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Ages and Metallicities of Extragalactic Globular Clusters from Spectral and Photometric Fits of Stellar Population Synthesis Models
Spectra of galaxies contain an enormous amount of information about therelative mixture of ages and metallicities of constituent stars. Wepresent a comprehensive study designed to extract the maximuminformation from spectra of data quality typical in large galaxysurveys. These techniques are not intended for detailed stellarpopulation studies that use high-quality spectra. We test techniques ona sample of globular clusters, which should consist of single stellarpopulations and provide good test cases, using the Bruzual-Charlothigh-resolution stellar population synthesis models to simultaneouslyestimate the ages and metallicities of 101 globular clusters in M31 andthe Magellanic Clouds. The clusters cover a wide range of ages andmetallicities, 4 Myr
| Results of the ESO-SEST Key Programme on CO in the Magellanic Clouds. X. CO emission from star formation regions in LMC and SMC
We present J=1-0 and J=2-1 12CO maps of several star-formingregions in both the Large and the Small Magellanic Cloud, and brieflydiscuss their structure. Many of the detected molecular clouds arerelatively isolated and quite small with dimensions of typically 20 pc.Some larger complexes have been detected, but in all cases the extent ofthe molecular clouds sampled by CO emission is significantly less thanthe extent of the ionized gas of the star-formation region. Very littlediffuse extended CO emission was seen; diffuse CO in between orsurrounding the detected discrete clouds is either very weak or absent.The majority of all LMC lines of sight detected in 13CO hasan isotopic emission ratio I( 12CO)/I( 13CO) ofabout 10, i.e. twice higher than found in Galactic star-formingcomplexes. At the lowest 12CO intensities, the spread ofisotopic emission ratios rapidly increases, low ratios representingrelatively dense and cold molecular gas and high ratios marking COphoto-dissociation at cloud edges.
| 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.
| Kinematics of the very young nebula N59 at the edge of the supershell LMC4
The dynamics of the nebula N59 (B053540-6736), located at the boundaryof the supershell LMC4 in the Large Magellanic Cloud, is studied using ascanning Fabry-Perot interferometer. It is shown that the nebulae NGC2032 and 2035, which form the bright core of the H II region N59A(B053530-6736), belong to a single H II region which looks divided dueto the presence of a heavy dust lane. This bright core presents anexpansion motion of 24 km s(-1) . The kinetic energy involved in thismotion is of about 1.5 x 10(49) erg. This value is compatible eitherwith a supernova explosion origin or with a formation by the winds ofinterior massive stars. Since no clear traces of a SN explosion havebeen found in this nebula and since the stellar content of N59A(B053530-6736) is rich in blue stars, we conclude that these stars,mainly the very massive star HDE 269810 (R122), and probably other starshidden by the dust lane, are sufficient in providing the wind power todrive the expansion motion. The dust lane seems to be mixed in with thenebular gas and the stars, suggesting a site where star formation maystill take place. An extended shell, probably ionized by the star R122,has been detected at the same velocities as the slab, at blueshiftedvelocity, seen in the foreground absorption. The star R122 contributesto the high excitation of the faint diffuse gas, and perhaps of somefarther nebulae. To the East, the SNR 0536-676 remains as a trace of theexistence of another massive star which had already exploded. Thekinematics of N59B (B053610-6736) which contains the SNR 0536-676, isalso studied, corroborating the results of previous studies. Based onobservations collected at the European Southern Observatory
| 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.
| Blue-violet spectral evolution of young Magellanic Cloud clusters
We study the integrated spectral evolution in the blue-violet range of97 blue star clusters in the Magellanic Clouds, from those associatedwith gas emission to those as old as a few hundred Myr. Some clustersare dominated by the flux of those massive stars that pass throughevolutionary stages such as Wolf-Rayet, Luminous Blue Variable, Be, andsupergiant stars of different temperatures. The relationships amongspectral features such as absorption and emission lines, Balmerdiscontinuity and Balmer continuum are used to study the spectralevolution of the clusters. Finally, we sort into groups spectra ofsimilar evolutionary stages, creating a template spectral library withpossible applications in stellar populations syntheses of star-forminggalaxies and in the spectral simulation of bursts of star formation withdifferent mean ages and durations.
| The stellar content of the Large Magellanic Cloud II region N 59 A
We present UBV photometry of the stellar cluster associated with N59A, adusty H II region in the LMC. N59A's main detected source of ionizationis an O5V (or possibly earlier type) star with a visual extinction of1.2 mag. N59A also contains fifteen O-B3 stars that may contribute tothe ionization; these stars are affected by greatly differing amounts ofextinction. However, the observed stellar content of N59A cannotcompletely account for the ionization of the gas and the heating of theassociated dust. Some early massive star(s) still probably lieundetected in the core of (or behind) the central absorbing cloud. Inaddition to this young population associated with the H II region, wedetect an underlying older population of giant stars. We have alsodetected one Galactic star, and a few supergiant candidates. Theseresults are discussed in terms of the initial mass function.
| UBVRI aperture photometry of early-type galaxies
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1988A&AS...72..215P&db_key=AST
| Age determination of extragalactic H II regions
The H II region evolution models of Copetti et al. (1984) were comparedwith observational data of H II regions in the Magellanic Clouds, M 33,M 101 and of 'isolated extragalactic H II regions'. IMF with chi = 3 or2.5 are inconsistent with a large number of H II regions. The moreuniform age distribution of isolated extragalactic H II regions obtainedthrough an IMF with chi = 2 suggests that this value is more realisticthan chi = 1 or 1.5. The H II region age estimates indicate a burst ofstar formation about 5.5 + or - 1.0 10 to the -6th yr ago in the LMC andabout 2.3 + or - 0.9 x 10 to the 6th yr ago in the SMC. The observedforbidden O III/H-beta gradient in M 33 and M 101 must be caused bycolor temperature variation of the radiation ionizing the H II regions.
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