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|Spectral evolution of star clusters in the Large Magellanic Cloud. I. Blue concentrated clusters in the age range 40-300 Myr|
Aims.Integrated spectroscopy of a sample of 17 blue concentrated LargeMagellanic Cloud (LMC) clusters is presented and its spectral evolutionstudied. The spectra span the range ≈(3600-6800) Å with aresolution of ≈14 Å FWHM, being used to determine cluster agesand, in connection with their spatial distribution, to explore the LMCstructure and cluster formation history. Methods.Cluster reddeningvalues were estimated by interpolation, using the available extinctionmaps. We used two methods to derive cluster ages: (i) template matching,in which line strengths and continuum distribution of the clusterspectra were compared and matched to those of template clusters withknown astrophysical properties, and (ii) equivalent width (EW) method,in which new age/metallicity calibrations were used together withdiagnostic diagrams involving the sum of EWs of selected spectral lines(K Ca II, G band (CH), Mg I, Hδ, Hγ and Hβ).Results.The derived cluster ages range from 40 Myr (NGC 2130and SL 237) to 300 Myr (NGC 1932and SL 709), a good agreement between the results ofthe two methods being obtained. Combining the present sample withadditional ones indicates that cluster deprojected distances from theLMC center are related to age in the sense that inner clusters tend tobe younger. Conclusions.Spectral libraries of star clusters are usefuldatasets for spectral classifications and extraction of parameterinformation for target star clusters and galaxies. The present clustersample complements previous ones, in an effort to gather a spectrallibrary with several clusters per age bin.
|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.
|UBV photometry of Galactic foreground and LMC member stars - III. LMC member stars - a new data base|
New UBV photometry for 878 luminous member stars of the Large MagellanicCloud (LMC) and 13 stars of uncertain membership is presented. The datawill be available at Centre de Données astronomiques deStrasbourg. Including former observations now UBV data are available foraltogether 2470 luminous LMC stars and 2106 foreground stars plus 65stars of uncertain membership. The observations have been used alreadyfor several investigations dealing e.g. with interstellar reddeninglines and intrinsic colours, the dust distribution and the calibrationof charge-coupled device exposures.
|The Supergiant Shell LMC 2. I. The Kinematics and Physical Structure|
LMC 2 has the brightest, most coherent filamentary structure of allknown supergiant shells in the Large Magellanic Cloud. The opticalemission-line images show active star formation regions along thewestern edge and long filaments to the east. ROSAT PSPC and HRI imagesshow bright X-ray emission from within the shell boundary, indicatingthe presence of hot gas. Counterintuitively, neither high-resolutionechelle spectra in the Hα line nor aperture synthesis H I 21 cmemission-line observations show LMC 2 to have the kinematics expected ofan expanding shell. Rather, LMC 2 appears to consist of hot gas confinedbetween H I sheets. The interior surfaces of these sheets are ionized bythe UV flux of massive stars in the star formation regions along theperiphery of LMC 2, while the heating is provided by outflows of hot gasfrom the star formation regions and by SNRs interior to LMC 2. We havecompared LMC 2 to other supergiant shells in the LMC and in more distantgalaxies. When the spatial resolution of our data are degraded, we findthat LMC 2 resembles supergiant shells observed at a distance of 4 Mpcthat have previously been interpreted as expanding shells. Therefore,great caution should be exercised in the analysis and interpretation ofthe kinematics of distant supergiant shells to prevent overestimates oftheir velocities and total kinetic energies.
|A Revised and Extended Catalog of Magellanic System Clusters, Associations, and Emission Nebulae. II. The Large Magellanic Cloud|
A survey of extended objects in the Large Magellanic Cloud was carriedout on the ESO/SERC R and J Sky Survey Atlases, checking entries inprevious catalogs and searching for new objects. The census provided6659 objects including star clusters, emission-free associations, andobjects related to emission nebulae. Each of these classes containsthree subclasses with intermediate properties, which are used to infertotal populations. The survey includes cross identifications amongcatalogs, and we present 3246 new objects. We provide accuratepositions, classification, and homogeneous measurements of sizes andposition angles, as well as information on cluster pairs andhierarchical relation for superimposed objects. This unification andenlargement of catalogs is important for future searches of fainter andsmaller new objects. We discuss the angular and size distributions ofthe objects of the different classes. The angular distributions show twooff-centered systems with different inclinations, suggesting that theLMC disk is warped. The present catalog together with its previouscounterpart for the SMC and the inter-Cloud region provide a totalpopulation of 7847 extended objects in the Magellanic System. Theangular distribution of the ensemble reveals important clues on theinteraction between the LMC and SMC.
|Integrated UBV Photometry of 624 Star Clusters and Associations in the Large Magellanic Cloud|
We present a catalog of integrated UBV photometry of 504 star clustersand 120 stellar associations in the LMC, part of them still embedded inemitting gas. We study age groups in terms of equivalent SWB typesderived from the (U-B) X (B-V) diagram. The size of the spatialdistributions increases steadily with age (SWB types), whereas adifference of axial ratio exists between the groups younger than 30 Myrand those older, which implies a nearly face-on orientation for theformer and a tilt of ~45^deg^ for the latter groups. Asymmetries arepresent in the spatial distributions, which, together with thenoncoincidence of the centroids for different age groups, suggest thatthe LMC disk was severely perturbed in the past.
|The cluster system of the Large Magellanic Cloud|
A new catalog of clusters in the Large Magellanic Cloud has beenconstructed from searches of the IIIa-J component of the ESO/SERCSouthern Sky Atlas. The catalog contains coordinate and diametermeasurements of 1762 clusters in a 25 deg x 25 deg area of sky centeredon the LMC, but excluding the very crowded 3.5 sq deg region around theBar. The distribution of these clusters appears as two superimposedelliptical systems. The higher density inner system extends over about 8deg; the lower density outer system can be represented by a 13 deg x 10deg disk inclined at 42 deg to the line of sight. There are suggestionsof two weak 'arms' in the latter.
|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.
|The Identifications of HDE Objects with Large Magellanic Cloud Clusters and Nebulae|
|Identification of stars in the direction of the Large Magellanic Cloud - Second series|
A set of 52 charts published by Hodge and Wright (1967) is used toidentify both stars of the Large Magellanic Cloud (LMC) and galacticstars in the direction of the LMC. The stars identified are listed inthe Fehrenbach and Duflot catalogues of 1970, 1973, and 1981.
|Radial velocities from objective-prism plates in the direction of the Large Magellanic Cloud. List of 398 stars, LMC members. List of 1434 galactic stars, in the LMC direction|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1974A&AS...13..173F&db_key=AST
|Large Magellanic Cloud. 2nd list of L. M. C. members and list of galactic stars|
Abstract image available at:http://adsabs.harvard.edu/abs/1973A&AS...10..231F
|Grand Nuage de Magellan. Liste des etoiles membres DU Grand Nuage de Magellan et liste d'etoiles galactiques|
|A Catalogue of Clusters in The LMC|
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