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|Age distribution of young clusters and field stars in the Small Magellanic Cloud|
Aims.In this paper we discuss the cluster and field star formation inthe central part of the Small Magellanic Cloud. The main goal is tostudy the correlation between young objects and their interstellarenvironment. Methods: . The ages of about 164 associations and 311clusters younger than 1 Gyr are determined using isochrone fitting. Thespatial distribution of the clusters is compared with the HI maps, withthe HI velocity dispersion field, with the location of the CO clouds andwith the distribution of young field stars. Results: .The clusterage distribution supports the idea that clusters formed in the last 1Gyr of the SMC history in a roughly continuous way with periods ofenhancements. The two super-shells 37A and 304A detected in the HIdistribution are clearly visible in the age distribution of theclusters: an enhancement in the cluster formation rate has taken placefrom the epoch of the shell formation. A tight correlation between youngclusters and the HI intensity is found. The degree of correlation isdecreasing with the age of the clusters. Clusters older than 300 Myr arelocated away from the HI peaks. Clusters and associations younger than10 Myr are related to the CO clouds in the SW region of the SMC disk. Apositive correlation between the location of the young clusters and thevelocity dispersion field of the atomic gas is derived only for theshell 304A, suggesting that the cloud-cloud collision is probably notthe most important mechanism of cluster formation. Evidence ofgravitational triggered episode due to the most recent close interactionbetween SMC and LMC is found both in the cluster andfield star distribution.
|The Star Clusters of the Small Magellanic Cloud: Age Distribution|
We present age measurements for 195 star clusters in the SmallMagellanic Cloud based on comparison of integrated colors measured fromthe Magellanic Clouds Photometric Survey with models of simple stellarpopulations. We find that the modeled nonuniform changes of clustercolors with age can lead to spurious age peaks in the cluster agedistribution; that the observed numbers of clusters with age t declinessmoothly as t-2.1 that for an assumed initial cluster massfunction scaling as M-2, the dependence of the clusterdisruption time on mass is proportional to M0.48; thatdespite the apparent abundance of young clusters, the dominant epoch ofcluster formation was the initial one; and that there are significantdifferences in the spatial distribution of clusters of different ages.Because of limited precision in our age measurements, we cannot addressthe question of detailed correspondence between the cluster age functionand the field star formation history. However, this sample provides aninitial guide as to which clusters to target in more detailed studies ofspecific age intervals.
|Infrared Surface Brightness Fluctuations of Magellanic Star Clusters|
We present surface brightness fluctuations (SBFs) in the near-IR for 191Magellanic star clusters available in the Second Incremental and All SkyData releases of the Two Micron All Sky Survey (2MASS) and compare themwith SBFs of Fornax Cluster galaxies and with predictions from stellarpopulation models as well. We also construct color-magnitude diagrams(CMDs) for these clusters using the 2MASS Point Source Catalog (PSC).Our goals are twofold. The first is to provide an empirical calibrationof near-IR SBFs, given that existing stellar population synthesis modelsare particularly discrepant in the near-IR. Second, whereas mostprevious SBF studies have focused on old, metal-rich populations, thisis the first application to a system with such a wide range of ages(~106 to more than 1010 yr, i.e., 4 orders ofmagnitude), at the same time that the clusters have a very narrow rangeof metallicities (Z~0.0006-0.01, i.e., 1 order of magnitude only). Sincestellar population synthesis models predict a more complex sensitivityof SBFs to metallicity and age in the near-IR than in the optical, thisanalysis offers a unique way of disentangling the effects of age andmetallicity. We find a satisfactory agreement between models and data.We also confirm that near-IR fluctuations and fluctuation colors aremostly driven by age in the Magellanic cluster populations and that inthis respect they constitute a sequence in which the Fornax Clustergalaxies fit adequately. Fluctuations are powered by red supergiantswith high-mass precursors in young populations and by intermediate-massstars populating the asymptotic giant branch in intermediate-agepopulations. For old populations, the trend with age of both fluctuationmagnitudes and colors can be explained straightforwardly by evolution inthe structure and morphology of the red giant branch. Moreover,fluctuation colors display a tendency to redden with age that can befitted by a straight line. For the star clusters only,(H-Ks)=(0.21+/-0.03)log(age)-(1.29+/-0.22) once galaxies areincluded, (H-Ks)=(0.20+/-0.02)log(age)-(1.25+/-0.16).Finally, we use for the first time a Poissonian approach to establishthe error bars of fluctuation measurements, instead of the customaryMonte Carlo simulations.This research has made use of the NASA/ IPAC Infrared Science Archive,which is operated by the Jet Propulsion Laboratory, California Instituteof Technology, under contract with the National Aeronautics and SpaceAdministration.
