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Massive young stellar objects in the Large Magellanic Cloud: water masers and ESO-VLT 3-4 μm spectroscopy
We investigate the conditions of star formation in the Large MagellanicCloud (LMC). We have conducted a survey for water maser emission arisingfrom massive young stellar objects in the 30 Doradus region (N157) andseveral other HII regions in the LMC (N105A, N113 and N160A). We haveidentified a new maser source in 30Dor at the systemic velocity of theLMC. We have obtained 3-4 μm spectra, with the European SouthernObservatory (ESO)-Very Large Telescope (VLT), of two candidate youngstellar objects. N105AIRS1 shows H recombination line emission, and itsSpectral Energy Distribution (SED) and mid-infrared colours areconsistent with a massive young star ionizing the molecular cloud.N157BIRS1 is identified as an embedded young object, based on its SEDand a tentative detection of water ice. The data on these four HIIregions are combined with mid-infrared archival images from the SpitzerSpace Telescope to study the location and nature of the embedded massiveyoung stellar objects and signatures of stellar feedback. Our analysisof 30Dor, N113 and N160A confirms the picture that the feedback from themassive O- and B-type stars, which creates the HII regions, alsotriggers further star formation on the interfaces of the ionized gas andthe surrounding molecular cloud. Although in the dense cloud N105A starformation seems to occur without evidence of massive star feedback, thegeneral conditions in the LMC seem favourable for sequential starformation as a result of feedback. In an Appendix, we present watermaser observations of the galactic red giants RDoradus and WHydrae.
| 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.
| Infrared Surface Brightness Fluctuations of Magellanic Star Clusters
We present surface brightness fluctuations (SBFs) in the near-IR for 191Magellanic star clusters available in the Second Incremental and All SkyData releases of the Two Micron All Sky Survey (2MASS) and compare themwith SBFs of Fornax Cluster galaxies and with predictions from stellarpopulation models as well. We also construct color-magnitude diagrams(CMDs) for these clusters using the 2MASS Point Source Catalog (PSC).Our goals are twofold. The first is to provide an empirical calibrationof near-IR SBFs, given that existing stellar population synthesis modelsare particularly discrepant in the near-IR. Second, whereas mostprevious SBF studies have focused on old, metal-rich populations, thisis the first application to a system with such a wide range of ages(~106 to more than 1010 yr, i.e., 4 orders ofmagnitude), at the same time that the clusters have a very narrow rangeof metallicities (Z~0.0006-0.01, i.e., 1 order of magnitude only). Sincestellar population synthesis models predict a more complex sensitivityof SBFs to metallicity and age in the near-IR than in the optical, thisanalysis offers a unique way of disentangling the effects of age andmetallicity. We find a satisfactory agreement between models and data.We also confirm that near-IR fluctuations and fluctuation colors aremostly driven by age in the Magellanic cluster populations and that inthis respect they constitute a sequence in which the Fornax Clustergalaxies fit adequately. Fluctuations are powered by red supergiantswith high-mass precursors in young populations and by intermediate-massstars populating the asymptotic giant branch in intermediate-agepopulations. For old populations, the trend with age of both fluctuationmagnitudes and colors can be explained straightforwardly by evolution inthe structure and morphology of the red giant branch. Moreover,fluctuation colors display a tendency to redden with age that can befitted by a straight line. For the star clusters only,(H-Ks)=(0.21+/-0.03)log(age)-(1.29+/-0.22) once galaxies areincluded, (H-Ks)=(0.20+/-0.02)log(age)-(1.25+/-0.16).Finally, we use for the first time a Poissonian approach to establishthe error bars of fluctuation measurements, instead of the customaryMonte Carlo simulations.This research has made use of the NASA/ IPAC Infrared Science Archive,which is operated by the Jet Propulsion Laboratory, California Instituteof Technology, under contract with the National Aeronautics and SpaceAdministration.
| 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.
