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 The Role of Evolutionary Age and Metallicity in the Formation of Classical Be Circumstellar Disks. I. New Candidate Be Stars in the LMC, SMC, and Milky WayWe present B, V, R, and Hα photometry of eight clusters in theSmall Magellanic Cloud, five in the Large Magellanic Cloud, and threeGalactic clusters and use two-color diagrams (2-CDs) to identifycandidate Be star populations in these clusters. We find evidence thatthe Be phenomenon is enhanced in low-metallicity environments, based onthe observed fractional early-type candidate Be star content of clustersof age 10-25 Myr. Numerous candidate Be stars of spectral types B0-B5were identified in clusters of age 5-8 Myr, challenging the suggestionof Fabregat & Torrejon that classical Be stars should only be foundin clusters at least 10 Myr old. These results suggest that asignificant number of B-type stars must emerge onto the zero-age mainsequence as rapid rotators. We also detect an enhancement in thefractional content of early-type candidate Be stars in clusters of age10-25 Myr, suggesting that the Be phenomenon does become more prevalentwith evolutionary age. We briefly discuss the mechanisms that mightcontribute to such an evolutionary effect. A discussion of thelimitations of using the 2-CD technique to investigate the roleevolutionary age and/or metallicity play in the development of the Bephenomenon is offered, and we provide evidence that other B-type objectsof very different nature, such as candidate Herbig Ae/Be stars, maycontaminate the claimed detections of Be stars via 2-CDs. An ATCA radio-continuum study of the Small Magellanic Cloud - III. Supernova remnants and their environmentsA total of 717 sources from the Australia Telescope Compact Array (ATCA)catalogue of the Small Magellanic Cloud (SMC) have been classified inPaper II (of this series) by Payne et al. Here, we present a statisticalanalysis of all 16 confirmed supernova remnants (SNRs) and five newcandidate remnants. Included is a detailed discussion of the latter andthree other sources that have some SNR characteristics. We have alsofound a new microquasar candidate (ATCA J005523-721055) in addition toATCA J004718-723947 reported in Paper II. Source diameter comparisonssuggest that SNRs as a group are of similar size in radio, optical andX-ray with surface brightness values in the range of Galactic remnants.Remnant spectral indices, α[defined asSν~να, with Sν (fluxdensity) and ν (frequency)], have a mean of -0.63 [standard deviation(s.d.) = 0.43] and ROSAT X-ray hardness ratios confirm them to be softX-ray sources compared to background objects. We could not find anymeaningful correlation between SNR surface brightness and diameter; wealso discuss the number-diameter relation. A Venn diagram summarizesthat most SNRs emit radiation in all three of the radio, optical andX-ray domains. HII region diameter comparisons between radio and opticalsources show them to be a very diverse group that defies any simplerelationship, preventing any meaningful calculation of flux density orspectral index. To better understand environments containing SNRs, wehave scaled Hα images of four SMC regions and subtracted theirflux from the ATCA 2.37-GHz radio image. These 2.37 GHz-Hαsubtraction (or difference) images reveal some new sources withpredominantly non-thermal emission, exposing SNRs confused with HIIregions. Triggered star formation in the inner wing of the SMC. Two possible supernova explosions in the N83-84-85 regionIn this article we study the N83-84-85 region of the inner wing of theSMC. Direct and low-dispersion objective prism plates taken with the 1.2m UK Schmidt Telescope have been digitized by the SuperCOSMOS machine.Star counts have been performed for our region in selected luminosityslices in the U filter and isodensity contours have been used toidentify the structures with enhanced stellar number density. We findevidence of triggered star formation from massive stars of older to morerecent OB associations. Circular arcs constructed by O and B stars havebeen detected. A study of the population places stars with more recentages in the groups of the arcs than of their centers. These effects canbe explained by supernova explosions. A catalogue of the non-saturateddetected OB stars in this region is given.Table \ref{t3} is only available in electronic form athttp://www.edpsciences.org Hubble Space Telescope Observations of Three Very Young Star Clusters in the Small Magellanic CloudWe present Space Telescope Imaging Spectrograph (STIS) broadband