1,914 research outputs found
The Impact of Rotation on Cluster Dynamics
The evolution of rotating, isolated clusters of stars up to core-collapse is
investigated with n-body numerical codes. The simulations start off from
axisymmetric generalisations of King profiles, with added global angular
momentum. In this contribution I report on results obtained for two sets of
single-mass cluster simulations. These confirm the more rapid evolution of even
mildly-rotating clusters. A model is presented with rotational energy
comparable to omega-Centauri's; it reaches core-collapse in less than half the
time required for non-rotating model clusters.Comment: Talk given at the Strasbourg meeting Massive Star Clusters in
November 1999; 7 pages, 3 figures xv-8bit giffed and tarred (= 100Kbytes);
newpasp style file include
The impact of mass loss on star cluster formation. I. Analytic results
We study analytically the disruptive effect of instantaneous gas removal from
a cluster containing O stars.
We setup an iterative calculation based on the stellar velocity distribution
function to compute the fraction of stars that remain bound once the cluster
has ejected the gas and is out of equilibrium. We show that the stellar bound
fraction is a function of the initial cluster distribution function as well as
the star formation efficiency, , taken constant throughout the
cluster.
The case of the Plummer sphere is dealt with in greater details. We find for
this case that up to ~ 50% of the stars may remain bound when
assumes values < 1/2, contrary to expectations derived from the virial theorem.
The fraction of bound stars is expressed algebraically for polytropic
distribution functions.Comment: to appear in M
Evolution of star clusters in arbitrary tidal fields
We present a novel and flexible tensor approach to computing the effect of a
time-dependent tidal field acting on a stellar system. The tidal forces are
recovered from the tensor by polynomial interpolation in time. The method has
been implemented in a direct-summation stellar dynamics integrator (NBODY6) and
test-proved through a set of reference calculations: heating, dissolution time
and structural evolution of model star clusters are all recovered accurately.
The tensor method is applicable to arbitrary configurations, including the
important situation where the background potential is a strong function of
time. This opens up new perspectives in stellar population studies reaching to
the formation epoch of the host galaxy or galaxy cluster, as well as for
star-burst events taking place during the merger of large galaxies. A pilot
application to a star cluster in the merging galaxies NGC 4038/39 (the
Antennae) is presented.Comment: 12 pages, 8 figures. Accepted for publication in MNRA
On the mass function of star clusters
Clusters that form in total 10^3 < N < 10^5 stars (type II clusters) lose
their gas within a dynamical time as a result of the photo-ionising flux from O
stars. Sparser (type I) clusters get rid of their residual gas on a timescale
longer or comparable to the nominal crossing time and thus evolve approximately
adiabatically. This is also true for massive embedded clusters (type III) for
which the velocity dispersion is larger than the sound speed of the ionised
gas. On expelling their residual gas, type I and III clusters are therefore
expected to lose a smaller fraction of their stellar component than type II
clusters. We outline the effect this has on the transformation of the mass
function of embedded clusters (ECMF), which is directly related to the mass
function of star-cluster-forming molecular cloud cores, to the ``initial'' MF
of bound gas-free star clusters (ICMF). The resulting ICMF has, for a
featureless power-law ECMF, a turnover near 10^{4.5} Msun and a peak near 10^3
Msun. The peak lies around the initial masses of the Hyades, Praesepe and
Pleiades clusters. We also find that the entire Galactic population II stellar
spheroid can be generated if star formation proceeded via embedded clusters
distributed like a power-law MF with exponent 0.9 < beta < 2.6.Comment: 10 pages, 4 figures, accepted by MNRAS, small adjustments for
consistency with published versio
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