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Results of the ESO-SEST Key Programme on CO in the Magellanic Clouds. X. CO emission from star formation regions in LMC and SMC
We present J=1-0 and J=2-1 12CO maps of several star-formingregions in both the Large and the Small Magellanic Cloud, and brieflydiscuss their structure. Many of the detected molecular clouds arerelatively isolated and quite small with dimensions of typically 20 pc.Some larger complexes have been detected, but in all cases the extent ofthe molecular clouds sampled by CO emission is significantly less thanthe extent of the ionized gas of the star-formation region. Very littlediffuse extended CO emission was seen; diffuse CO in between orsurrounding the detected discrete clouds is either very weak or absent.The majority of all LMC lines of sight detected in 13CO hasan isotopic emission ratio I( 12CO)/I( 13CO) ofabout 10, i.e. twice higher than found in Galactic star-formingcomplexes. At the lowest 12CO intensities, the spread ofisotopic emission ratios rapidly increases, low ratios representingrelatively dense and cold molecular gas and high ratios marking COphoto-dissociation at cloud edges.
| Determination of temperature of the ionizing stars of H II regions
The determination of temperature (T_eff) of the ionizing stars of H Iiregions was considered. In this work we used photoionization models forH Ii regions ionized by a single star to show that the index R=log ([OIi]lambda lambda 3726+3729/[O Iii]lambda 5007) can be used to estimateT_eff. The relation R vs. T_eff proved to be rather independent of thechemical abundances, but strongly dependent on the ionization parameterof the nebula. In order to check the reliability of using R fortemperature determination, we compared the values of T_eff obtained viathe index R for a sample of H Ii regions with data available in theliterature with independent estimations.
| X-Rays from Superbubbles in the Large Magellanic Cloud. VI. A Sample of Thirteen Superbubbles
We present ROSAT observations and analysis of thirteen superbubbles inthe Large Magellanic Cloud. Eleven of these observations have not beenpreviously reported. We have studied the X-ray morphology of thesuperbubbles and have extracted and analyzed their X-ray spectra.Diffuse X-ray emission is detected from each of these superbubbles, andX-ray emission is brighter than that theoretically expected for awind-blown bubble, suggesting that the X-ray emission from thesuperbubbles has been enhanced by interactions between the superbubbleshell and interior supernova remnants. We have also found significantpositive correlations between the X-ray luminosity of a superbubble andits Hα luminosity, expansion velocity, and OB star count. Further,we have found that a large fraction of the superbubbles in the sampleshow evidence of breakout regions, where hot X-ray-emitting gas extendsbeyond the Hα shell.
| An Empirical Test and Calibration of H II Region Diagnostics
We present spectrophotometry in the 3600-9700 Å region for asample of 39 H II regions in the Galaxy and Magellanic Clouds, for whichindependent information is available on the spectral types and effectivetemperatures of the ionizing stars. The spectra have been used toevaluate nebular diagnostics of stellar temperature, metal abundance,and ionization parameter, and to compare the observed behavior of theline indices with predictions of nebular photoionization models. Weobserve a strong degeneracy between forbidden-line sequences produced bychanges in stellar Teff and metal abundance, which severelycomplicates the application of many forbidden-line diagnostics toextragalactic H II regions. Our data confirm however that the Edmunds& Pagel [O II]+[O III] abundance index and the Vílchez &Pagel η' index provide more robust diagnostics of metalabundance and stellar effective temperature, respectively. A comparisonof the fractional helium ionization of the H II regions with stellartemperature confirms the reliability of the spectral type versusTeff calibration for the relevant temperature rangeTeff<=38,000 K. We use empirical relations between thenebular hardness indices and Teff to reinvestigate the casefor systematic variations in the stellar effective temperatures and theupper initial mass functions of massive stars in extragalactic H IIregions. The data are consistent with a significant softening of theionizing spectra (consistent with cooler stellar temperatures) withincreasing metal abundance, especially for Z<=Zsolar.However, unresolved degeneracies between Z and Teff stillcomplicate the interpretation of this result.