imageryand optical slitless spectroscopy of three young star clusters in theSmall Magellanic Cloud (SMC). MA 1796 and MG 2 were previously known asplanetary nebulae and were observed as such in our Hubble SpaceTelescope (HST) survey. With the HST spatial resolution, we show thatthey are instead H II regions, surrounding very young star clusters. Athird compact H II region, MA 1797, was serendipitously observed by ussince it falls in the same frame of MA 1796. A limited nebular analysisis presented as derived from the slitless spectra. We find that MA 1796and MG 2 are very heavily extincted, with c>=1.4, defining them asthe most extincted optically discovered star-forming regions in the SMC.MA 1796 and MG 2 are extremely compact (less than 1 pc across), while MA1797, with diameter of about 3 pc, is similar to the ultracompact H IIregions already known in the SMC. Stellar analysis is presented, andapproximate reddening correction for the stars is derived from theBalmer decrement. Limited analysis of their stellar content and theirionized radiation shows that these compact H II regions are ionized bysmall stellar clusters whose hottest stars are at most of the B0 class.These very compact, extremely reddened, and probably very dense H IIregions in the SMC offer insight into the most recent star formationepisodes in a very low metallicity galaxy.Based on observations made with the NASA/ESA Hubble Space Telescope,obtained at the Space Telescope Science Institute, which is operated bythe Association of Universities for Research in Astronomy, Inc., underNASA contract NAS5-26555. Unusual CO Line Ratios and Kinematics in the N83/N84 Region of the Small Magellanic CloudWe present new CO (1-->0) and (2-->1) observations of the N83/N84molecular cloud complex in the southeast wing of the Small MagellanicCloud (SMC). While the (2-->1)/(1-->0) integrated line brightnessratio (in temperature units) is uniformly 1.1 throughout most of thecomplex, we find two distinct regions with unusually high ratios,(2-->1)/(1-->0)>~2. These regions are associated with the N84Dnebula and with the inside of the 50 pc expanding molecular shell N83.This shell is spatially coincident with the NGC 456 stellar associationand the HFPK2000-448 radio continuum/X-ray source, tentativelyclassified as a supernova remnant. We explore possible causes for thehigh ratios observed and conclude that the CO emission probably arisesfrom an ensemble of small (R~0.1 pc), warm (Tg~40 K) clumps.Analysis of the CO shell parameters suggests that it is wind driven andhas an age of slightly more than 2 million years. We have also used thisdata set to determine the CO-to-H2 conversion factor in theSMC, an especially interesting measurement because of the lowmetallicity of this source (~1/9 solar). Surprisingly, after comparingthe CO luminosities of clouds in N83/N84 with their virial masses, wefind a CO-to-H2 conversion factor XCO only 1.9times larger than what we obtain when applying the same algorithm tosolar metallicity clouds in the Milky Way and M33. This result fits intothe emerging pattern that CO observations with high linear resolutionsuggest nearly Galactic values of XCO in a wide range ofenvironments. Results of the ESO-SEST Key Programme on CO in the Magellanic Clouds. X. CO emission from star formation regions in LMC and SMCWe 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. The Small Magellanic Cloud in the far infrared. I. ISO's 170 mu m map and revisit of the IRAS 12-100 mu m dataThe ISOPHOT experiment onboard the ISO satellite generated a completeview of the Small Magellanic Cloud (SMC) at 170 mu m with 1.5 arcminresolution. The map is analysed using an automated photometry programenabling accurate photometric characterization of the far infrared (FIR)emitting regions. An integrated FIR luminosity of 8.5x 107Lsun is obtained, leading to a star formation rate ofSFRFIR=0.015 Msun/yr. With an average dusttemperature of , the total dustmass follows to MD=3.7x105 Msun. Inthis paper, the sources detected at 170 mu m are compared with thoseobtainable from the IRAS satellite data. For this purpose, the 12 mu m,25 mu m, 60 mu m, and 100 mu m IRAS high resolution (HiRes) maps of theSMC are re-examined using the same method. In contrast to formerstudies, this provides an all-band ISO/IRAS source catalog which is nolonger based on eyeball classification, but relies on an algorithm whichis capable of automated, repeatable photometry, even for irregularsources. In the mid infrared IRAS bands numerous bright FIR emittingregions in the SMC are detected and classified: 73 