. [default: not supplied, or datafile(s) defined by potential(5) ].
Inner cutoff radius of test-particle disk. [Default: 0].
Outer cutoff radius of test-particle disk. [Default: 1].
Total mass of the disk. The default total mass is 0, since this is a testdisk. Since there are a few programs that will not like mass-less particles, this keyword can be used, or snapmass will have to be used before further action is taken. [default: 0].
The fraction that the local velocity dispersion has w.r.t. the local rotation velocity. If a number is given, radial and tangential velocity are by default taken to be the same, with no Z-velocities. If two numbers are given, the first one is the radial dispersion, the second one the tangential (currently wihtout any 2*Omega/Kappa correction), and the Z dispersion 0. Finally, when 3 numbers are given, random motions in Z are also added. [Default: 0]
Use random number seed. If 0 is given, a random number is generated from the time of the day. [default: 0].
Sign of the angular momentum. 1 means counter clockwise rotation in the XY-plane (in case you were wondering, our galaxy has sign=-1). [Default: 1].
Input file, in snapshot(5NEMO) format, of which the positions are used as initial conditions. [Default: not used]. *** lost the implementation **
Normally the particles are distributed randomly in phase, but setting this to true, they will be regularly spread between 0 and TWO_PI. Default: f
A constant radial velocity (>0 means outward motion) added to all particles. Default: 0.
If random motions are added (see frac=), the energy of each particle will change. By setting energy=t the energy is conserved and the "circular" speed will be reduced. This way the guiding center for epicyclic orbits will also be conserved. Note that this only applies to motion in XY. For stars with too much random motion (if frac too high), the random number generator is run again to ensure conserving the planar motion kinetic energy. Default: false.
Use absolute value of velocity dispersion instead of fractional. Default: f
Scaleheight for density dropoff, and circular velocity dropoff. Default: 0,0
(deprecated) Fractional loss in circular streaming as z increased. Use z0_v now.
Text headline for output file [default: not used].

See Also

mktestdisk(1NEMO) , mktabdisk(1NEMO) , mktt72(1NEMO) , mkbaredisk(1NEMO) , snapcenter(1NEMO) , snapfold(1NEMO) , snapspin(1NEMO)

Update History

xx-feb-87    coding, still debugging      PJT
21-Apr-87    V1.0: coding seems OK         PJT
28-Apr-87    V1.1: keyword manss= added    PJT
8-feb-89    V2.0: new implementation using potential(5)    PJT
12-may-90    V3.0: new keywords for potential(5)    PJT
12-mar-91    V4.0: NEMO 2.x        PJT
9-jul-91    corrected a few lies in the documentation    PJT
22-oct-91    V4.1: added in= optional input file          PJT
12-jun-92    V4.2: nbody= is now second parameter, lost in=    PJT
5-may-03    V4.4: added random Z motions by using frac=    PJT
8-may-03    V4.5: added energy=    PJT
13-dec-2017    V4.9: abs,z0,vloss= added    PJT

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