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מאמרים קשורים
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
| 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.
| 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.
| 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.
| 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.
| A catalogue of compact radio sources in and behind the Large Magellanic Cloud
We present the results of a continuum snapshot survey of a 3 deg X 4 degregion of the Large Magellanic Cloud including the area of the giantmolecular cloud and the 30 Doradus nebula. The observations have beencarried out with the Australia Telescope Compact Array (ATCA) at 1.4 and2.4 GHz. Most fields are complete to about 6 mJy peak flux density at1.4 GHz and to about 3 mJy at 2.4 GHz. The positions, peak and integralflux densities of 113 compact (< 54") sources detected at 1.4 GHz andof 70 sources (<34") detected at 2.4 GHz are presented. Positions areaccurate to about 3" and peak flux densities are accurate to about 10%or better, depending on the source position relative to the pointingcenters. 32 of the sources detected at 1.4 GHz are coincident withHα objects in the catalogue of Davies et al.; these are possiblyintrinsic to the LMC. However, we suppose that most are backgroundobjects, since the number vs. flux agrees with predictions ofextragalactic source counts from other surveys. Tables 3 and 4 are alsoavailable electronically at the CDS via ftp cdsarc.u-strasbg.fr(130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html TheAustralia Telescope is funded by the Commonwealth of Australia foroperation as a National Facility managed by CSIRO.
| 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.
| 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.
| Abundances of the heavy elements in the Magellanic Clouds. II - H II regions and supernova remnants
The first consistent abundance analysis of both H II regions and SNRs inthe Magellanic Clouds is presented. Detailed modeling of the SNRsresults in abundance measures in good agreement with those from H IIregions, confirming the overall accuracy of the generalized modelingcode MAPPINGS for both photoionized and shock-excited nebulae. Adifferential analysis performed between SNRs and the GalacticHerbig-Haro (H-H) objects for elements heavier than Ar reveals thatthere is no difference for grain depletion in either Cloud SNR orGalactic H-H objects. It shows that there is no measurable zero pointerror between the Fe abundances determined from supergiants and thosedetermined from SNRs. This permits the two traditionally separatedabundance scales of the H II regions and supergiants to be combined forthe first time into one comprehensive system for the first time. Theimportance of this overall abundance pattern for the determination ofthe star formation history in the Clouds is addressed.
| 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.
| Identification of LMC Clusters and Emission Line Objects in the HD and HDE Catalogues
Not Available
| H II regions and star formation in the Magellanic Clouds
Photoelectrically calibrated maps of the H-alpha emission in theMagellanic Clouds have been used to measure integrated fluxes forseveral hundred H II regions and to study the properties of the H IIregion populations in the galaxies. The H II regions span a range of10,000 in luminosity, from objects on the scale of the Orion Nebula tothe 30 Doradus complex. The H-alpha luminosity function is wellrepresented over this entire range by a power law function, indicatingthat there is no characteristic luminosity scale for the H II regions.The distributions of nebular diameters, on the other hand, are fittedwell by exponential functions, with a scale length of 80 pc. Approximatefluxes for several of the extended filamentary networks in the galaxieshave also been measured. This extended component probability contributes15-25 percent of the total H-alpha luminosity of the galaxies.
| Absolute H-alpha and H-beta photometry of LMC H II regions
Absolute photoelectric H-alpha and H-beta photometry of 51 H II regionsand filaments in the LMC has been done. In this paper, theinstrumentation is described, the reduction procedures are explained,and the results are presented in the form of a catalog. A correspondingatlas is provided, showing photographs from the ESO red survey on whichobserved radio continuum contours and position indicators aresuperposed.
| 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 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.
| 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
| The spectrographic velocities of the bright-line nebulae.
Not Available
| Large Magellanic Cloud.
Not Available
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