sources are found at12 mu m, 135 at 25 mu m (most of them with Fnu <1.0 Jy).All three FIR bands at 170 mu m, 100 mu m, and 60 mu m reproduce theoverall morphological structure of the SMC similarly well, in contrastto the 12 mu m and 25 mu m maps which only contain a limited number ofextended sources and do not trace the main body of the SMC. 243 sourcesare detected in the ISO 170 mu m map, 155 of them with Fnu>=2.0 Jy. Comparable numbers are found for the two FIR IRASmaps at 60 mu m (384) and 100 mu m (338) with fluxes up to 450 Jy. 70 ofthe 243 170 mu m sources are assigned a general SED type (cold'',warm'', i.e., <30 K, >30 K) for the first time. A comparisonwith earlier IRAS results suggests that many source flux densities inthose studies have been under- or overestimated because ofnon-standardized fitting methods. Many sources with flux densities up to40 Jy listed in former catalogs cannot be identified in our data.Based on observations with ISO, an ESA project with instruments fundedby ESA Member States (especially the PI countries: France, Germany, TheNetherlands and the UK) and with the participation of ISAS and NASA.The tables in Appendices A to E are only available in electronic form atthe 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/401/873} On the origin of nitrogenThe problem of the origin of nitrogen is considered within the frameworkof an empirical approach. The oxygen abundances and nitrogen to oxygenabundances ratios are derived in H II regions of a number of spiralgalaxies through the recently suggested P-method using more than sixhundred published spectra. The N/O-O/H diagram for H II regions inirregular and spiral galaxies is constructed. It is found that the N/Ovalues in H II regions of spiral galaxies of early morphological typesare higher than those in H II regions with the same metallicity inspiral galaxies of late morphological types. This suggests along-time-delayed contribution to the nitrogen production. The N/O ratioof a galaxy can then be used as an indicator of the time that haselapsed since the bulk of star formation occurred, or in other words ofthe nominal age'' of the galaxy as suggested by Edmunds & Pagelmore than twenty years ago. The scatter in N/O values at a given O/H canbe naturally explained by differences in star formation histories ingalaxies. While low-metallicity dwarf galaxies with low N/O do notcontain an appreciable amount of old stars, low-metallicity dwarfgalaxies with an appreciable fraction of old stars have high N/O.Consideration of planetary nebulae in the Small Magellanic Cloud and inthe Milky Way Galaxy suggests that the contribution of low-mass stars tothe nitrogen production is significant, confirming the conclusion thatthere is a long-time-delayed contribution to the nitrogen production. Automatic extraction and classification of low-dispersion objective prism stellar spectraThe observing material used for this task is prism spectral plates takenwith Schmidt-class telescopes. Such a plate generally contains thousandsof spectra, and there are prism-plate libraries and digitized databasesin several astronomical centers that can be exploited for this analysis.After a successive detection from the prism plate image, the spectra areautomaticaly extracted in one-dimensional streams containing all thebasic information. These spectra require automated classificationmethods to be analyzed in an objective form. In this article we comparetwo classification methods directly applied to stellar spectra: a linearcorrelation and a minimum distance method. Obscured AGB stars in the Magellanic Clouds. I. IRAS candidatesWe have selected 198 IRAS sources in the Large Magellanic Cloud, and 11in the Small Magellanic Cloud, which are the best candidates to bemass--loosing AGB stars (or possibly post--AGB stars). We used thecatalogues of \cite[Schwering \& Israel (1990)]{ref42} and\cite[Reid et al. (1990)]{ref36}. They are based on the IRAS pointedobservations and have lower detection limits than the Point SourceCatalogue. We also made cross-identifications between IRAS sources andoptical catalogues. Our resulting catalogue is divided in 7 tables.Table \ref{tab1} lists optically known red supergiants and AGB stars forwhich we found an IRAS counterpart (7 and 52 stars in the SMC and LMC,respectively). Table \ref{tab2} lists obscured'' (or cocoon'') AGBstars or late-type supergiants which have been identified as such inprevious works through their IRAS counterpart and JHKLM photometry (2SMC and 34 LMC sources; no optical counterparts). Table \ref{tab3} listsknown planetary