|Magellanic Clouds stellar clusters. II. New B,V CM diagrams for 6 LMC and 10 SMC clusters|
We present new CCD photometry for 6 LMC and 10 SMC stellar clusterstaken at the ESO 1.54-m Danish Telescope in La Silla, to extend aprevious investigation on Magellanic Clouds clusters based on HSTsnapshots. Thanks to the much larger area covered by the Danishdetector, we investigate the spatial distribution of cluster stars,giving V, (B-V) CM diagrams for both clusters and surrounding fields.Evidence of a complex history of star formation in the Clouds isoutlined, showing that old field populations in both Clouds havemetallicities much lower than normally adopted for them (Z = 0.008 and Z= 0.004 for LMC and SMC respectively), with SMC field stars more metalpoor than in the LMC. Observational data concerning the red clump offield stars in both Clouds are briefly discussed. Based on observationscarried out at the European Southern Observatory, La Silla, Chile.
|Morphologies and ages of star cluster pairs and multiplets in the Small Magellanic Cloud|
An isophotal atlas of 75 star cluster pairs and multiplets in the SmallMagellanic Cloud is presented, comprising 176 objects. They areconcentrated in the SMC main body. The isophotal contours were made fromDigitized Sky Survey* images and showed relevant structuralfeatures possibly related to interactions in about 25% of the sample.Previous N-body simulations indicate that such shapes could be due totidal tails, bridges or common envelopes. The diameter ratio between themembers of a pair is preferentially in the range 1 - 2, with a peak at1. The projected separation is in the range ~ 3 - 22 pc with apronounced peak at ~ 13 pc. For 91 objects it was possible to deriveages from Colour-Magnitude Diagrams using the OGLE-II photometricsurvey. The cluster multiplets in general occur in OB stellarassociations and/or HII region complexes. This indicates a common originand suggests that multiplets coalesce into pairs or single clusters in ashort time scale. Pairs in the SMC appear to be mostly coeval andconsequently captures are a rare phenomenon. We find evidence that starcluster pairs and multiplets may have had an important role in thedynamical history of clusters presently seen as large single objects.The images in this study are based on photographic data obtained usingthe UK Schmidt Telescope, which was operated by the Royal ObservatoryEdinburgh, with funding from the UK Science and Engineering ResearchCouncil, until 1988 June, and thereafter by the Anglo-AustralianObservatory. Original plate material is copyright by the RoyalObservatory Edinburgh and the Anglo-Australian Observatory. The plateswere processed into the present compressed digital form with theirpermission. The Digitized Sky Survey was produced at the Space TelescopeScience Institute under US Government grant NAG W-2166.
|Updating the Census of Star Clusters in the Small Magellanic Cloud|
Surveys using CCD detectors are retrieving bright and faint catalogedclusters and revealing new ones in the Magellanic Clouds. This paperdiscusses the contribution of the OGLE Survey to the overall census ofstar clusters in the Small Magellanic Cloud (SMC). A detailedcross-identification indicates that the new objects in the SMC OGLEcatalog are 46. The increase in the number of cataloged clusters is ~7%,the total sample being ~700. This updated census includes embeddedclusters in H II regions and a density range attaining loose systems.
|The Optical Gravitational Lensing Experiment. Cepheids in Star Clusters from the Magellanic Clouds|
We present Cepheids located in the close neighborhood of star clustersfrom the Magellanic Clouds. 204 and 132 such stars were found in the LMCand SMC, respectively. The lists of objects were constructed based oncatalogs of Cepheids and star clusters, recently published by theOGLE-II collaboration. Location of selected Cepheids on the skyindicates that many of them are very likely cluster members. Photometricdata of Cepheids and clusters are available from the OGLE Internetarchive.
|The Optical Gravitational Lensing Experiment. Age of Star Clusters from the SMC|
We present determination of age of clusters from 2.4 square degreeregion of the SMC bar. The photometric data were taken from the BVI mapsof the SMC and catalog of clusters in this galaxy obtained during theOGLE-II microlensing survey. For 93 well populated SMC clusters theirage is derived with the standard procedure of isochrone fitting. Thedistribution of age of cluster from the SMC is presented. It indicateseither non-uniform process of cluster formation or very effectivedisruption of clusters.
|Optical Gravitational Lensing Experiment. The Catalog of Clusters in the Small Magellanic Cloud|
We present the catalog of clusters found in the area of approx 2.4square degree in the central regions of the Small Magellanic Cloud. Thecatalog contains data for 238 clusters, 72 of them are new objects. Foreach cluster equatorial coordinates, radii, approximate number ofmembers, cross-identification, finding chart and color magnitudediagrams: V-(B-V) and V-(V-I) are provided. Photometric data for allclusters presented in the catalog are available from the OGLE Internetarchive.