| Calibration of Nebular Emission-Line Diagnostics. I. Stellar Effective Temperatures
We present a detailed comparison of optical H II region spectra tophotoionization models based on modern stellar atmosphere models. Weexamine both spatially resolved and integrated emission-line spectra ofthe H II regions DEM L323, DEM L243, DEM L199, and DEM L301 in the LargeMagellanic Cloud. The published spectral classifications of the dominantstars range from O7 to WN3, and morphologies range from Strömgrensphere to shell structure. Two of the objects include SNR contamination.The overall agreement with the predictions is generally within 0.2 dexfor major diagnostic line ratios. An apparent pattern in the remainingdiscrepancies is that the predicted electron temperature is ~1000 Khotter than observed. [Ne III] intensities are also slightlyoverpredicted, which may or may not be related. We model the shockemission for the SNR-contaminated objects and find excellent agreementwith the observations for composite shock and photoionized spectra. DEML301's emission apparently results from both shocks and density-boundedphotoionization. The existence of contaminating shocks can be difficultto ascertain in the spatially integrated spectra. Our analysis of thecomplex DEM L199 allows a nebular emission-line test of unprecedenteddetail for WR atmospheres. Surprisingly, we find no nebular He IIλ4686 emission, despite the fact that both of the dominant WN3stars should be hot enough to fully ionize He I in their atmospheres.The nebular diagnostics are again in excellent agreement with the data,for stellar models not producing He+-ionizing photons. Theoptical diagnostics are furthermore quite insensitive to the ionizingenergy distribution for these early WR stars. We confirm that the η'emission-line parameter is not as useful as hoped for determining theionizing stellar effective temperature, T*. Both empiricallyand theoretically, we find that it is insensitive forT*>~40 kK and that it also varies spatially. Theshock-contaminated objects show that η' will also yield a spuriouslyhigh T* in the presence of shocks. It is furthermoresensitive to shell morphology. We suggest [Ne III]/Hβ as anadditional probe of T*. Although it is abundance dependent,[Ne III]/Hβ has higher sensitivity to T*, is independentof morphology, and is insensitive to shocks in our objects. Theseobservations should be useful data points for a first empiricalcalibration of nebular diagnostics of T*, which we attemptfor LMC metallicity.
| A study of the cool gas in the Large Magellanic Cloud. I. Properties of the cool atomic phase - a third H i absorption survey
The cool atomic interstellar medium of the Large Magellanic Cloud (LMC)seems to be quite different from that in the Milky Way. In a series ofthree papers we study the properties of the cool atomic hydrogen in theLMC (Paper I), its relation to molecular clouds usingSEST-CO-observations (Paper II) and the cooling mechanism of the atomicgas based on ISO-[\CII]-investigations (Paper III). In this paper wepresent the results of a third 21 cm absorption line survey toward theLMC carried out with the Australia Telescope Compact Array (ATCA). 20compact continuum sources, which are mainly in the direction of thesupergiant shell LMC 4, toward the surroundings of 30 Doradus and towardthe eastern steep \HI\ boundary, have been chosen from the 1.4 GHzsnapshot continuum survey of Marx et al. We have identified 20absorption features toward nine of the 20 sources. The properties of thecool \HI\ clouds are investigated and are compared for the differentregions of the LMC taking the results of Dickey et al. (survey 2) intoaccount. We find that the cool \HI\ gas in the LMC is either unusuallyabundant compared to the cool atomic phase of the Milky Way or the gasis clearly colder (\Tc\ ~ 30 K) than that in our Galaxy (\Tc\ ~ 60 K).The properties of atomic clouds toward 30 Doradus and LMC 4 suggest ahigher cooling rate in these regions compared to other parts of the LMC,probably due to an enhanced pressure near the shock fronts of LMC 4 and30 Doradus. The detected cool atomic gas toward the eastern steep \HI\boundary might be the result of a high compression of gas at the leadingedge.The Australia Telescope is funded by the Commonwealth of Australia foroperation as a National Facility managed by CSIRO.
