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High spatial resolution radio continuum observations of compact H {II} regions in the Magellanic Clouds
We present high spatial resolution observations of the 6 cm continuumemission of compact H II regions in well-known sites of massive starformation located in the Small and Large Magellanic Clouds. Theobservations include N81 in the SMC, and N4A, N83B, N11A, N160A andN159-5 in the LMC. Some of the compact H II regions are isolated, whileothers are embedded in more diffuse ionised regions. A description ofthe radio morphology of the sources, together with comparisons withother observations, is given in detail. The regions cover a wide rangein size (from ˜ 0.1 to 7 pc), rms electron density (from ˜200 to 6500 cm-3), emission measure (from~3×105 to 2×107 pc cm-6),ionised gas mass (from ˜ 0.2 to 750 Mȯ) and rateof Lyman continuum photons (from ~ 3× 1047 to5×1049 s-1). The spectral types determinedfrom the Lyman continuum fluxes are consistent with opticaldeterminations. We have compared these Magellanic Cloud H II regionswith their Galactic counterparts in terms of size, rms electron densityand Lyman continuum flux. This comparison shows that their propertiesrelate to each other in the same way as those in Galactic H II regions.
| Near-Infrared Imaging Observations of the N159/N160 Complex in the Large Magellanic Cloud: Large Clusters of Herbig Ae/Be Stars and Sequential Cluster Formation
We have carried out deep near-infrared imaging observations of theN159/N160 star-forming region in the Large Magellanic Cloud. We observedan area of ~380 arcmin2 (~80,000 pc2 at thedistance of the LMC) in the J, H, and Ks bands. Theobservations are deep enough to detect Herbig Ae/Be stars down to ~3Msolar in the LMC. We discovered a total of 338 and 464candidate Herbig Ae/Be and OB stars, respectively, based on thenear-infrared colors and magnitudes. The Herbig Ae/Be candidatescomprise 10 clusters, the OB star candidates 13. We discovered anembedded Herbig Ae/Be cluster in the N159 East giant molecular cloud(GMC) and a Herbig Ae/Be cluster at the northeast tip of the N159 SouthGMC. Together with two neighboring H II regions, the Herbig Ae/Becluster at the tip of the N159S GMC provides a hint of the beginning ofsequential cluster formation in N159S. The spatial distributions of theHerbig Ae/Be and OB clusters, in conjunction with previously knownoptical clusters and embedded massive stars, indicate (1) sequentialcluster formation within each of the N159 and N160 star-forming regionsand (2) large-scale sequential cluster formation over the entireobserved region from N160 to N159S. Possible triggers for thelarge-scale cluster formation are the supergiant shell SGS 19 and anexpanding superbubble. Some of the Herbig Ae/Be clusters in theN159/N160 complex are significantly larger in spatial extent thanpre-main-sequence clusters of similar age in the Milky Way. Highlyturbulent gas motion in the LMC is probably responsible for forming thelarge young clusters.
| Australia Telescope Compact Array Survey of Candidate Ultracompact and Buried H II Regions in the Magellanic Clouds
We present a systematic survey for ultracompact (UC) H II regions in theMagellanic Clouds. Understanding the physics of massive star formation(MSF) is a critical astrophysical problem. The study of MSF began in ourGalaxy with surveys of UC H II regions, but before now this has not beendone for other galaxies. We selected candidates on the basis of theirInfrared Astronomical Satellite (IRAS) colors and imaged them at 3 and 6cm with the Australia Telescope Compact Array. Nearly all of theobserved regions contain compact radio sources consistent with thermalemission. Many of the sources are related to optically visible H IIregions, and often the radio emission traces the youngest and densestpart of the H II region. The luminosity function and number distributionof Lyman continuum fluxes of the compact radio sources are consistentwith standard stellar and cluster initial mass functions. This type ofsystematic assessment of IRAS diagnostics is important for interpretingSpitzer Space Telescope data, which will probe similar physical scalesin nearby galaxies as IRAS did in the Magellanic Clouds.
| OB stellar associations in the Large Magellanic Cloud: Survey of young stellar systems
The method developed by Gouliermis et al. (\cite{Gouliermis00}, PaperI), for the detection and classification of stellar systems in the LMC,was used for the identification of stellar associations and openclusters in the central area of the LMC. This method was applied on thestellar catalog produced from a scanned 1.2 m UK Schmidt Telescope Platein U with a field of view almost 6\fdg5 x 6\fdg5, centered on the Bar ofthis galaxy. The survey of the identified systems is presented herefollowed by the results of the investigation on their spatialdistribution and their structural parameters, as were estimatedaccording to our proposed methodology in Paper I. The detected openclusters and stellar associations show to form large filamentarystructures, which are often connected with the loci of HI shells. Thederived mean size of the stellar associations in this survey was foundto agree with the average size found previously by other authors, forstellar associations in different galaxies. This common size of about 80pc might represent a universal scale for the star formation process,whereas the parameter correlations of the detected loose systems supportthe distinction between open clusters and stellar associations.
| 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
| The Effects of Dust in Simple Environments: Large Magellanic Cloud H II Regions
We investigate the effects of dust on Large Magellanic Cloud (LMC)H II region spectral energy distributions usingarcminute-resolution far-ultraviolet (FUV), Hα, far-infrared(FIR), and radio images. Widely used indicators of the amount of lightlost to dust (attenuation) at Hα and in the FUV correlate witheach other, although often with substantial scatter. There are twointeresting systematic discrepancies: First, Hα attenuationsestimated from the Balmer decrement are lower than those estimated fromthe Hα-to-thermal radio luminosity ratio. Our data, at this stage,cannot unambiguously identify the source of this discrepancy. Second,the attenuation at 1500 Å and the UV spectral slope, β,correlate, although the slope and scatter are substantially differentfrom the correlation first derived for starbursting galaxies by Calzettiet al. Combining our result with those of Meurer et al. forultraluminous infrared galaxies and Calzetti et al. for starburstinggalaxies, we conclude that no single relation between β and 1500Å attenuation is applicable to all star-forming systems.
