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.
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Early-type variables in the Magellanic Clouds. I. beta Cephei stars in the LMC bar
A thorough analysis of the OGLE-II time-series photometry of the LargeMagellanic Cloud bar supplemented by similar data from the MACHOdatabase led us to the discovery of three beta Cephei-type stars. Theseare the first known extragalactic beta Cephei-type stars. Two of thethree stars are multiperiodic. Two stars have inferred masses of about10 M_sun while the third is about 2 mag brighter and at least twice asmassive. All three variables are located in or very close to the massiveand young LMC associations (LH 41, 59 and 81). It is therefore veryprobable that the variables have higher than average metallicities. Thiswould reconcile our finding with theoretical predictions of the shapeand location of the beta Cephei instability strip in the H-R diagram.The low number of beta Cephei stars found in the LMC is anotherobservational confirmation of strong dependence of the mechanism drivingpulsations in these variables on metallicity. Follow-up spectroscopicdetermination of the metallicities in the discovered variables willprovide a good test for the theory of pulsational stability in massivemain-sequence stars.
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The Optical Gravitational Lensing Experiment. Catalog of Star Clusters from the Large Magellanic Cloud
We present the catalog of star clusters found in the area of about 5.8square degree in the central regions of the Large Magellanic Cloud. Itcontains data for 745 clusters. 126 of them are new objects. For eachcluster equatorial coordinates, radius, approximate number of membersand cross-identification are provided. Photometric data for all clusterspresented in the catalog and Atlas consisting of finding charts andcolor-magnitude diagrams are available electronically from the OGLEInternet archive.
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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.
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A survey of SiO emission towards interstellar masers. I. SiO line characteristics
We have conducted a survey of SiO emission towards galactic H_2O and OHmasers and ultracompact HII regions using the 15-m SEST and the 20-mOnsala telescope. With the SEST the transitions (v=0,J=2-1) and(v=0,J=3-2) of SiO at 3 and 2 mm were measured simultaneously. WithOnsala only the (v=0,J=2-1) line was accessible. Altogether 369 objectswere observed and SiO was detected towards 137 of them. The detectionrate is highest towards the most intense H_2O masers, which probablyrequire powerful shocks to be excited. The SiO detection rate correlatesalso with the integrated far-infrared flux density and the FIRluminosity of the associated IRAS point source, indicating that theoccurrence of shocks is related to the amount of radiation from thecentral stellar source(s). For flux and luminosity limited samples theSiO detection rate is higher in the inner 7 kpc from the galactic centrethan elsewhere. This suggests that dense cores belonging to the socalled ``molecular ring" provide particularly favourable conditions forthe production of gaseous SiO. The full widths above 2sigma of theSiO(J=2-1) lines, which are likely to be related to the associated shockvelocities, range from 2 to 60 km s(-1) except for the line in Ori KLwhich has a full width of about 100 km s(-1) . The median of our sampleis 19 km s(-1) . The SiO lines are single-peaked and the peak velocitiesare always close to the ambient cloud velocity as determined frompublished CS observations. These line characteristics are compared withthe predictions of kinematical bow-shock models. The SiO line shapescorrespond with the model of \cite[Raga & Cabrit (1993)]{R93} wherethe emission arises from turbulent wakes behind bow-shocks. However, thenumber of symmetric, relatively narrow profiles indicates that at leastin some of the observed sources SiO emission arises also from thequiescent gas component. We suggest that this is due to evaporation ofsilicon compounds from grain mantles and their reprocessing to SiO indense quiescent gas according to the model of \cite[McKay (1995,1996).]{M95} These reactions may be initiated and sustained by ionizingradiation from shocks, in the same way as the enhancement of HCO(+) nearHerbig-Haro objects has been explained in the model of \cite[Wolfire& Koenigl (1993).]{W93} The excitation temperatures of SiO(J=2-1)and (J=3-2) transitions were determined towards three strong sourcesusing measurements in isotopically substituted SiO. In all three sourcesthe transitions are clearly subthermally excited, implying moderatedensities (< 3 10(6) cm(-3) ) in the SiO emission regions. The entireTables~B.1 and B.2 and the spectra of all the detected SiO sources areonly available in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
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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.
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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.
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A CS and NH 3 Survey of Regions with H 2O Maser Emission
Abstract image available at:http://adsabs.harvard.edu/abs/1996ApJ...463..205A
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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.
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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.
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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.
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Bar star clusters in the LMC - Formation history from UBV integrated photometry
The sample of star clusters in the LMC Bar region with integrated UBVphotometry was enlarged by approximately a factor four, totaling 129objects. The (B-V) histogram gap between blue and red clustersdisappears with this deeper sample. Age groups in terms of equivalentSWB types were derived and their spatial distribution studied. Clustersyounger than t about 200 Myr are not homogeneously distributed throughthe bar. In particular a strong star forming event at t about 100 Myrwas detected in the eastern part of the Bar, consisting of a compactgrouping of seven coeval clusters around NGC 2058 and NGC 2065. Also, 11close pairs and two trios are analyzed, and the colors indicate thatonly four pairs are clearly not coeval.
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A Morphological Criterion for Distinguishing Between Supernova Remnants and HII Regions
A variant of the vector discriminant pattern recognition technique isapplied to UK Schmidt telescope images of nebulae in the LargeMagellanic Cloud. A criterion is thereby obtained which may be appliedgenerally to distinguish between supernova remnants (SNRs) and H IIregions from their optical images. Furthermore, two nebulae previouslyidentified as H II regions are now interpreted as SNRs.
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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.
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Observed dynamical parameters of the disk clusters of the LMC. I
A study of the observed dynamical parameters of 32 globular clusters ofthe LMC disk has been carried out by means of star counts. The clusterswere measured on a set of three plates (J, V, I) taken with the 1.2 mU.K. Schmidt Telescope. The derived tidal radii were all found to belarge within a very narrow range. As a consequence the range of thetotal masses was found to be very narrow as well. These two parametersare large in comparison to those of the disk young clusters of thegalaxy but they are similar to the dimensions of the halo galacticglobulars.
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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.
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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.
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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.
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A Catalogue of Clusters in The LMC
Not Available
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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
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