| The relation between radio flux density and ionising ultra-violet flux for HII regions and supernova remnants in the Large Magellanic Cloud
We present a comparison between the Parkes radio surveys (Filipovic etal. 1995) and Vacuum Ultra-Violet (VUV) surveys (Smith et al. 1987) ofthe Large Magellanic Clouds (LMC). We have found 72 sources in common inthe LMC which are known HII regions (52) and supernova remnants (SNRs)(19). Some of these radio sources are associated with two or more UVstellar associations. A comparison of the radio flux densities andionising UV flux for HII regions shows a very good correlation, asexpected from theory. Many of the Magellanic Clouds (MCs) SNRs areembedded in HII regions, so there is also a relation between radio andUV which we attribute to the surrounding HII regions.
| Structure and Dynamics of Candidate O Star Bubbles in N44
Dynamical studies of superbubbles and Wolf-Rayet ring nebulae showdiscrepancies from the standard adiabatic model for windblown bubbles.We therefore study the physical properties and kinematics of threecandidate bubbles blown by single O stars to evaluate whether thesediscrepancies are also found in these simpler objects. Our samplecandidates are N44 F, N44 J, and N44 M, in the outskirts of the H IIcomplex N44 in the Large Magellanic Cloud. We have obtained ground-basedand Hubble Space Telescope emission-line images and high-dispersionechelle spectra for these objects. From the Hα luminosities andthe [O III]/Hα ratios of these nebulae, we estimate the spectraltypes of the ionizing stars to be O7 V, O9.5 V, and O9.5 V for N44 F,N44 J, and N44 M, respectively. We find that the observed expansionvelocity of 12 km s-1 for N44 F is consistent with thestellar wind luminosity expected from the central ionizing star, aspredicted by the standard bubble model. The observed upper limits forthe expansion velocities of N44 J and N44 M are also compatible with theexpected values, within the uncertainties. We also report the discoveryin N44 F of strongly defined dust columns, similar to those seen in theEagle Nebula. The photoevaporation of these dense dust features may bekinematically important and may actually govern the evolution of theshell. The inclusion of photoevaporation processes may thus underminethe apparent agreement between the observed bubble dynamics and thesimple adiabatic models.
| 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 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.
| The Multiphase Medium in the Interstellar Complex N44
We have obtained high-resolution H I observations of N44, one of thelargest H II complexes in the Large Magellanic Cloud. The distributionand internal motions of the H I gas show dynamic effects of fast stellarwinds and supernova blasts. Numerous H I holes are detected, with themost prominent two corresponding to the optically identifiedsuperbubbles Shell 1 and Shell 2. The H I gas associated with Shell 1shows an expansion pattern similar to that of the ionized gas shell, butthe mass and kinetic energy of the H I shell are 3-7 times those of theionized gas shell. The total kinetic energy of the neutral and ionizedgas of Shell 1 is still more than a factor of 5 lower than expected in apressure-driven superbubble. It is possible that the central OBassociation was formed in a molecular cloud, and a visible superbubblewas not fully developed until the ambient molecular gas had beendissociated and cleared away. This hypothesis is supported by theexistence of a molecular cloud toward N44 and the fact that the apparentdynamic age of the superbubble Shell 1 is much shorter than the age ofits OB association LH 47. Accelerated H I gas is detected at SNR0523-679. The mass and kinetic energy in the associated H I gas are alsomuch higher than those in the ionized gas of SNR 0523-679. Studies ofinterstellar gas dynamics using ionized gas alone are clearlyinadequate; neutral gas components must be included.
| A radio continuum study of the Magellanic Clouds. VIII. Discrete sources common to radio and infrared surveys of the Magellanic Clouds
We compare Parkes Telescope radio surveys with the IRAS Infrared (IR)surveys of the Magellanic Clouds (MCs). We find 130 discrete sources incommon towards the Large Magellanic Cloud (LMC) with both radio and IRemission. These 130 sources are mainly H Ii regions (89) and supernovaremnants (21). For 12 of the sources we have no identification and eightare background objects. We find 38 sources in common for the SmallMagellanic Cloud (SMC). Most of these sources are intrinsic (31) to theSMC, five sources are previously known background galaxies and twosources remain ambiguous. A flux density comparison of the radio and IRsources shows very good correlation and we note that the strongestsources at both radio and IR frequencies are H Ii regions. From theradio-IR comparison we propose that some 40 new sources in the LMC and10 in the SMC are H Ii regions or SNRs. All these new sources are alsoidentified in optical surveys.
