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|Blue and yellow long-period variables in the direction of the Small Magellanic Cloud|
Aims.We investigate the nature of a sample of 17 long-term periodicvariables in the direction of the Small Magellanic Cloud. Methods:.Based on new spectroscopic data, we determined spectral types, radialvelocities, absolute magnitudes, and colors for these stars. We presenta refined discussion of their OGLE light curves along with an analysisof their 2MASS photometry. Results: .Most stars turned out to beB-A giants members of the Small Magellanic Cloud. We find a newinteracting eclipsing binary with a period of 184 days and two newearly-type ellipsoidal variables. One of our objects is the ROSAT sourceRX J0058.2-7231. We analyzed 11-years of data forthis Be X-ray binary finding that their photometric period varies by ~4%quasiperiodically, on a time scale of ~1200 days. We find evidence ofmultiple photometric periods in 2 Ae-type and 1 late-Be type stars. Thecase of OGLE00445466-7328029 is especiallyinteresting, as this late-type Be star shows a beating phenomenonprimarily caused by two closely-spaced frequencies, 0.05733 c/d (17.44d) and 0.06347 c/d (15.76 d). Four other emission-line objects showstable long-term periodicities and probably correspond to Be-starbinaries. Transient photometric periods are only found in 4 non-emissionearly-type stars.
|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.
|Dating star clusters in the Small Magellanic Cloud by means of integrated spectra|
In this study flux-calibrated integrated spectra in the range(3600-6800) Å are presented for 16 concentrated star clusters inthe Small Magellanic Cloud (SMC), approximately half of which constituteunstudied objects. We have estimated ages and foreground interstellarreddening values from the comparison of the line strengths and continuumdistribution of the cluster spectra with those of template clusterspectra with known parameters. Most of the sample clusters are youngblue clusters (6-50 Myr), while L 28, NGC 643 and L 114 are found to beintermediate-age clusters (1-6 Gyr). One well known SMC cluster (NGC416) was observed for comparison purposes. The sample includes clustersin the surroundings and main body of the SMC, and the derived foregroundreddening values are in the range 0.00 <= E(B-V) <= 0.15. Thepresent data also make up a cluster spectral library at SMC metallicity.Based on observations made at Complejo Astronómico El Leoncito,which is operated under agreement between the Consejo Nacional deInvestigaciones Científicas y Técnicas de laRepública Argentina and the National Universities of La Plata,Córdoba and San Juan, Argentina.
|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. Multiple Cluster Candidates in the Small Magellanic Cloud|
We present the list of potential multiple star clusters from the centralpart of the SMC. Presented systems were selected from the catalog ofstar clusters from the SMC. We find 23 suspected cluster pairs and 4triple systems. The statistical analysis suggests that many of them mayconstitute physical systems. Size, equatorial coordinates and age ofpresented clusters are given. Age of clusters which form five pairs andone triple system is coeval suggesting common origin of these objects.
|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.
|The Optical Gravitational Lensing Experiment. Variable Stars in Star Clusters of the Magellanic Clouds. I.Eclipsing Systems in the Clusters of the SMC|
The list of 127 eclipsing stars in optical coincidence with starclusters from the SMC is presented. It was prepared using the catalogsof eclipsing systems and star clusters from the SMC based onobservations collected during the OGLE-II microlensing project. Locationof 12 eclipsing stars in the color-magnitude diagram of clusters allowsto exclude their membership. Photometric data of 73 systems supporttheir membership. The remaining 42 objects were found in loose, faintclusters and therefore no conclusive statement about their membershipcan be made. All presented data are available from the OGLE archive.
|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.
|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.
|A New Catalogue of Hα Emission Line Stars and Small Nebulae in the Small Magellanic Cloud|
An objective-prism survey of the Small Magellanic Cloud has beenperformed through an Hα + [N II] interference filter, using the0.90 m Curtis Schmidt telescope of Cerro Tololo. 1898 emission-lineobjects have been detected in the main body of this galaxy, almostquadrupling the number of those found, in the same region, by theprevious objective-prism surveys. Among these objects are newlydiscovered planetary nebulae, compact HII regions and late-type stars.Continuum intensity, as well as the shape and relative strength of theHα emission-line have been estimated; coordinates, cross-identifications for the listed objects and 2.25 arcmin square findingcharts for all the objects are provided.
|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.
|The morphology of star clusters in the SMC|
The projected ellipticities of 34 populous SMC star clusters have beenderived by means of PDS 1010A scans and a computer interactive method ofreduction implemented on an Apollo 570 workstation. A pair of J and Rplates taken with the 1.2 m UK Schmidt telescope in Australia were used.Radial ellipticity variations within individual globular clusters seemto be a common phenomenon for the SMC clusters, similar to that observedin the LMC clusters where the innerparts are more elliptical than theouter ones in 95 percent of the cases. The derived ellipticities whichcorrespond to the innermost part of the cluster at radial distances nearto half-mass radii have been found to be statistically more ellipticalthan those of the LMC, known to be more elliptical than those of theGalaxy. The dynamical masses of the clusters seem to correlate withellipticities supporting the hypothesis that, either the gravitationalfield of the parent galaxy being a dominant factor affect slower theshape of the high mass clusters and/or the most massive clusters, beingdynamically younger, retain their original shape.
|Cluster pairs in the Small Magellanic Cloud|
The cluster system of the SMC has been surveyed with the aim ofidentifying close pairs of clusters. It is found that the number ofexisting close cluster pairs is significantly (at the 3.5 sigma level)larger than the expected number of such pairs due to the chance line-upof single clusters, implying that some of these pairs are physicallyassociated. Comparison with the LMC cluster system shows that the ratioof pairs is similar to the ratio of single clusters in the two galaxies.These results, combined with the earlier results for the LMC, indicatethe tendency of clusters to form in pairs, or possibly in groups, atleast in the case of irregular galaxies, the probability that theobserved number of pairs having formed due to tidal capture being small.
|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.|
|A new catalogue of emission-line stars and planetary nebulae in the Small Magellanic Cloud|
Abstract image available at:http://adsabs.harvard.edu/abs/1961AJ.....66..169L
|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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