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Far Ultraviolet Spectroscopic Explorer Survey of Magellanic Cloud Supernova Remnants
We report the progress to date from an ongoing unbiased ultravioletsurvey of supernova remnants in the Magellanic Clouds using the FarUltraviolet Spectroscopic Explorer (FUSE) satellite. Earlier work withFUSE and other instruments has indicated that optical and/or X-raycharacteristics of supernova remnants are not always good predictors oftheir brightness in the ultraviolet. This survey is obtaining spectra ofa random large sample of Magellanic Cloud supernova remnants with abroad range of radio, optical, and X-ray properties. We proposed 39objects in the Large Magellanic Cloud and 11 objects from the SmallMagellanic Cloud, with a standard request of 10 ks per object using theFUSE 30" square aperture. To date, 39 objects have been observed in thesurvey (38 in the LMC and 1 in the SMC) and 15 have been detected, adetection rate of nearly 40%. Our survey has nearly tripled the numberof UV-detected SNRs in the Magellanic Clouds (from 8 to 22). Because ofthe diffuse source sensitivity of FUSE, upper limits on nondetectedobjects are quite sensitive in many cases, dependent on night observingfraction and whether stellar light contamination plays a role for agiven object. Estimated total luminosities in O VI, based simply onscaling the flux at the observed positions to an entire object, span abroad range from considerably brighter to many times fainter than theinferred soft X-ray luminosities, indicating that O VI can be animportant and largely unrecognized coolant in certain objects. Wecompare the optical and X-ray properties of the detected and nondetectedobjects but do not find a simple indicator for ultravioletdetectability. Nondetections may be due to clumpiness of the emission,high foreground extinction, slow shocks whose emission gets attenuatedby the Magellanic interstellar medium, or a combination of theseeffects. The characteristics of individual detected supernova remnantsare summarized in an Appendix.Based on observations made with the NASA-CNES-CSA Far UltravioletSpectroscopic Explorer. FUSE is operated for NASA by the Johns HopkinsUniversity under NASA contract NAS5-32985.
| The Σ - D relation for supernova remnants in nearby galaxies
This paper examines relations between the radio surface brightnessΣ and the diameter D (also known as Σ-D relations) for asample of extragalactic supernova remnants (SNRs) as constructed from acombination of published data and data from our own surveys. Our sampleof extragalactic SNRs is the largest ever devised for the purpose ofanalyzing Σ-D relations. The main results of this paper may besummarized as follows: (i) the empirical relations for SNRs in 10 of the11 nearby galaxies studied have the approximately trivial Σ∝D-2 form, therefore limiting their interpretation asphysically meaningful relations. In addition, these relations aresubject to selection effects rendering them even less useful. FurtherMonte Carlo simulations suggest that the effect of survey sensitivityhas the opposite effect of volume selection (e.g. Malmquist bias, avolume selection effect that shapes the Galactic sample) by tending toflatten the slopes toward a trivial relation. In this case, the trueslopes may be steeper than the observed slopes; (ii) compact M 82 SNRsappear to follow a uniquely different Σ-D relation in comparisonto the larger, older SNRs in the other 10 galaxies. Monte Carlosimulations suggest that the probability of this difference arising bychance is ≈1% to 10%, depending on what is assumed regarding theunderlying SNR population; (iii) three candidate hypernova remnants wereidentified in our sample of 11 nearby galaxies.
| On the nature of pre-main sequence candidate stars in the Large Magellanic Cloud
We investigate a sample of 18 Large Magellanic CloudHerbig Ae/Be candidate stars looking at their (1) spectral types (2)brightness variability mechanism and (3) near infra-red JHK emission. Wefind that the majority of the target stars have Hα emission, areof spectral type early- to mid-B and lack strong JHK excess emission.Their Balmer decrements are found to be similar to that of Galactic Bestars in general. Their erratic brightness variability is evaluated byusing the observed optical color excess and the color gradient from thelight curves and is subsequently interpreted as being due to variabledust obscuration or variable bf-ff emission from circumstellar ionizedgas. For approximately half of the target stars in our sample the typeof variability seems to be dissimilar to the mechanism involvingbound-free and free-free emission, but could be interpreted as caused byvariable dust obscuration, as we have proposed in earlier studies. It istherefore suggested that they are pre-main sequence objects, despite thefact that they nearly all lack thermal dust emission in the nearinfra-red; mid/far infra-red observations for these objects arewarranted. One star is observed to have JHK excess emission and aninspection of its 7.5 year MACHO light curve confirms its erraticphotometric behavior. The object displays deep photometric minima with aquasi-period of 191.3 days, as generally seen in the Galactic pre-mainsequence subgroup of the UX Orionis stars.Based on observations collected at ESO, La Silla.