| 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
| Physical Structure of Small Wolf-Rayet Ring Nebulae
We have selected the seven most well-defined Wolf-Rayet (WR) ringnebulae in the Large Magellanic Cloud (LMC), Br 2, 10, 13, 40a, 48, 52,and 100, to study their physical nature and evolutionary stages. New CCDimaging and echelle observations have been obtained for five of thesenebulae; previous photographic imaging and echelle observations areavailable for the remaining two nebulae. Using the nebular dynamics andabundances, we find that the Br 13 nebula is a circumstellar bubble, andthat the Br 2 nebula may represent a circumstellar bubble merging with afossil main-sequence interstellar bubble. The nebulae around Br 10, 52,and 100 all show influence of the ambient interstellar medium. Theirregular expansion patterns suggest that they still contain significantamounts of circumstellar material. Their nebular abundances would beextremely interesting, as their central stars are WC5 and WN3-WN4 starswhose nebular abundances have not been derived previously. Intriguingand tantalizing implications are obtained from comparisons of the LMC WRring nebulae with ring nebulae around Galactic WR stars, Galactic LBVs,LMC LBVs, and LMC BSGs; however, these implications may be limited bysmall-number statistics. A SNR candidate close to Br 2 is diagnosed byits large expansion velocity and nonthermal radio emission. There is noindication that Br 2's ring nebula interacts dynamically with this SNRcandidate.
| 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.
| Morphology and Physical Structure of the Interstellar Medium
The morphology of the interstellar medium (ISM) is dependent on thewavelength at which observations are made. Morphologies at differentwavelengths reveal interstellar gas components in different physicalconditions, thus allow us to probe the physical structure of the ISM.The global structure of the ISM is determined by the gravitationaleffects of the host galaxy itself and the environment. On scales from afew parsecs to 10^3 parsecs, the physical structure of the ISM islargely determined by the energy feedback from massive stars.Interactions between massive stars and the ISM not only shape the ISMbut also produce the multiple phases of the ISM. Multi-wavelengthobservations are needed to study the structure and evolution of amulti-phase ISM. The ISM of the Large Magellanic Cloud (LMC) is used toillustrate the environmental effects and the energy feedback frommassive stars. The energy feedback is more complex than any recipe candescribe.
| N 105 in the Large Magellanic Cloud: a newly evolved H II complex
The detailed radial velocity field of the H ii region N 105, in theLarge Magellanic Cloud, has been obtained for the Hα and [Oiii]5007 lines with a spatial sampling of 9'' and spectral ones of 16and 7 km s(-1) respectively. The line profiles present complex splittingand broadening in several places. The peculiar velocity field andmorphology indicate that N 105 contains four bubble shaped nebulae, andtwo bright distinct quasi spherical H ii regions, more or less coeval,embedded inside another large shell nebula. They are formed essentiallyby the action of the stellar winds of a few exciting stars, born deepinside their parental cloud. This result is deduced from the energyadded to the ionized gas by the stellar winds of early type stars andfrom dynamical simulations combining the effects of stellar winds withthose of high density gradients inside the neutral gas. The size and themorphology of the H ii region are conditioned by the depth inside thenatal cloud; the observed dynamic evolution of the H ii region starts atthe moment of blow out of the molecular cloud. The kinematics agreeswith the expected results from the stellar content and from themolecular studies. The positions of masers and of an infra-red (IR)source inside N 105 and the structure of this nebula suggest that suchan IR source may be the consequence of star formation triggered by thesurrounding wind pressure due to the progenitors of the presentlyevolved stars. Based on observations done at La Silla (ESO)
| Ultraviolet Imaging Telescope Observations of the Magellanic Clouds
We present wide-field far-ultraviolet (FUV; 1300-1800 Å) images ofthe Large and Small Magellanic Clouds (LMC, SMC). These data wereobtained by the Ultraviolet Imaging Telescope (UIT) during the Astro-1(1990 December 1-10) and Astro-2 (1995 March 2-18) missions; the imagesprovide an extensive FUV mosaic of the SMC and contain numerous regionsin the LMC, covering a wide range of stellar densities and current starformation activity. A total of 47 LMC/Lucke-Hodge and 37 SMC/Hodge OBassociations are completely or partially included in the observedfields. FUV data can identify the hottest OB stars more easily than canoptical photometry, and these stars dominate the ionizing flux, which iscorrelated to the observed Hα flux of the associated H ii regions.Of the H ii regions in the catalog of Davies, Elliott, & Meaburn(DEM), the UIT fields completely or partially include 102 DEM regions inthe LMC and 74 DEM regions in the SMC. We present a catalog of FUVmagnitudes derived from point-spread function photometry for 37,333stars in the LMC (the UIT FUV magnitudes for 11,306 stars in the SMCwere presented recently by Cornett et al.), with a completeness limit ofm_UV ~ 15 mag and a detection limit of m_UV ~ 17.5. The averageuncertainty in the photometry is ~0.1 mag. The full catalog withastrometric positions, photometry, and other information is alsoavailable from publicly accessible astronomical data archives. We dividethe catalog into field stars and stars that are in DEM regions. Weanalyze each of these two sets of stars independently, comparing thecomposite UV luminosity function of our data with UV magnitudes derivedfrom stellar evolution and atmosphere models in order to derive theunderlying stellar formation parameters. We find a most probable initialmass function (IMF) slope for the LMC field stars of Gamma = -1.80 +/-0.09. The statistical significance of this single slope for the LMCfield stars is extremely high, though we also find some evidence for afield star IMF slope of Gamma ~ -1.4, roughly equal to the Salpeterslope. However, in the case of the stars in the DEM regions (the starsin all the regions were analyzed together as a single group), we findthree IMF slopes of roughly equal likelihood: Gamma = -1.0, -1.6, and-2.0. No typical age for the field stars is found in our data for timeperiods up to a continuous star formation age of 500 Myr, which is themaximum age consistent with the completeness limit magnitude of thecatalog's luminosity function. The best age for the collection ofcluster stars was found to be t_0 = 3.4 +/- 1.9 Myr; this is consistentwith the age expected for a collection of OB stars from many differentclusters.