| A radio continuum study of the Magellanic Clouds. VII. Discrete radio sources in the Magellanic Clouds
We present a study of discrete radio sources in the Magellanic Clouds(MCs) using the latest large-scale radio surveys made with the Parkesradio telescope between 1.4 and 8.55 GHz. These surveys achieved highersensitivity then previous surveys done with the Parkes telescope and sothe number of discrete radio sources detected towards the MCs hasincreased by factor of five. Also, we have obtained improved positions,flux densities and radio spectral indices for all of these sources. Atotal of 483 sources towards the Large Magellanic Cloud (LMC) and 224towards the Small Magellanic Cloud (SMC) have been detected at at leastone radio frequency. Most of the MC's sources have been classified inone of three groups: SNRs, H Ii regions or background sources accordingto classification criteria established here. In total, 209 discreteradio sources in the LMC and the 37 sources in the SMC are classifiedhere to be either H Ii regions or SNRs. We investigate their luminosityfunctions as well as the statistics of background sources behind theMCs. Also, we examine the distribution of SNRs and H Ii regions in theMCs. Tables 5 and 6 are only available electronically at the CDS via ftp130.79.128.5 or via http://cdsweb.u-strasbg.fr/Abstract.html
| 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.
| 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.
| 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.
| A Search for Methanol Masers in the Magellanic Clouds
We report the discovery of a second methanol maser in the LargeMagellanic Cloud and we present the results of synthesis observations ofthis and the methanol maser detected previously. The second discoverywas made using the Australia Telescope National Facility's 64-m Parkesradio telescope during an extensive maser search for 6.6-GHz maseremission from the 5_1_-6_0_ A^+^ transition in both Magellanic Clouds.Spectra were obtained towards 35 HII regions in the Large MagellanicCloud and 13 regions in the Small Magellanic Cloud, and also on a3-arcmin grid over an area 0.3^deg^ square, south of the 30 Doradusnebula. Parkes observations at 12.2 GHz towards the two maser sitesyielded no detectable emission from the 2_0_-3_-1_, E methanoltransition. The results suggest that methanol masers are less abundantin the Magellanic Clouds than in our Galaxy. Observations of the twomasers with the Australia Telescope Compact Array showed one to belocated near the continuum emission peak of the H II region MC18 (N11),while the other appeared to be centred near OH emission on thesouth-eastern boundary of MC23 (N105a).
| 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.
| X-rays from superbubbles in the Large Magellanic Cloud
Diffuse X-ray emission not associated with known supernova remnants(SNRs) are found in seven Large Magellanic Cloud H II complexesencompassing 10 OB associations: N44, N51D, N57A, N70, N154, N157 (30Dor), and N158. Their X-ray luminosities range from 7 x 10 to the 34thergs/s in N57A to 7 x 10 to the 36th ergs/s in 30 Dor. All, except 30Dor, have simple ring morphologies, indicating shell structures.Modeling these as superbubbles, it is found that the X-ray luminositiesexpected from their hot interiors fall an order of magnitude below theobserved values. SNRs close to the center of a superbubble add verylittle emission, but it is calculated that off-center SNRs hitting theionized shell could explain the observed emission.
| A new radio continuum survey of the Magellanic Clouds at 1.4 GHz. II - The radio morphology, and thermal and nonthermal emission of the LMC
The distribution of the radio continuum emission of the LMC is examined.The distribution of the spectral index and a reliable spectrum of theradio emission of the LMC are derived using radio continuum surveys ofthe LMC at 408, 1400, and 2300 MHz. The distribution of the spectralindex across the LMC shows a close positional agreement between flatspectrum and H-alpha emitting regions. The total nonthermal radioluminosity is derived, giving a total equipartition magnetic fieldstrength of about 6 microG. Accurate thermal radio flux densities of themost prominent LMC H II complexes are determined.
