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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
| Classification of Spectra from the Infrared Space Observatory PHT-S Database
We have classified over 1500 infrared spectra obtained with the PHT-Sspectrometer aboard the Infrared Space Observatory according to thesystem developed for the Short Wavelength Spectrometer (SWS) spectra byKraemer et al. The majority of these spectra contribute to subclassesthat are either underrepresented in the SWS spectral database or containsources that are too faint, such as M dwarfs, to have been observed byeither the SWS or the Infrared Astronomical Satellite Low ResolutionSpectrometer. There is strong overall agreement about the chemistry ofobjects observed with both instruments. Discrepancies can usually betraced to the different wavelength ranges and sensitivities of theinstruments. Finally, a large subset of the observations (~=250 spectra)exhibit a featureless, red continuum that is consistent with emissionfrom zodiacal dust and suggest directions for further analysis of thisserendipitous measurement of the zodiacal background.Based on observations with the Infrared Space Observatory (ISO), aEuropean Space Agency (ESA) project with instruments funded by ESAMember States (especially the Principle Investigator countries: France,Germany, Netherlands, and United Kingdom) and with the participation ofthe Institute of Space and Astronautical Science (ISAS) and the NationalAeronautics and Space Administration (NASA).
| A statistical study of binary and multiple clusters in the LMC
Based on the Bica et al. (\cite{bica}) catalogue, we studied the starcluster system of the LMC and provide a new catalogue of all binary andmultiple cluster candidates found. As a selection criterion we used amaximum separation of 1farcm4 corresponding to 20 pc (assuming adistance modulus of 18.5 mag). We performed Monte Carlo simulations andproduced artificial cluster distributions that we compared with the realone in order to check how many of the found cluster pairs and groups canbe expected statistically due to chance superposition on the plane ofthe sky. We found that, depending on the cluster density, between 56%(bar region) and 12% (outer LMC) of the detected pairs can be explainedstatistically. We studied in detail the properties of the multiplecluster candidates. The binary cluster candidates seem to show atendency to form with components of similar size. When possible, westudied the age structure of the cluster groups and found that themultiple clusters are predominantly young with only a few cluster groupsolder than 300 Myr. The spatial distribution of the cluster pairs andgroups coincides with the distribution of clusters in general; however,old groups or groups with large internal age differences are mainlylocated in the densely populated bar region. Thus, they can easily beexplained as chance superpositions. Our findings show that a formationscenario through tidal capture is not only unlikely due to the lowprobability of close encounters of star clusters, and thus the evenlower probability of tidal capture, but the few groups with largeinternal age differences can easily be explained with projectioneffects. We favour a formation scenario as suggested by Fujimoto &Kumai (\cite{fk}) in which the components of a binary cluster formedtogether and thus should be coeval or have small age differencescompatible with cluster formation time scales. Table 6 is only availablein electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/391/547
| A CO Survey of the LMC with NANTEN: III. Formation of Stellar Clusters and Evolution of Molecular Clouds
In order to elucidate star formation in the LMC, we made a completestudy of CO clouds with NANTEN. In the present paper, we compare 55giant molecular clouds (GMCs), whose physical quantities were welldetermined, with young objects, such as young stellar clusters and HIIregions. We find that the GMCs are actively forming stars and clusters;23 and 40 are found to be associated with the clusters and the HIIregions, respectively. The clusters associated with the GMCs aresignificantly young; ~ 85% of them are younger than ~ 10 Myr. Inaddition, compact groups of the young clusters are often found at thepeak position of the GMCs, e.g., N 159 and N 44, while much loosergroups are away from the GMCs. This suggests that the clusters areformed in groups and disperse as they become old. The distributions ofthe CO, [CII], and UV indicate that the GMCs are likely to be rapidlydissipated within several Myr due to UV photons from the clusters. Wealso estimate the evolutionary time scale of the GMCs; they form starsin a few Myr after their birth, and form clusters during the next fewMyr, and are dissipated in the subsequent few Myr.
| 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.
| Star Clusters Driven to Form by Strong Collisions Between Gas Clouds in High-Velocity Random Motion
Abstract image available at:http://adsabs.harvard.edu/abs/1997AJ....113..249F
| Molecular abundances in the Magellanic Clouds. I. A multiline study of five cloud cores.