|Cepheids in MC Clusters: New Observations|
|A Revised and Extended Catalog of Magellanic System Clusters, Associations, and Emission Nebulae. I. Small Magellanic Cloud and Bridge|
A survey of extended objects in the Magellanic System was carried out onthe ESO/SERC R and J Sky Survey Atlases. The present work is dedicatedto the Small Magellanic Cloud and to the inter-Magellanic Cloud region("Bridge") totaling 1188 objects, of which 554 are classified as starclusters, 343 are emissionless associations, and 291 are related toemission nebulae. The survey includes cross-identifications amongcatalogs, and we present 284 new objects. We provide accurate positions,classification, homogeneous sizes, and position angles, as well asinformation on cluster pairs and hierarchical relation for superimposedobjects. Two clumps of extended objects in the Bridge and one at theSmall Magellanic Cloud wing tip might be currently forming dwarfspheroidal galaxies.
|Accurate positions for SMC clusters|
Positions of 203 SMC clusters accurate to + or - 5 arcsec are reported.The astrometry method used is briefly described. Plans for futureMagellanic Cloud cluster astrometry are summarized.
|A preliminary survey of collapsed cores in the Magellanic Clouds' globular clusters|
A preliminary report on a surface photometry survey for collapsed coresin the Magellanic Clouds' globular clusters is presented. Coremorphology classifications are given for the 33 globular clustersexamined so far. One cluster, NGC 2019, shows definite signs of acollapsed core, and two others, NGC 1774 and NGC 1951, appear as strongcandidates. This detection of postcollapse cores outside the Milky Wayopens some interesting prospects for future dynamical studies. However,the fraction of collapsed-core clusters appears to be smaller in theMagellanic Clouds than in the Galaxy. This may be due in part to theiryounger ages, or to the limitations imposed by the seeing effects. It isalso possible that the relative scarcity reflects the physicaldifference in the tidal field environments between the Galaxy and theClouds, in agreement with a trend found earlier, viz., that the tidalshocks from disk passages accelerate dynamical evolution and enhance thepropensity for core collapse.
|Observed radii and structural parameters of star clusters in the SMC. III|
The tidal radii, concentration parameters, and masses of 24 starclusters in the SMC have been derived by means of star counts. In thisinvestigation the seven most distant clusters (with projected distancesfrom the rotation center similar to the halo radius) are included aswell, and their masses are found to be about one hundred times lowerthan those of the halo clusters of the Galaxy.
|Age calibration and age distribution for rich star clusters in the Large Magellanic Cloud|
An empirical relation is presented for estimating the ages of rich starclusters in the Large Magellanic Cloud (LMC), to within a factor ofabout 2, from their integrated UBV colors. The calibration is based onpublished ages for 58 LMC clusters derived from main-sequencephotometry, integrated spectra, or the extent of the asymptotic giantbranches. Using stellar population models, a sample of LMC clusters moremassive than about 10,000 solar masses is isolated, which is correctedfor incompleteness as a function of magnitude. An unbiased agedistribution for three clusters is then determined. The number ofclusters decreases with increasing age in a manner that is qualitativelysimilar to the age distribution for the open clusters in our Galaxy. TheLMC age distribution is, however, flatter, and the median age of theclusters is greater. If the formation rate has been approximatelyconstant over the history of the two galaxies, then the age distributionobtained here implies that clusters are disrupted more slowly in theLMC. The results contain no evidence for bursts in the formation ofclusters, although fluctuations on small time scales and slow variationsover the lifetime of the LMC cannot be ruled out.
|Integrated magnitudes and colors of clusters in the magellanic clouds and Fornax system|
Data from PV, six-color, and four-color photometric observations ofclusters (38 in the Small Magellanic Cloud, 16 in the Large MagellanicCloud, four in the Fornax system, and NGC 1841) are reported. Theobservations were made in 1951, 1960-1961, 1959-1966, and 1974-1975using various telescopes and photometer setups at Mount StromloObservatory in Australia. Tables of integrated magnitudes and colors(both as originally observed and as reduced to the BV system) arepresented, and comparable published data are shown. The combined V dataare fitted to the theoretical luminosity profiles of King (1966) toestimate the total magnitudes and surface brightness distributions of 33of the clusters. Several sample profile fits are shown. A color-colorplot (V-B vs. G-R) is discussed in terms of identification of clustertypes by color: it is found that globular clusters can be separated fromother types, if all have the same amount of reddening.
|Photometric studies of composite stellar systems. V - Infrared photometry of star clusters in the Magellanic clouds|
Abstract image available at:http://adsabs.harvard.edu/abs/1983ApJ...266..105P
|UBV photometry for star clusters in the Small Magellanic Cloud.|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1978A&AS...34..431A&db_key=AST
|NGC and IC Objects in S. M. C.|
|Magnitudes of Clusters in the Small Magellanic Cloud|
|The cluster system of the Small Magellanic Cloud|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1958MNRAS.118..172L&db_key=AST
|Star Clusters in the Small Magellanic Cloud: I. Identification of 69 Clusters|
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