514 research outputs found
The embedded cluster or association Trumpler 37 in IC1396: a search for evolutionary constraints
It is currently widely accepted that open star clusters and stellar
associations result from the evolution of embedded star clusters. Parameters
such star formation efficiency, time-scale of gas removal and velocity
dispersion can be determinants of their future as bound or unbound systems.
Finding objects at an intermediate evolution state can provide constraints to
model the embedded cluster evolution. In the HII region IC1396, Trumpler 37 is
an extended young cluster that presents characteristics of an association. We
employed the Two Micron All Sky Survey (2MASS) photometry to analysing its
structure and stellar content, and determining its astrophysical parameters. We
also analysed 11 bright-rimmed clouds in IC1396 in order to search for young
infrared star clusters, and the background open star cluster Teutsch 74, to
verify whether it has any contribution to the observed stellar density profile
of Trumpler 37. The derived parameters and comparison with template objects
from other studies lead us to conclude that Trumpler 37, rather than as a star
cluster, will probably emerge from its molecular cloud as an OB association.Comment: 13 pages, 10 figures, 6 table
Near-infrared study of new embedded clusters in the Carina complex
We analyse the nature of a sample of stellar overdensities that we found
projected on the Carina complex. This study is based on 2MASS photometry and
involves the photometry decontamination of field stars, elaboration of
intrinsic colour-magnitude diagrams J(J-Ks), colour-colour diagrams
(J-H)(H-Ks) and radial density profiles, in order to determine the
structure and the main astrophysical parameters of the best candidates. The
verification of an overdensity as an embedded cluster requires a CMD consistent
with a PMS content and MS stars, if any. From these results, we are able to
verify if they are, in fact, embedded clusters. The results were, in general,
rewarding: in a sample of 101 overdensities, the analysis provided 15
candidates, of which three were previously catalogued as clusters
(CCCP-Cl16, Treasure Chest and FSR1555), and the 12 remaining are
discoveries that provided significant results, with ages not above 4.5Myr
and distances compatible with the studied complex. The resulting values for the
differential reddening of most candidates were relatively high, confirming that
these clusters are still (partially or fully) embedded in the surrounding gas
and dust, as a rule within a shell. Histograms with the distribution of the
masses, ages and distances were also produced, to give an overview of the
results. We conclude that all the 12 newly found embedded clusters are related
to the Carina complex.Comment: 10 pages, 14 figures, accepted for publication in MNRA
Star clusters in the Sh2-132 complex: clues about the connection between embedded and open clusters
Embedded clusters are formed in molecular clouds where massive stars can
produce HII regions. The detailed embedded-open cluster evolutionary connection
as well as the origin of associations are yet to be unveiled. There appears to
be a high infant mortality rate among embedded clusters and the few survivors
evolve to open clusters. We study the colour-magnitude diagrams and structure
of the star clusters related to the Sh2-132 HII region using the 2MASS
database. Cluster fundamental and structural parameters are determined via MS
and PMS isochrones and stellar radial density profiles. We report the discovery
of four clusters. One of them is projected a few diameters away from the
optical cluster Teutsch\,127 and appears to be deeply embedded, seen only in
the infrared. Evidence is found that we are witnessing the dynamical transition
from an embedded to an open cluster. An additional cluster is also close to
Teutsch\,127 and might be associated with a bow-shock. We also study the CMD
and structure of the open cluster Berkeley\,94 in Sh2-132 and a new cluster
which is projected in the outskirts of the complex. Finally, we searched for
star clusters around the two known Wolf-Rayet stars in the complex. One of them
appears to be related to a compact cluster. Finally, the present analyses
suggest early dynamical evolution for young star clusters.Comment: 12 pages, 20 figures, 6 table
Structures in surface-brightness profiles of LMC and SMC star clusters: evidence of mergers?
The LMC and SMC are rich in binary star clusters, and some mergers are
expected. It is important to characterize single clusters, binary clusters and
candidates to mergers. We selected a sample of star clusters in each Cloud with
this aim. Surface photometry of 25 SMC and 22 LMC star clusters was carried
with the ESO Danish 1.54 m telescope. 23 clusters were observed for the first
time for these purposes. We fitted Elson, Fall and Freeman (1987, EFF) profiles
to the data, deriving structural parameters, luminosities and masses. We also
use isophotal maps to constrain candidates to cluster interactions.} {The
structural parameters, luminosities and masses presented good agreement with
those in the literature. Three binary clusters in the sample have a double
profile. Four clusters (NGC 376, K 50, K 54 and NGC 1810) do not have
companions and present as well important deviations from EFF profiles. The
present sample contains blue and red Magellanic clusters. Extended EFF profiles
were detected in some blue clusters. We find evidence that important deviations
from the body of EFF profiles might be used as a tool to detect cluster
mergers.Comment: 16 pages and 8 figures. Accepted by A&
Photometry and dynamics of the minor mergers AM\,1228-260 and AM\,2058-381
We investigate interaction effects on the dynamics and morphology of the
galaxy pairs AM\,2058-381 and AM\,1228-260. This work is based on images
and long-slit spectra obtained with the Gemini Multi-Object Spectrograph at the
Gemini South Telescope. The luminosity ratio between the main (AM\,2058A) and
secondary (AM\,2058B) components of the first pair is a factor of 5,
while for the other pair, the main (AM\,1228A) component is 20 times more
luminous than the secondary (AM\,1228B). The four galaxies have pseudo-bulges,
with a S\'ersic index . Their observed radial velocities profiles (RVPs)
present several irregularities. The receding side of the RVP of AM\,2058A is
displaced with respect to the velocity field model, while there is a strong
evidence that AM\,2058B is a tumbling body, rotating along its major axis. The
RVPs for AM\,1228A indicate a misalignment between the kinematic and
photometric major axes. The RVP for AM\,1228B is quite perturbed, very likely
due to the interaction with AM\,1228A. NFW halo parameters for AM\,2058A are
similar to those of the Milky Way and M\,31. The halo mass of AM\,1228A is
roughly 10\% that of AM\,2058A. The mass-to-light (M/L) of AM\,2058 agrees with
the mean value derived for late-type spirals, while the low M/L for AM\,1228A
may be due to the intense star formation ongoing in this galaxy.Comment: 20 pages, 10 figures, accepted for publication in MNRA
Probing Mass Segregation in NGC 6397
In this study, we present a detailed study of mass segregation in the
globular clister NGC 6397. First, we carry out a photometric analysis of
projected ESO-VLT data (between 1 and 10 arcmin from the cluster centre),
presenting the luminosity function corrected by completeness. The luminosity
function shows a higher density of bright stars near the central region of the
data, with respect to the outer region. We calculate a deprojected model
(covering the whole cluster) estimating a total number of stars of 193000 +-
19000. The shapes of the surface brightness and density-number profiles versus
the radial coordinate r (instead of the projected coordinate R) lead to a
decreasing luminosity for an average star, and thus of mass, up to 1 arcmin,
quantifying the mass segregation. The deprojected model does not show evidence
of mass segregation outside this region
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