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snapspin - add Z-angular momentum or Z-axial outflow to an N-body snapshot


snapspin in=snap_in out=snap_out [parameters=values] ...


snapspin adds angular momentum in the Z-direction to the particles of a snapshot By default, all particles are given the same angular frequency (spin), omega. A positive value means counterclockwise rotation, as seen from the positive Z-axis. If potential and/or forces are present, they are corrected with the usual coriolis term.

Optionally the spin is allowed vary as function of radius, and interpolated from a tabulated rotation curve, V(r). However, the potential and forces cannot be corrected in this case.

Instead of angular momentum, the particles can also be given a Z-axial outflow (or inflow). An outflow curve can optionally also be specified in tabular form, the same way as for spin/rotation. Again, no corrections to potential and forces are made in these cases.

Use snaprotate(1NEMO) to transform to a different spin-axis, and snapshift(1NEMO) to a different center of rotation.


The following parameters are reckognized in any order if the keyword is also given:
Input data is read from snap_in, which must be in standard snapshot(5NEMO) format [no default].
Transformed data is written to snap_out, which will also be in snapshot(5NEMO) format [No default].
The amount of spin (units: velocity per length). If the keyword rotcur (see below) is used, the value of omega is ignored. [default:0].
An ascii table(5NEMO) with radii and velocities in columns 1 and 2 resp. If a table is supplied, the value of omega above is ignored. Between r=0 and the first radius the rotation curve is linearly interpolated, outside the last radius a Keplerian falloff is assumed, and overall interpolation is done using cubic splines (see spline(3NEMO) ). Note: radii in the table must be sorted. Default: none.
The sign of the input rotation curve from r_v_table. Note: Although meant to be +1 or -1, it’s value is simply multiplied with the value interpolated from the input rotation curve. It can also be used in outflow mode, in which case -1 can be used for inflow. [Default: 1].
A boolean flag used to change between spin and outflow mode. By default spin is added to a snapshot (outflow=f).
Only snapshots with time values within times-ranges, which is of the form ts[:te],..., will be copied. [default: all].

See Also

snaprotate(1NEMO) , snapshot(5NEMO)


Peter Teuben


~/src/nbody/trans       snapspin.c

Update History

18-Aug-87    Version 1.0: created              PJT
9-Mar-88    V1.1: data history added    PJT
6-jun-88    V1.2: new filestruct    PJT
25-apr-89    V1.3: get/put_snap, omega bug removed    PJT
22-jul-92    V1.5: added rotcur= and sign=    PJT
1-feb-93    V1.7: fixed phi/acc    PJT
28-apr-98    V2.0: added outflow= for Tony Wong    PJT

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