nebulae with an IRAS counterpart (4 SMC and 19 LMC PNe).Table \ref{tab4} lists unidentified IRAS sources that we believe to begood AGB or post--AGB or PNe candidates (11 SMC and 198 LMC sources).Table~\ref{tab5} lists unidentified IRAS sources which could be any typeof object (23 SMC and 121 LMC sources). Table \ref{tab6} lists IRASsources associated with foreground stars (29 SMC and 135 LMC stars).Table \ref{tab7} lists ruled out IRAS sources associated with HIIregions, hot stars, etc... We show that the sample of IRAS AGB stars inthe Magellanic Clouds is very incomplete. Only AGB stars more luminousthan typically 10^4 L_\odot and with a mass-loss rate larger thantypically 5 10^{-6} M_\odot/yr could be detected by the IRAS satellite.As a consequence, one expects to find very few carbon stars in the IRASsample. We also expect that most AGB stars with intermediate mass--lossrates have not been discovered yet, neither in optical surveys, nor inthe IRAS survey. Tables 1 to 8 are also available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html Gamma-Ray Line Signals from 26Al and 60Fe in the Galaxies of the Local GroupSteady state gamma -line fluxes from the decay of 26Al and 60Fe situatedin the Local Group galaxies LMC, SMC, NGC 6822, IC 1613, M31, and M33are estimated with standard supernova yields and supernova rates basedon blue luminosities and other indicators of massive star formation. Thelargest 26Al flux, 2.0 x 10-6 gamma s-1 cm-2, comes from the LMC, whilethe SMC is estimated to provide an 26Al flux of 3.6 x 10-7 gamma s-1cm-2. Andromeda is surprisingly weak, only about 1.6 x 10-8 gamma s-1cm-2 because of both its distance and its current low rate of starformation. Expected 60Fe fluxes are about 16% of the 26Al flux.Detection of these fluxes is feasible but will probably requiresensitivities greater than those of the International Gamma-RayAstrophysical Laboratory mission. The chief utility of such observationsis the new insight they provide into the mechanisms of supernovaexplosions, the distribution and nature of massive-star--forming regionsin irregular and spiral galaxies, and the nucleosynthetic history ofLocal Group members. A radio continuum study of the Magellanic Clouds V. Catalogues of radio sources in the Small Magellanic Cloud at 1.42, 2.45, 4.75, 4.85 and 8.55 GHzWe present catalogues of radio sources in the Small Magellanic Cloudfrom observations with the Parkes radio telescope at 1.42, 2.45, 4.75and 8.55 GHz, and an additional catalogue from the Parkes-MIT-NRAOsurvey at 4.85 GHz. A total of 224 sources were detected at at least oneof these frequencies, 60 of which are reported here for the first timeas radio sources. We compare positions and flux densities of thesesources with previously published results and find no significantpositional displacement or flux discrepancies. Tables 2-7 are onlyavailable electronically at the CDS via ftp 130.79.128.5 or athttp://cdsweb.u-strasbg.fr/Abstract.html Extinction and reddening of HII regions in the Small Magellanic Cloud.We present absolute Hα and Hβ fluxes, obtained with aFabry-Perot spectrophotometer, of 24 bright HII regions in the SmallMagellanic Cloud. The photographic Hα maps of Kennicutt &Hodge (1986) are re-calibrated using these new Hα fluxes; the newcalibration gives fluxes 25% smaller than those previously published.These photographic and photoelectric Hα data are used inconjunction with radio continuum observations at 843 MHz from theMolonglo Observatory Synthesis Telescope to study the dust associatedwith SMC HII regions. For most regions the derived reddenings andextinctions are compatible with the standard Galactic extinction law anduniform interstellar extinction. A few regions display relatively highreddening and extinction; these are bright compact sources, such asN13AB, N27 and the cores of N81 and N88, all of which probably haveclosely associated dust. Low resolution Hi observations do not detectthese high concentrations of dust. A Revised and Extended Catalog of Magellanic System Clusters, Associations, and Emission Nebulae. I. Small Magellanic Cloud and BridgeA survey of extended objects in the Magellanic System was carried out onthe ESO/SERC R and J Sky Survey Atlases. The present work is dedicatedto the Small Magellanic Cloud and to the inter-Magellanic Cloud region("Bridge") totaling 1188 objects, of which 554 are classified as starclusters, 343 are emissionless associations, and 291 are related toemission nebulae. The survey includes cross-identifications amongcatalogs, and we present 284 new objects. We provide accurate