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Name

mkh41 - Create a Holmberg 1941 disk

Synopsis

mkh41 [parameter=value]

Description

mkh41 creates a disk of particles similar to the one used in Holmberg’s 1941 paper (1941ApJ....94..385H). Currently each ring is placed in a separate snapshot. Use snapmerge(1NEMO) if they must be in a single snapshot.

The disk is rotating counter clock wise by default, but with totally fake velocities. See the example below to assign more realistic velocities.

The disk quoted in the 1941 paper has a mass of 10^11 solar masses, and a diameter of 2300 pc.

Parameters

The following parameters are recognized in any order if the keyword is also given:
out=
output file name, each ring will be in a separate snapshot(5NEMO) . Use snapmerge(1NEMO) to merge the rings into a single snapshot. No Default.
nbody=
number of particles for each ring. [Default: 1,6,8,10,12]
radius=
radii of rings. The number of rings must match that of nbody=. [Default: 0,1,2,3,4]
mass=
Mass of a particle in each ring. The number of rings must match that of nbody=. [Default: 1.0,1.0,1.0,0.7,0.3]
phi=
The position angle of the first particle in each ring, 0 being along the Y axis to match the H41 disk as shown in Fig 3b. The number of rings must match that of nbody=. [Default: 0,0,0,0,0]
sign=-1|1
Sign of the angular momentum. 1 means counter clockwise rotation. [Default: 1].
headline=
verbiage for output []

Caveat

It is hard to create the exact same initial conditions as in the H41 paper, as not enough details are provided. Also, Figure 4a/b seem to suggest that the inner 7 points are not even acted upon self consistently, but just following the path of the galaxy.

A set of French Curves is not used for this program.

Examples

Since this program does not properly compute rotational velocities, and because each ring is in a separate snapshot, it is somewhat cumbersome to create the actual initial conditions for a true Holmberg 1941 disk:
mkh41 -  |
  snapmerge - - |
  snapcenter - - m |
  hackforce - - tol=0.001 fcells=2 |
  snapdisk - h41.in

See Also


mkconfig(1NEMO), mktt72(1NEMO), mkdisk(1NEMO), snapscale(1NEMO), snapstack(1NEMO)
Holmberg, E. (1941) -  On the clustering tendencies among the nebulae. ApJ.
94, 385.

Lindblad, P.O. (1960) - The development of spiral structure in a galaxy approached
by numerical computations
http://adsabs.harvard.edu/abs/1960StoAn..21....4L

Author

Peter Teuben, Alar Toomre

Update History


15-Jul-2009    V1.0 Created at PiTP (IAS @ Princeton)    PJT + AT
22-jul-2009    V1.1 added sign=    PJT


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