| 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.
| 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.
| Gas motions in and origin of the supergiant shell LMC4.
IUE high-dispersion spectra of stars in the supergiant shell LMC4havebeen used to derive velocities and column densities of absorbing gasclouds. The HI 21-cm profiles for the LMC4region from the LMC data ofRohlfs et al. (1984) have been analysed and interpreted in cloudcomponents. Combining the absorption and emission line data, a detailedpicture emerges of the location along the line of sight of the variousgas components and of the stars. LMC4 has a systemic velocity of285km/s. A pocket of gas in the center of LMC4is found to be receding at~325km/s while over the entire area we find gas near 260km/s. These twocomponents of gas differ in various ways. We argue that the gas at325km/s most likely belongs to a shell breakup. The gas at 260km/sprobably does not belong to the LMC4but lies in front of the supershell.There is no evidence for a systematic radial expansion of the gas fromthe geometric center of LMC4. Also, there is gas near 220km/s found inseveral of the IUE spectra. Given that the velocity differs by 65km/sfrom that of the main body of LMC4and the large spatial extent wepropose this gas cloud to be in the Milky Way halo. Our results arecompared with several theoretical scenarios for superbubble structures.We conclude that the origin of LMC4 is best explained by a process ofself-propagating star formation. Our data are in agreement withexpansion velocities around 10km/s.
| 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.
| Dust in emission nebulae of the LMC derived from photometric reddening of stars
VBLUW photometric observations of stars in emission nebulae of the LMCare reported. The luminosities and extinctions of the stars are derived.Agreement is found between the average photometric extinctions of thenebulae and the extinctions derived from the Balmer line decrementmeasured by Caplan and Deharveng (1985 and 1986). The photometricextinctions are shown in the CO map of the LMC (Cohen et al., 1988).
| 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.
| 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.
| Ring nebulae associated with Wolf-Rayet stars in the Large Magellanic Cloud. III - Kinematics of DEM 39, 231, 240, and 315
Echellograms with 4.6 A per mm dispersion have been obtained for fourring nebulae around Wolf-Rayet stars in the Large Magellanic Cloud(LMC): DEM 39, 231, 240, and 315. Their nature is analyzed and reportedhere. DEM 39 and DEM 315 are stellar wind blown bubbles, DEM 231 isprobably an expanding hemisphere formed by the central star notnecessarily during its W-R phase, and DEM 240 may have resulted from theinteraction of stellar wind with a sheet of moving gas. A comparison ofthe bubbles blown by W-R stars in the Galaxy and the LMC is also made.
| The dynamics of two giant interstellar shells in the LMC
The motions of the neutral and ionized gas associated with two nebularshells within the LMC have been investigated by observing the profilesof the Na I and Ca II interstellar absorption lines in a central star,and those of the O II forbidden emission lines over the nebulae. Up toseven components over a range of heliocentric radial velocities from 260to 340 km/s were discovered. Stellar winds and supernova explosions areboth considered as possible mechanisms for the formation of theseshells, but many features of the trends in radial velocity over theirsurfaces are not easily explained by these mechanisms.
| 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.
| 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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