Table of Contents
mkplummer - generates a snapshot according to a truncated Plummer model
mkplummer constructs a
Plummer model, with a spatial or mass cut-off, after which it performs a
coordinate transformation to the center-of-mass coordinate system. The data
are then written into a file snap-file, in a standard N-body snapshot format.
The model is constructed in VIRIAL units (M=G=-4E=1, with E the total
energy), and finite spatial extent which can be regulated by specifying
mfrac or rfrac or using their default values. The distribution function
of a Plummer model is spherically symmetric and isotropic, and is a polytrope
of index n = 5. See also Aarseth et al. (1974) and Plummer (1911)
is also an implementation in Dehnen’s falcON suite: mkplum(1NEMO)
following parameters are recognized; they may be given in any order.
A non-delta function
mass-spectrum will not create a properly virialized system yet. See snapvirial(1NEMO)
- Output data is written into snapfile, in standard snapshot format.
- Number of particles nobj in Nbody snapshot realization of the Plummer model.
- inner core mass fraction within which no stars will be populated.
- mass fraction of the (infinitely extended) Plummer
model; see rfrac immediately below (Default: rfrac=22.8042468).
- radius fraction of the (infinitely extended) Plummer model. If mfrac = 1.0
then particles will be sprinkled in all over space. If mfrac < 1.0 or rfrac
> 0.0 then each particle is constrained to lie within both the radial and
(cumulative) mass bound. For example, if rfrac( mfrac ) > rfrac then rfrac
is the limiting factor, but if rfrac( mfrac ) < rfrac then mfrac limits
the extent of the Plummer realization. Note: specifying either value may
have no effect if the default value of the other parameter is still the
limiting factor; Beware! (Default: mfrac=0.999; rfrac=22.8042468 , chosen
so that the cumulative mass at rfrac is mfrac).
- seed for the
random number generator (default: a value 0, which will be converted into
a unique new value using UNIX’s clock time, in seconds since once-upon-a-time-in-the-seventies).
- Time at which the snapshot applies (default: time=0.0).
- Reset center of mass to zero? [default: t].
- A scale factor
or scale to virial units (M=G=-4E=1). Use -1 for virial units, and 1 to get
a model in structural (natural) units. Note: large scale factors means small
systems with large velocity disperson. [Default: -1].
- Level of
quit start. 0 is noisy, 1=somewhat quiet, 2=more quiet [default: 0].
- Identification of the mass spectrum. It is normally only a function of mass,
so n(m) will suffice. If nothing specified, all stars will have the same
mass (total mass M=1). [default: not used].
- Expression for
the mass-spectrum. In addition to the mass m from the massname it may contain
any variables contained in the masspars to be specified next. [default:
- List of parameters and their values. They can be
used by name in the massexpr specified before. [default: p,0.0].
- Valid massrange. A lower and higher cutoff must be supplied. The massrange
has arbitrary units, since all masses will be rescaled to set the total
mass M=1. [default: 1,1].
- Optional headline, which is written
as the first item in the snapshot file, the next item being the snapshot
itself. [default: not used].
- Number of models to generate.
Although mostly meant for benchmarks, generating more then 1 model can
be useful to process very large snapshots (which won’t fit in memory) in
a serialized fashion. See also snapsplit. Default: 1.
For very large (>1000) ratio in the mass ranges the spline interpolation,
used in frandom(3NEMO)
, can fail using a valid [0,1] range.
can also be used to create a plummer sphere with a mass spectrum, e.g. a
Salpeter mass spectrum with
% mkplummer salpeter.dat 10000 massname=’n(m)’ massexpr=’pow(m,p)’ masspars=p,-2.35
H.C.Plummer (1911), MNRAS, 71, 460.
S.J. Aarseth, M. Henon and
R. Wielen (1974), Astron. and Astrophys. 37, p. 183.
Piet Hut (Peter
23-Apr-87 Version 1.0: created PIET
10-Jun-88 Version 1.1: created PIET
xx-xxx-88 V1.2: zerocm keyword added PJT
xx-Mar-89 V2.0: full new snapshot version + doc PJT
15-nov-90 V2.3: mass-spectrum and cleanup for NEMO 2.x PJT
6-jun-96 V2.5d: report total mass before scaling PJT
21-mar-04 V2.7: added mlow= PJT+NCM
11-apr-05 V2.8: added nmodel= PJT
15-sep-10 V2.9: clarified rfrac and allow rfrac<0 PJT