Issue |
A&A
Volume 441, Number 1, October I 2005
|
|
---|---|---|
Page(s) | 117 - 129 | |
Section | Galactic structure, stellar clusters, and populations | |
DOI | https://doi.org/10.1051/0004-6361:20042241 | |
Published online | 13 September 2005 |
An analytical description of the disruption of star clusters in tidal fields with an application to Galactic open clusters
1
Astronomical Institute, Utrecht University, Princetonplein 5, 3584CC Utrecht, The Netherlands e-mail: [lamers;bastian;gieles]@astro.uu.nl
2
SRON Laboratory for Space Research, Sorbonnelaan 2, 3584CC Utrecht, The Netherlands
3
Sternwarte, University of Bonn, Auf dem Hügel 71, 53121 Bonn, Germany e-mail: holger@astro.uni-bonn.de
4
Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany e-mail: nkharchenko@aip.de
5
Astronomisches Rechen-Institut, Mönchhofstraße 12-14, 69120 Heidelberg, Germany e-mail: nkhar@ari.uni-heidelberg.de
6
Main Astronomical Observatory, 27 Academica Zabolotnogo Str., 03680 Kiev, Ukraine e-mail: nkhar@mao.kiev.ua
7
Astronomical Institute, University of Amsterdam, Kruislaan 403, 1098SJ Amsterdam, The Netherlands e-mail: spz@science.uva.nl
8
Informatics Institute, University of Amsterdam, Kruislaan 403, 1098SJ Amsterdam, The Netherlands
Received:
23
October
2004
Accepted:
26
May
2005
We present a simple analytical description of the disruption of star
clusters in a tidal field.
The cluster disruption time, defined as tdis,
depends on the mass M of the cluster as
tdis with for clusters in a
tidal field, as shown by
empirical studies of cluster samples in different galaxies
and by N-body simulations.
Using this simple description we derive an analytic expression
for the way in which the mass of a cluster decreases with time due to
stellar evolution and disruption.
The result agrees very well with those of detailed N-body simulations for clusters in the tidal field of our galaxy.
The analytic expression can be used to predict the mass and age
histograms of surviving clusters for any cluster initial mass function
and any cluster formation history.
The method is applied to explain the age distribution of the
open clusters in the solar neighbourhood within 600 pc, based on a new
cluster sample that appears to be unbiased
within a distance of about 1 kpc. From a comparison between the
observed and predicted age distributions in the age range between 10 Myr to
3 Gyr we find the following results:
(1) The disruption time of a 104
cluster in the solar
neighbourhood is about
Gyr.
This is a factor of 5 shorter than that derived from N-body simulations
of clusters in the tidal field of the galaxy. Possible reasons for
this discrepancy are discussed.
(2) The present star formation rate in bound clusters
within 600 pc of the Sun is
Myr-1,
which corresponds to a surface star formation rate of bound clusters
of
yr-1 pc-2.
(3) The age distribution of open clusters shows a bump between 0.26 and 0.6 Gyr when the cluster formation rate was 2.5 times higher
than before and after.
(4) The present star formation rate in bound
clusters is about half that derived from the
study of embedded clusters.
The difference suggests that about half of the clusters in the solar
neighbourhood become unbound within about 10 Myr.
(5) The most massive clusters within 600 pc had an initial
mass of about
. This is in agreement with
the statistically expected value based on a cluster initial mass function
with a slope of -2, even if the physical upper mass limit for cluster
formation is as high as 106
.
Key words: Galaxy: globular clusters: general / Galaxy: halo / Galaxy: kinematics and dynamics / Galaxy: open clusters and associations: general / Galaxy: solar neighbourhood / galaxies: star clusters
© ESO, 2005
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