Nine Hii regions of the LMC were mapped in ^13^CO(1-0) and three in^12^CO(1-0) to study the physical properties of the interstellar mediumin the Magellanic Clouds. For N113 the molecular core is found to have apeak position which differs from that of the associated Hii region by20". Toward this molecular core the ^12^CO and ^13^CO peak T_MB_ linetemperatures of 7.3K and 1.2K are the highest so far found in theMagellanic Clouds. The molecular concentrations associated with N113,N44BC, N159HW, and N214DE in the LMC and LIRS36 in the SMC wereinvestigated in a variety of molecular species to study the chemicalproperties of the interstellar medium. I(HCO^+^)/I(HCN) andI(HCN)/I(HNC) intensity ratios as well as lower limits to theI(^13^CO)/I(C^18^O) ratio were derived for the rotational 1-0transitions. Generally, HCO^+^ is stronger than HCN, and HCN is strongerthan HNC. The high relative HCO^+^ intensities are consistent with ahigh ionization flux from supernovae remnants and young stars, possiblycoupled with a large extent of the HCO^+^ emission region. The bulk ofthe HCN arises from relatively compact dense cloud cores. Warm orshocked gas enhances HCN relative to HNC. From chemical modelcalculations it is predicted that I(HCN)/I(HNC) close to one should beobtained with higher angular resolution (<~30") toward the cloudcores. Comparing virial masses with those obtained from the integratedCO intensity provides an H_2_ mass-to-CO luminosity conversion factor of1.8x10^20^mol/cm^2^(K.km/s)^-1^ for N113 and2.4x10^20^mol/cm^2^(K.km/s)^-1^ for N44BC. This is consistent withvalues derived for the Galactic disk.
| UBV Photometry of OB Associations within Superbubbles of the Large Magellanic Cloud
This work presents UBV photometry of the stellar populations associatedwith seven superbubble nebulae and five classical H II regions in theLarge Magellanic Cloud. Although the nebular morphology of thesuperbubbles appears to be substantially evolved compared to theclassical nebulae, the color-magnitude diagrams do not reveal anynoticeable correlation between the resident stellar population andnebular morphology. The photometry presented here will be used in aforthcoming paper to examine further the stellar content and dynamics ofthese superbubbles.
| 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.
| Starbursts in barred spiral galaxies. I. MKN 712, a new Wolf-Rayet galaxy.
We report the discovery of emission from Wolf-Rayet stars in a giant HIIregion 4.5 arcsec South of the nucleus of the IRAS barred spiral galaxyMkn 712 (= UGC 5342). The ratio of WNL to OV stars, estimated from theluminosity of the Heiiλ4686 line, is 0.2. By comparison withstarburst and stellar evolution models, we find that this high value isonly compatible with a very young starburst episode (3-4Myr) and a flatinitial mass function ({GAMMA}=-1). The presence of the [Ar V] linereveals that the HII region is strongly ionized by the hot Wolf-Rayetstars. The comparison with other barred Wolf-Rayet galaxies suggeststhat the detection of Wolf-Rayet stars depends on the dust content andorientation of the galaxy.
| 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.
| Ultraviolet spectral evolution of star clusters in the IUE library.
The ultraviolet integrated spectra of star clusters and H II regions inthe IUE library have been classified into groups based on their spectralappearance, as well as on age and metallicity information from otherstudies. We have coadded the spectra in these groups according to theirS/N ratio, creating a library of template spectra for futureapplications in population syntheses in galaxies. We define spectralwindows for equivalent width measurements and for continuum tracings.These measurements in the spectra of the templates are studied as afunction of age and metallicity. We indicate the windows with a strongmetallicity dependence, at different age stages.
| Extinction characteristics of giant HII regions - Star-forming complexes in the galaxies M33, LMC, and NGC 2403
The discrepancies between the extinction of gas emission and that of thestarlight in giant HII regions, star-forming complexes in the galaxiesM33, LMC, and NGC 2403, were empirically investigated. The extinctionvalues were determined for 30 stars in eight associations in M33. Anempirical relation between the extinction of starlight and that of thegas emission in giant HII regions, star-forming complexes in thegalaxies under study, was obtained.
| A radio continuum study of the Magellanic Clouds. IV. Catalogues of radio sources in the Large Magellanic Cloud at 1.40, 2.45, 4.75, 4.85 and 8.55 GHz.