positions,classification, homogeneous sizes, and position angles, as well asinformation on cluster pairs and hierarchical relation for superimposedobjects. Two clumps of extended objects in the Bridge and one at theSmall Magellanic Cloud wing tip might be currently forming dwarfspheroidal galaxies. Blue-violet spectral evolution of young Magellanic Cloud clustersWe 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. Ultraviolet spectral evolution of star clusters in the IUE library.The ultraviolet integrated spectra of star clusters and H II regions inthe IUE library have been classified into groups based on their spectralappearance, as well as on age and metallicity information from otherstudies. We have coadded the spectra in these groups according to theirS/N ratio, creating a library of template spectra for futureapplications in population syntheses in galaxies. We define spectralwindows for equivalent width measurements and for continuum tracings.These measurements in the spectra of the templates are studied as afunction of age and metallicity. We indicate the windows with a strongmetallicity dependence, at different age stages. The initial mass function for massive stars in the Magellanic Clouds. 2: Interstellar reddening toward 14 OB associationsWe have used UBV CCD photometry to determine the interstellar reddeningtoward 14 OB associations in the Magellanic Clouds. The tworeddening-free indices available in the UBV system were used to obtainthe reddening estimates. The mean color excesses of the associationsrange from E(B-V) = 0.01-0.26 mag in the Large Magellanic Cloud (LMC)and from E(B-V) = 0.06-0.25 mag in the Small Magellanic Cloud (SMC). Wehave modeled the observed scatter in the color excesses of individualstars within the associations and find that statisically significantdifferential reddening exists in at least some of the associations. The initial mass function for massive stars in the Magellanic Clouds. 1: UBV photometry and color-magnitude diagrams for 14 OB associationsUBV charge coupled device (CCD) photometry has been obtained for 14 OBassociations in the Magellanic Clouds using the University of Toronto's0.6 m telescope and the Carnegie Institution of Washington's 1.0 mreflector, both on Las Campanas, Chile. The data are presented and usedto construct color-magnitude diagrams for the purposes of investigatingthe massive-star content of the associations. A New Catalogue of Hα Emission Line Stars and Small Nebulae in the Small Magellanic CloudAn objective-prism survey of the Small Magellanic Cloud has beenperformed through an Hα + [N II] interference filter, using the0.90 m Curtis Schmidt telescope of Cerro Tololo. 1898 emission-lineobjects have been detected in the main body of this galaxy, almostquadrupling the number of those found, in the same region, by theprevious objective-prism surveys. Among these objects are newlydiscovered planetary nebulae, compact HII regions and late-type stars.Continuum intensity, as well as the shape and relative strength of theHα emission-line have been estimated; coordinates, cross-identifications for the listed objects and 2.25 arcmin square findingcharts for all the objects are provided. The neutral phases in the local interstellar medium at B > 10 and low velocities.Not Available Two new catalogues of Small Magellanic Cloud members coming soon.Not Available Accurate positions for SMC clustersPositions of 203 SMC clusters accurate to + or - 5 arcsec are reported.The astrometry method used is briefly described. Plans for futureMagellanic Cloud cluster astrometry are summarized. Spectral types of stars in the SMC associations NGC456, NGC460a, B and NGC465Spectral types of stars for an extended area (1200 sq arcmin) of theSMC, containing the associations NGC456, NGC460 a, b and NGC465 havebeen derived here. High-quality UJ and YJ film copies of objective prismplates taken with the 1.2-m UK Schmidt telescope were used. The mediumdispersion spectral (830 A/mm) were digitized with a PDSmicrodensitometer and spectra types of stars were obtained down to about16.5 mag. A computer interactive method of reduction has been developed,and the spectral types obtained are accurate to 0.3 spectral subtypes.Spectral classification for the low (2440 A/mm) dispersion spectra downto 18.5 mag was carried out visually using a binocular microscope. Thefrequency distributions of stars in the associations region, aftersubtracting the field stars, have revealed that only blue main sequencestars are their members. The Magellanic Clouds - Their evolution, structure and compositionRecent