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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.
| 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.
| The Identifications of HDE Objects with Large Magellanic Cloud Clusters and Nebulae
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| A Catalogue of Clusters in The LMC
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