From observations with the Parkes radio telescope, we present cataloguesof radio sources in the Large Magellanic Cloud at four frequencies:1.40, 2.45, 4.75 and 8.55GHz, and an additional catalogue from a sourceanalysis of the Parkes-MIT-NRAO survey at 4.85GHz. A total of 469sources have been detected at least one of these frequencies, 132 ofwhich are reported here for the first time as radio sources.
| An atlas of the interstellar environment of Wolf-Rayet stars in the Magellanic clouds
We have made a complete study of the interstellar environment around theWolf-Rayet stars in the Magellanic Clouds. We present, in the form of anatlas, the results of a complete imaging survey in Hα and of anextensive survey in the (O III) alpha 5007 emission line. As a result ofthis survey, we have more than doubled the total number of ring nebulaeknown. These include cases of both rings of stellar ejecta and ringnebulae resulting from the sweeping up of the surrounding interstellarmedium. We find that 34% of WN3-WN4 stars, 36% of late WN types, and 26%of WC4-WC5 stars are associated with a ring nebula of some kind. Thesefigures are very similar to the percentage of Wolf-Rayet stars havingring nebulae in the solar neighborhood. The size distribution of ringnebulae is also similar. From the fact that the majority of Wolf-Rayetstars do not show ring nebulae, it is clear that mass loss in earlierphases of evolution, and the collective effects of the energy input fromthe clusters of OB stars with which the Wolf-Rayet stars are frequentlyassociated, has profoundly modified the preexisting circumstellarenvironment. However, on the basis of statistics, we cannot exclude thepossibility that all Wolf-Rayet stars have possessed a ring nebula atsome stage in their evolution.
| Results of the ESO / SEST Key Programme on Co/ in the Magellanic Clouds - Part One - a Survey of Co/ in the Large Magellanic Cloud and the Small Magellanic Cloud
As the first part of the ESO-Swedish SEST Key Programme on CO in theMagellanic Clouds, we have observed ^12^CO J = 1-0 towards 92 positionsin the LMC and 42 positions in the SMC. In the SMC we searched foremission from H II regions, dark clouds and IRAS infrared sources. Thegenerally negative detection rate of non-IRAS sources in the SMC led toan LMC source selection based on the IRAS results. In both galaxies, COwas detected towards the majority of sources observed. We also observed^13^C0 J = 1-0 towards the brighter ^12^CO sources in the LMC (37) andSMC (9). Compared to the strength of CO lines observed in the Milky WayGalaxy with identical linear resolutions, velocity-integrated COemission is weaker by at least a factor of three in the LMC sources andan order of magnitude in the SMC sources. The mean velocity-integratedisotopic intensity ratio I_12_/I_13_ is 12.5 in the LMC and about 15 inthe SMC. Individual ratios range from 8.5 to 20. These isotopicintensity ratios are two to three times higher than those found inGalactic molecular clouds.
| A catalogue of binary star cluster candidates in the Large Magellanic Cloud
A photographic atlas of close pairs of star clusters in the LargeMagellanic Cloud is presented here. The criterion for inclusion ofcluster pairs in the atlas was an upper limit of 18.7 pc for theprojected separation between the centers of the clusters in each pair.Accurate coordinates for the clusters, the projected separations andestimates of the diameters and positional angles are given and some ofthe global properties of the cluster-pair population of the LMC arediscussed. It is found that the individual clusters in pairspreferentially have nearly equal sizes.
| 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.
| Binary star clusters in the Large Magellanic Cloud
In a survey of the LMC cluster system, double clusters with acenter-to-center separation of less than 1.3 arcmin (18 pc) have beenidentified. It is inferred that a considerable fraction of these doubleclusters must be binaries since the calculated projection effects canaccount for only 31 of them. This inference is strongly supported by thefact that the ages available for some of the culsters of the sample (asdetermined from UBV photometry) are less than the computed times ofmerger or disruption of the binary cluster system. Furthermore, thespace distribution of these pairs indicates that these clusters belongto a very young or young population.