data related to the history of the Magellanic Clouds as galaxiesare described, and attempts to determine accurate distances to theMagellanic Clouds are discussed, with special attention given to thegeometry of the Magellanic Clouds and different methods of distancedeterminations. Consideration is given to the various star generationspresent in the Clouds (i.e., the oldest generation, of greater than 10Gyr; the intermediate-age generations, between 7 and 0.2 Gyr, and theyoungest generation, the formation of which started only about 50 Myrago) and to their occurrences in the LMC and SMC populations, as well asto the interstellar medium in the Magellanic Clouds. The structure ofthe Magellanic System, which comprises the Magellanic Clouds, theIntercloud Region, and the Magellanic Stream is described, withparticualr consideration given to the complex structure of the LMC andSMC and the kinematics of their populations. BVR photoelectric photometry of late-type stars and a compilation of other data in the Small Magellanic CloudThe basic data used in a discussion of the structure and morphology ofthe SMC Martin et al., (1989) are presented. New BVR photoelectric dataacquired at ESO, 88 SMC K-M type supergiants and three foreground Mstars; for all these stars, high-accuracy Coravel radial velocities hadbeen obtained. Taking into account all available data, a list of mean Vmagnitudes is obtained for 307 stars in the direction of the SMC withknown radial velocities. Also established is a list of mean weightedradial velocities on the IAU standard system for the 307 stars (amongwhich only two are probably foreground Galactic stars). The structure of the Small Magellanic CloudThe structure of the SMC is investigated using previous H-I data,accurate radial velocities of 307 young stars and 35 H-II regions, andhigh-spectral-resolution profiles of interstellar absorption lines. Itis found that 224 stars and 30 H-II regions of the main body of the SMCare associated with four H-I components, and that 54 of the objects arenot associated with H I. Two main complexes of gas, stars, and H-IIregions are found, one with a velocity of about -28 km/s and the otherwith a velocity of about +9 km/s. Most of the young stars are shown tolie within a depth smaller than 10 kpc, in agreement with recentMagellanic Cepheid data. Global photometric observations of 30 H II regions in the Small Magellanic CloudIntegrated photoelectric measurements of the equivalent width, theforbidden O-III/H-beta ratio, and the H-beta emission line flux weremade of 30 H-II regions in the SMC. The photometric system employedconsists of a narrow H-beta filter with Delta lambda = 30 A, a wideH-beta filter with Delta lambda = 150 A, and a forbidden O-III filtercentered at 5000 A. Calibration of the system is discussed. The presentdata have been compared with previous observations. Discovery of a low mass Be supergiant in the SMC.Not Available Photometric reddenings of stars in emission nebulae of the Magellanic CloudsVBLUW observations of stars in emission nebulae of the SMC and the LMCare discussed. The color indices, luminosities, and extinction in thecentral regions of the nebulae have been obtained. Stars such as N 159and N 160A are found to have extinctions AV of greater than1.5 mag. It is suggested that more luminous (and thus more massive)stars or groups of stars are located in the regions of highestextinction. Sequential star formation in the Magellanic CloudsJoint stellar and nebular studies were carried out for a few adjacentstellar associations in the Magellanic Clouds. The spread in ages of WRstars of different subtypes as deduced from their different environmentsis analyzed. A similar study is briefly sketched for S Dor type stars.It is shown how a starburst propagates in the interstellar medium at ascale of 100-300 pc in about 10 to the 7th yr for three regions of theMagellanic Clouds, using both new observational data and published ones.In view of the results provided by such detailed studies, several trapsin the methods were pointed out based on integrated properties of starclusters and their associated nebulae, or their brightest stars.Finally, the moderately old age found (from their environment) for S Dortype stars and their tendency to enter into multiple systems are pointedout.
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 Constellation: Tucana Right ascension: 01h14m00.00s Declination: -73Â°16'00.0" Apparent magnitude: 99.9

Catalogs and designations:
 Proper Names (Edit) NGC 2000.0 NGC 456 → Request more catalogs and designations from VizieR