| A complete CO survey of the Large Magellanic Cloud
A complete CO survey of the central 6 deg x 6 deg of the LMC wasperformed in order to determine the distribution of molecular clouds. Atleast 10 percent of the region studied exhibits CO line emission, withpeak line temperatures of order 0.15 K. The emission is dominated by anextremely large complex of molecular clouds extending south from 30Doradus for nearly 2400 pc. There is an extended high-velocity COcomponent in the vicinity of 30 Doradus itself. Positions, masses, otherphysical characteristics, and related objects at other wavelengths aregiven for the 40 identified molecular clouds. The clouds follow arelation between CO luminosity and linewidth similar to that of Galacticclouds, but for a given linewidth appear about six times fainter,suggesting that CO luminosity scales roughly with metallicity orgas-to-dust ratio. The total mass of molecular clouds in the LMC isestimated to be 140 million solar, implying a ratio of molecular toatomic mass over the survey region of about 30 percent.
| A new radio continuum survey of the Magellanic Clouds at 1.4 GHz. I - Observations and data analysis
New radio continuum surveys of the Large and Small Magellanic Clouds at1.4 GHz have been made with the Parkes 64-m radio telescope with abeamwidth of 15.0 arcmin and an rms noise of about 30 mJy per beam areain the final maps. The observations are described and results presented.Their radio continuum morphology is discussed, and sources contained inboth fields are listed. The bulk of the sources resident within theradio boundaries of the Magellanic Clouds have flat spectra and can beassociated with bright H II regions. There is observational evidence inthe data to support tidal interactions between the Clouds, andlarge-scale structures are clearly observed in both galaxies.
| 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 calibration and age distribution for rich star clusters in the Large Magellanic Cloud
An empirical relation is presented for estimating the ages of rich starclusters in the Large Magellanic Cloud (LMC), to within a factor ofabout 2, from their integrated UBV colors. The calibration is based onpublished ages for 58 LMC clusters derived from main-sequencephotometry, integrated spectra, or the extent of the asymptotic giantbranches. Using stellar population models, a sample of LMC clusters moremassive than about 10,000 solar masses is isolated, which is correctedfor incompleteness as a function of magnitude. An unbiased agedistribution for three clusters is then determined. The number ofclusters decreases with increasing age in a manner that is qualitativelysimilar to the age distribution for the open clusters in our Galaxy. TheLMC age distribution is, however, flatter, and the median age of theclusters is greater. If the formation rate has been approximatelyconstant over the history of the two galaxies, then the age distributionobtained here implies that clusters are disrupted more slowly in theLMC. The results contain no evidence for bursts in the formation ofclusters, although fluctuations on small time scales and slow variationsover the lifetime of the LMC cannot be ruled out.
| 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.
| 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.
| The Identifications of HDE Objects with Large Magellanic Cloud Clusters and Nebulae
Not Available
| Observations of H2O maser emission in the Large Magellanic Cloud
A search for H2O maser emission towards 10 continuum sources in theLarge Magellanic Cloud was made with the Parkes radio telescope(beamwidth 1.7 arcmin). Maser emission was detected near three H IIregions, including the 30 Doradus nebula; the positions of the mainfeatures were estimated with an accuracy of + or - 15 arcsec. The maserluminosities were comparable to the typical value of H2O masers ingalactic H II regions. Upper intensity limits for maser emission in theremaining sources were 0.5 Jy. In contrast with previous observations,no emission was detected near N159.
| Supernova remnants in the Large Magellanic Cloud
Radio observations at 5 and 14.7 GHz are presented for 18 suggestedsupernova remnants in the Large Magellanic Cloud. We confirm that thereare non-thermal sources in 15 of these nebulae and that three of thesecontain two or more, possibly unrelated, non-thermal sources. Thesurface brightness diameter diagram for the LMC SNRs is only marginallydifferent from that for the galactic SNRs. The number-diameter diagramcan be interpreted in terms of the adiabatic (Sedov) model yielding asupernova birthrate of one every 400 yr in the LMC.
| Large Magellanic Cloud sources at 3.4-cm wavelength
Selected regions of the Large Magellanic Cloud have been surveyed atwavelength 3.4 cm with a 2.5 arcmin half-power beamwidth. Improvedspectral indices are given for 35 sources in the LMC area. Contour mapsof the 30 Doradus nebula and the four important sources to the south ofit are presented.
| 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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