| Clarifications of Some Identifications for the LMC Region
Not Available
| First observations with the scanning Fabry-Perot interferometer CIGALE - The stellar wind bubble N 62 B in the Large Magellanic Cloud
The CIGALE instrument, specially adapted to low flux observations,establishes that the faint LMC nebula N 62 B (DEM 235) is asemispherical bubble, exhibiting few filaments, with dimensions of 45 x60 pc. The gaseous luminosities and kinematics are interrupted ascorresponding to an expansion motion around the O8I central star. Anexpanding velocity of + or - 35 km/s is obtained. The systemic velocity,determined from the shell edge-on, is 282 km/s, the rms precision of theindividual measures being 7.2 km/s. The first estimate of rms electrondensities gives values within the range of usual densities in bubbles(0.3 - 3/cu cm).
| 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.
| Observations of giant bubbles in the Large Magellanic Cloud
Forbidden line S II/H-alpha intensity line ratio mapping and radialvelocity data as well as monochromatic photographs are presented for asample of bubbles in the LMC and some classical H II regions. Thebubbles of unknown origin have line ratios greater than those of the HII regions and thus appear to fill the gap between thermal andnonthermal radio sources. All the bubbles or filamentary nebulae haveimportant internal kinematical motions while the velocity dispersion isabout 6-7 km/s for the H II regions. The large complex nebulae havevalues similar to simple H II regions in their brightest parts, whilethe faintest parts exhibit greater dispersions and conspicuoussplittings and broadenings. The ionized bubbles appear to beintermediate between classical young H II regions and supernovaremnants.
| The carbon abundance in the Magellanic Clouds from IUE observations of H II regions
Results are given of observations of the UV spectra of several H IIregions in the Magellanic Clouds, with emphasis on obtaining the carbonabundance from the UV lines of C II, C III, and C IV. The observationsand results are described, and theoretical model calculations arepresented of the H II regions and the relative abundances of H, He, C,N, O, S, Cl, and Ar computed from the UV and visual spectra. Inaddition, the abundance results for the Magellanic Clouds are comparedwith the sun, the Orion Nebula, and galactic planetary nebulae. Incomparison with solar abundances, carbon is found to be depletedrelative to hydrogen in the Magellanic Clouds by an amount larger thanthat of nitrogen and oxygen in the SMC and by an amount between that ofnitrogen and oxygen in the LMC. It is noted that the results areconsistent with a scenario that nitrogen and oxygen have greater primaryyields in massive stars than carbon, which may be produced predominantlyin less massive stars (such that C/N and C/O in galaxies are initiallyvery low and subsequently increase with evolution). Subsequently, theC/N ratio may decrease as secondary production of nitrogen in lessmassive stars becomes significant.
| More Wolf-Rayet stars in the Large Magellanic Cloud
Abstract image available at:http://adsabs.harvard.edu/abs/1980A&AS...39...19A
| A survey of chemical compositions of H II regions in the Magellanic Clouds
The reported investigation had the objective to extend abundancedeterminations to a larger number of H II regions in the Small Cloud(and a few more in the Large Cloud) in connection with a study regardingthe possible occurrence of large-scale abundance gradients analogous tothose found in Sc galaxies and in the Galaxy, taking into account alsoquestions concerning the existence of a characteristic abundance patternrepresenting the entire young population of either cloud. It is foundthat the laws governing enrichment of the interstellar medium are verysimilar in the Magellanic Clouds to what they are in the outer parts ofSc galaxies, including the very massive system M101. There is no reasonto believe that any special process such as preferential escape of gashas operated to reduce the effective yield in the Magellanic Clouds.
| The nebular complexes of the large and small Magellanic Clouds
Long exposures of the complexes of ionized hydrogen in both the LMC andSMC have been taken with the 48-in. SRC Schmidt camera through a H-alpha+ forbidden NII interference filter of 100-A bandwidth. These plates andidentifying charts are presented in a form in which little informationis lost. A catalog of many individual emission regions in both thesegalaxies is also compiled. The relationships between the nebulositiesand OB associations as well as between 21-cm neutral hydrogen emissionand continuum radio emission are discussed, and a number ofsupernova-remnant candidates are listed for further study.
| Chemical composition of H II regions in the Large Magellanic Cloud and its cosmological implications
Abstract image available at:http://adsabs.harvard.edu/abs/1974ApJ...193..327P
| A catalogue of stellar associations in the Large Magellanic Cloud.
Abstract image available at:http://adsabs.harvard.edu/abs/1970AJ.....75..171L
| Objects having peculiar spectra.
Not Available
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