239 research outputs found
Star cluster dynamics
Dynamical evolution plays a key role in shaping the current properties of
star clusters and star cluster systems. A detailed understanding of the effects
of evolutionary processes is essential to be able to disentangle the properties
which result from dynamical evolution from those imprinted at the time of
cluster formation. In this review, we focus our attention on globular clusters
and review the main physical ingredients driving their early and long-term
evolution, describe the possible evolutionary routes and show how cluster
structure and stellar content are affected by dynamical evolution.Comment: 20 pages, 2 figures. To appear as invited review article in a special
issue of the Phil. Trans. Royal Soc. A: Ch. 7 "Star clusters as tracers of
galactic star-formation histories" (ed. R. de Grijs). Fully peer reviewed.
LaTeX, requires rspublic.cls style fil
XHIP-II: Clusters and associations
Context. In the absence of complete kinematic data it has not previously been
possible to furnish accurate lists of member stars for all moving groups. There
has been an unresolved dispute concerning the apparent inconsistency of the
Hipparcos parallax distance to the Pleiades.
Aims. To find improved candidate lists for clusters and associations
represented among Hipparcos stars, to establish distances, and to cast light on
the Pleiades distance anomaly.
Methods. We use a six dimensional fitting procedure to identify candidates,
and plot CMDs for 20 of the nearest groups. We calculate the mean parallax
distance for all groups.
Results. We identify lists of candidates and calculated parallax distances
for 42 clusters and 45 associations represented within the Hipparcos catalogue.
We find agreement between parallax distance and photometric distances for the
most important clusters. For single stars in the Pleiades we find mean parallax
distance 125.6 \pm 4.2 pc and photometric distance 132 \pm 3 pc calibrated to
nearby groups of similar in age and composition. This gives no reason to doubt
either the Hipparcos database or stellar evolutionary theory.Comment: Accepted for publication in Astronomy Letters, 10 pages, 2 fig
New catalogue of optically visible open clusters and candidates
We have compiled a new catalogue of open clusters in the Galaxy which updates
the previous catalogues of Lynga (1987) and of Mermilliod (1995) (included in
the WEBDA database). New objects and new data, in particular, data on
kinematics (proper motions) that were not present in the old catalogues, have
been included. Virtually all the clusters (1537) presently known were included,
which represents an increment of about 347 objects relative to the Lynga (1987)
catalogue. The catalogue is presented in a single table containing all the
important data, which makes it easy to use. The catalogue can be accessed on
line either at http://www.iagusp.usp.br/~wilton/ or as an electronic table
which will be made available at the CDS.Comment: 3 pages, submitted to A&
Dissolving star cluster candidates
We present a list of 34 neglected entries from star cluster catalogues
located at relatively high galactic latitudes ( 15) which
appear to be candidate late stages of star cluster dynamical evolution.
Although underpopulated with respect to usual open clusters, they still present
a high number density contrast as compared to the galactic field. This was
verified by means of (i) predicted model counts from different galactic
subsystems in the same direction, and (ii) Guide Star Catalog equal solid angle
counts for the object and surrounding fields. This suggests that the objects
are physical systems, possibly star clusters in the process of disruption or
their fossil remains. The sample will be useful for followup studies in view of
verifying their physi cal nature.Comment: manuscript in LATEX with 7 pages, 7 figures .ps Accepted for
Astronomy and Astrophysics main journa
The evolution of luminosity, colour and the mass-to-luminosity ratio of Galactic open clusters: comparison of discrete vs. continuous IMF models
(abridged) We found in previous studies that standard Simple Stellar
Population (SSP) models are unable to describe or explain the colours of
Galactic open clusters both in the visible and in the NIR spectral range. (...)
We construct a numerical SSP-model, with an underlying Salpeter IMF, valid
within an upper and lower stellar mass range, and with total masses
typical of open clusters. We assume that the mass
loss from a cluster is provided by mass loss from evolved stars and by the
dynamical evaporation of low-mass members due to two-body relaxation. The data
for the latter process were scaled to the models from high-resolution N-body
calculations. We also investigate how a change of the -limit influences
magnitudes and colours of clusters of a given mass and derive a necessary
condition for a luminosity and colour flash. The discreteness of the IMF leads
to bursts in magnitude and colour of model clusters at moments when red
supergiants or giants appear and then die. The amplitude of the burst depends
on the cluster mass and on the spectral range; it is strongly increased in the
NIR compared to optical passbands. In the discrete case, variations of the
parameter are able to substantially change the magnitude-age and
-age relations. For the colours, the lowering of considerably
amplifies the discreteness effect. The influence of dynamical mass loss on
colour and magnitude is weak, although it provides a change of the slopes of
the considered relations, improving their agreement with observations. For the
Galactic open clusters we determined luminosity and tidal mass independent of
each other. The derived mass-to-luminosity ratio shows, on average, an increase
with cluster age in the optical, but gradually declines with age in the NIR.
The observed flash statistics can be used to constrain in open clusters.Comment: 15 pages, 13 figures, accepted for publication in Astronomy and
Astrophysic
New SPB stars in the field of the young open cluster NGC 2244 discovered by the MOST photometric satellite
During two weeks of nearly continuous optical photometry of the young open
cluster NGC 2244 obtained by the MOST satellite, we discovered two new SPB
stars, GSC 00154-00785 and GSC 00154-01871. We present frequency analyses of
the MOST light curves of these stars, which reveal two oscillation frequencies
(0.61 and 0.71 c/d) in GSC 00154-00785 and two (0.40 and 0.51 c/d) in GSC
00154-01871. These frequency ranges are consistent with g-modes of excited in models of main-sequence or pre-main-sequence (PMS) stars of
masses 4.5 - 5 and solar composition .
Published proper motion measurements and radial velocities are insufficient to
establish unambiguously cluster membership for these two stars. However, the
PMS models which fit best their eigenspectra have ages consistent with NGC
2244. If cluster membership can be confirmed, these would be the first known
PMS SPB stars, and would open a new window on testing asteroseismically the
interior structures of PMS stars.Comment: accepted for publication in MNRA
N-body simulations of gravitational dynamics
We describe the astrophysical and numerical basis of N-body simulations, both
of collisional stellar systems (dense star clusters and galactic centres) and
collisionless stellar dynamics (galaxies and large-scale structure). We explain
and discuss the state-of-the-art algorithms used for these quite different
regimes, attempt to give a fair critique, and point out possible directions of
future improvement and development. We briefly touch upon the history of N-body
simulations and their most important results.Comment: invited review (28 pages), to appear in European Physics Journal Plu
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