98 research outputs found
Monte Carlo simulations of star clusters - II. Tidally limited, multi-mass systems with stellar evolution
A revision of Stod\{'o}{\l}kiewicz's Monte Carlo code is used to simulate
evolution of large star clusters. A survey of the evolution of N-body systems
influenced by the tidal field of a parent galaxy and by stellar evolution is
presented. The results presented are in good agreement with theoretical
expectations and the results of other methods (Fokker-Planck, Monte Carlo and
N-body). The initial rapid mass loss, due to stellar evolution of the most
massive stars, causes expansion of the whole cluster and eventually leads to
the disruption of less bound systems (). Models with larger
survive this phase of evolution and then undergo core collapse and subsequent
post-collapse expansion, like isolated models. The expansion phase is
eventually reversed when tidal limitation becomes important. The results
presented are the first major step in the direction of simulating evolution of
real globular clusters by means of the Monte Carlo method.Comment: 13 pages, 18 figures, 3 tables, submitted to MNRA
Monte-Carlo Simulations of Star Clusters I. First Results
A revision of Stodolkiewicz's Monte-Carlo code is used to simulate evolution
of star clusters. The new method treats each superstar as a single star and
follows the evolution and motion of all individual stellar objects. The first
calculations for isolated, equal-mass N-body systems with three-body energy
generation according to Spitzer's formulae show good agreement with direct
N-body calculations for N=2000, 4096 and 10000 particles. The density,
velocity, mass distributions, energy generation, number of binaries etc. follow
the N-body results. Only the number of escapers is slightly too high compared
to N-body results and there is no level off anisotropy for advanced
post-collapse evolution of Monte-Carlo models as is seen in N-body simulations
for N 10000 gravothermal oscillations are
clearly visible. The calculations of N=2000, 4096, 10000, 32000 and 100000
models take about 2, 6, 20, 130 and 2500 hours, respectively. The Monte-Carlo
code is at least 10^5 times faster than the N-body one for N=32768 with
special-purpose hardware (Makino 1996ab). Thus it becomes possible to run
several different models to improve statistical quality of the data and run
individual models with N as large as 100000. The Monte-Carlo scheme can be
regarded as a method which lies in the middle between direct N-body and
Fokker-Planck models and combines most advantages of both methods.Comment: 11 pages, 8 PS-figures, To appear in MNRA
COCOA Code for Creating Mock Observations of Star Cluster Models
We introduce and present results from the COCOA (Cluster simulatiOn
Comparison with ObservAtions) code that has been developed to create idealized
mock photometric observations using results from numerical simulations of star
cluster evolution. COCOA is able to present the output of realistic numerical
simulations of star clusters carried out using Monte Carlo or \textit{N}-body
codes in a way that is useful for direct comparison with photometric
observations. In this paper, we describe the COCOA code and demonstrate its
different applications by utilizing globular cluster (GC) models simulated with
the MOCCA (MOnte Carlo Cluster simulAtor) code. COCOA is used to synthetically
observe these different GC models with optical telescopes, perform PSF
photometry and subsequently produce observed colour magnitude diagrams. We also
use COCOA to compare the results from synthetic observations of a cluster model
that has the same age and metallicity as the Galactic GC NGC 2808 with
observations of the same cluster carried out with a 2.2 meter optical
telescope. We find that COCOA can effectively simulate realistic observations
and recover photometric data. COCOA has numerous scientific applications that
maybe be helpful for both theoreticians and observers that work on star
clusters. Plans for further improving and developing the code are also
discussed in this paper.Comment: 18 pages, 12 figures, accepted for publication in MNRAS. Revised
manuscript has a new title, better quality figures and many other
improvements. COCOA can be downloaded from: https://github.com/abs2k12/COCOA
(comments are welcome
Comparing Direct N-Body Integration with Anisotropic Gaseous Models of Star Clusters
We compare the results for the dynamical evolution of star clusters derived
from anisotropic gaseous models with the data from N-body simulations of
isolated and one-component systems, each having modest number of stars. The
statistical quality of N-body data was improved by averaging results from many
N-body runs, each with the same initial parameters but with different sequences
of random numbers used to initialize positions and velocities of the particles.
We study the development of anisotropy, the spatial evolution and energy
generation by three-body binaries and its N-dependence. We estimate the
following free parameters of anisotropic gaseous models: the time scale for
collisional anisotropy decay and the coefficient in the formulae for energy
generation by three-body binaries. To achieve a fair agreement between N-body
and gaseous models for the core in pre- as well as in post-collapse only the
energy generation by binaries had to be varied by N. We find that anisotropy
has considerable influence on the spatial structure of the cluster particularly
for the intermediate and outer regions.Comment: 24 pages (25 figures appended as postsript files
Cataclysmic variables in Globular clusters: First results on the analysis of the MOCCA simulations database
In this first investigation of the MOCCA database with respect to cataclysmic
variables, we found that for models with Kroupa initial distributions,
considering the standard value of the efficiency of the common-envelope phase
adopted in BSE, no single cataclysmic variable was formed only via binary
stellar evolution, i. e., in order to form them, strong dynamical interactions
have to take place. Our results also indicate that the population of
cataclysmic variables in globular clusters are, mainly, in the last stage of
their evolution and observational selection effects can change drastically the
expected number and properties of observed cataclysmic variables.Comment: 4 pages, 3 figures. Presented at the MODEST 16/Cosmic Lab conference
in Bologna, Italy, April 18-22 2016. To be pusblished in Mem. S. A. It.
Conference Serie
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