| 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.
| 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.
| The fourth catalogue of Population I Wolf-Rayet stars in the Large Magellanic Cloud
The catalogue provides for each of the 134 W-R stars of Population Ipresently known in the Large Magellanic Cloud, accurate equatorialcoordinates, photometric data, spectral classification, binary status,correlation with OB associations and HII regions. The miscellaneousdesignations of the stars are also listed. Although completeness is notpretended, results published during the last decade are highlighted inthe notes given for each individual star. A uniform set of findingcharts is presented. Figures 2 to 12 only in the electronic version athttp://edpsciences.com
| Extinction of H II regions in the Large Magellanic Cloud
The extinction properties of H II regions in the Large Magellanic Cloudare investigated using radio continuum data obtained from the MolongloObservatory Synthesis Telescope, digitized and calibrated H-alpha data,and published Balmer decrement measurements. The resultingextinction-color excess diagram suggests that (1) most H II regions inthe Magellanic Clouds have similar extinction properties to the Galacticones, (2) all imaginable gas/dust configurations are possible, and (3)the extinction of some highly reddened H II region cores originatesexternally in cocoon shells. The puzzle of different extinction-colorexcess ratios of Galactic and extragalactic H II regions is explained asbeing due to the different populations of observed samples rather thanany intrinsic differences. The extinction of the observed Galactic H IIregions produced by foreground dust overwhelms the internal extinction,while the situation in the observed extragalactic H II regions is justthe opposite.
| 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
| 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.
| 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.
| A comparison of far infrared and H-alpha emission of H-II regions in the Magellanic Clouds
From a comparison of the IRAS and smoothed H-alpha maps of theMagellanic Clouds, it was found that H-II regions with core-halostructure usually have higher F(60 microns)/F(H-alpha) ratios andprobably emit more in the far infrared than do extended low-density H-IIregions. This is consistent with the idea that the far infrared emissionis mainly produced by dust within H-II regions.
| A radio continuum study of the Magellanic Clouds. II - The far-infrared/radio correlation in the Large Magellanic Cloud
The correlation between the far-infrared (FIR) and the 6.3 cm radiocontinuum of the Large Magellanic Cloud (LMC) was studied. Radiocontinuum maps and infrared maps are presented. Statistical studiesindicated that the local point-by-point correlation between the two mapsis strong and appears to be due to the correlation between warm FIR andthermal radio emissions both of which are associated with young ionizingstars. The cool FIR/nonthermal radio correlation appears to be stronglylinked to the global FIR/radio correlation. A systematic difference wasobserved between the eastern and western half of the LMC. This asymmetrymay be due to different ages of massive stars or different gas-to dustratios in the two halves.
| A Comparison of Far Infrared and Hα Emission of HII Regions in the Magellanic Clouds
Not Available
| 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.
| Integrated UV magnitudes of the Large Magellanic Cloud associations
UV photographs (2600 A, 350 A passband) of the LMC have been obtained bythe S183 experiment during a Skylab mission. The background is estimatedand a method for deriving the integrated fluxes is presented. Theintegrated magnitudes of about 50 associations and isocontours of theirintensities are given, along with the B and V integrated magnitudes of13 associations.
| 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.
| Identification of LMC Clusters and Emission Line Objects in the HD and HDE Catalogues
Not Available
| Extinction and reddening of H II regions in the Large Magellanic Cloud
Absolute H-alpha and H-beta of H II regions in the Large MagellanicCloud are used in conjunction with radio continuum, 21-cm line, andstellar UBV data to study the dust associated with these regions.Various hypotheses concerning the optical properties and the spatialdistribution of the dust are examined, and the predicted characteristicsare compared with the observations. Uniform interstellar extinctioncannot explain the data. The following picture which is consistent withthe observations is suggested: some of the extinction is due to clumpeddust well outside of the emission zone, and the rest is caused by dustlocated closer to the ionized gas where scattering effects areimportant. This latter dust probably lies mostly just outside theboundary of the H II region, but some of the dust may be internal.
| 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.
| New-Wolf-Rayet stars in the Large Magellanic Cloud
Six new Wolf-Rayet stars located in the Large Magellanic Cloud have beendetected during searches of plates taken with the UK 1.2-m Schmidttelescope. Two of these are WN stars; three are WC. Five of the six havebeen confirmed by slit spectra. Two of the WC stars are close to 30Doradus and are approximately 3 mag fainter than any other known WC starin the LMC.
| The Identifications of HDE Objects with Large Magellanic Cloud Clusters and Nebulae
Not Available
| A catalogue of stellar associations in the Large Magellanic Cloud.
Abstract image available at:http://adsabs.harvard.edu/abs/1970AJ.....75..171L
| Rotation and Mass of the Large Magellanic Cloud.
Abstract image available at:http://adsabs.harvard.edu/abs/1960ApJ...131..265D
| Catalogues of Hα-EMISSION Stars and Nebulae in the Magellanic Clouds.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1956ApJS....2..315H&db_key=AST
| Large Magellanic Cloud.
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