| OH (1720 MHz) Maser Search toward the Large Magellanic Cloud
We have carried out a sensitive search for OH (1720 MHz) masers in theLarge Magellanic Cloud (LMC) toward five regions using the AustraliaTelescope Compact Array. Our source list includes the 30 Doradus regionand four supernova remnants (SNRs): N44, N49, N120, and N132D. Thesedata have a typical resolution of ~8" and rms noise levels of 5-10 mJybeam-1. We have detected OH (1720 MHz) masers in thenortheast part of 30 Doradus and toward the SNR N49. The OH (1720 MHz)maser emission in 30 Doradus is coincident with a cluster of young starsknown as ``knot 1'' and is almost certainly of the star formationvariety. Our spectral resolution (0.68 km s-1) isinsufficient to detect the Zeeman effect from the strongest (~320 mJybeam-1) of the 30 Doradus OH (1720 MHz) masers, leading to anupper limit to the field strength of 6 mG. The weak OH (1720 MHz) maseremission (35 mJy beam-1) detected toward the LMC SNR N49 islocated just west of a previously identified CO cloud and is indicativeof an interaction between the SNR and the molecular cloud. Although thestatistics are low, the detection rate seems consistent with that seenfor Galactic star-forming region and SNR type OH (1720 MHz) masers-bothof which are low.
| A Search for HAeBe stars in the bar of the Large Magellanic Cloud based on optical variability
We searched the EROS1 database consisting of 80 000 stars in the bar ofthe Large Magellanic Cloud for blue objects with irregular photometricbehavior similar to Galactic Herbig Ae/Be (HAeBe) stars. We found 14 newobjects in addition to the discovery of 7 HAeBe candidate stars found inour previous studies. Based on their light curve and colours we classifythese new objects also as EROS LMC HAeBe Candidates (ELHCs). The objectsare located in an area of enhanced 60 mu m emission, which indicates astar forming region. The stars are concentrated in three areas and themajority of the objects are clustered round the N 120 nebular complex.The light curves are interpreted with a simple model, involvingobscuration by an inhomogeneous orbiting circumstellar dust cloud as thedominant cause of the variability. We find that the dust orbiting thestars is at a radial distance in the order of 10 to a few 100 AUs. Mostof the objects are ``bluer-when-fainter''. This is attributed to thepresence of a (blue) scattering nebula with a size smaller than thepoint spread function of the photometric images. The stellar parametersare derived from the photometry. The luminosity of the stars is in therange of 3.4 < log (L/Lsolar) < 4.2 and the coloursindicate spectral types O or B. The stars are located in the HR-diagramabove the birthline for Galactic stars by about 1 dex in luminosity. Themethod used to detect the ELHCs stars on optical variability criteria isdiscussed. We show that our sample of HAeBe candidates in the EROS1field of view is complete up to V =~ 16.5 mfor the typicalamplitude and time scale of the ELHCs.
| 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
| A CO Survey of the LMC with NANTEN: III. Formation of Stellar Clusters and Evolution of Molecular Clouds
In order to elucidate star formation in the LMC, we made a completestudy of CO clouds with NANTEN. In the present paper, we compare 55giant molecular clouds (GMCs), whose physical quantities were welldetermined, with young objects, such as young stellar clusters and HIIregions. We find that the GMCs are actively forming stars and clusters;23 and 40 are found to be associated with the clusters and the HIIregions, respectively. The clusters associated with the GMCs aresignificantly young; ~ 85% of them are younger than ~ 10 Myr. Inaddition, compact groups of the young clusters are often found at thepeak position of the GMCs, e.g., N 159 and N 44, while much loosergroups are away from the GMCs. This suggests that the clusters areformed in groups and disperse as they become old. The distributions ofthe CO, [CII], and UV indicate that the GMCs are likely to be rapidlydissipated within several Myr due to UV photons from the clusters. Wealso estimate the evolutionary time scale of the GMCs; they form starsin a few Myr after their birth, and form clusters during the next fewMyr, and are dissipated in the subsequent few Myr.
| Large-Scale Diffuse X-Ray Emission from the Large Magellanic Cloud
X-ray mosaics of the Large Magellanic Cloud (LMC) taken with the ROSATPosition Sensitive Proportional Counter (PSPC) have revealed extensivediffuse X-ray emission, indicative of hot >=106 K gasassociated with this irregular galaxy on scales from ~10 to >=1000pc. We have selected regions of large-scale (d>=600 pc) diffuse X-rayemission, such as supergiant shells, the LMC Spur, and the LMC Bar, andexamined the physical conditions of the hot gas associated with them. Wefind that for these objects the plasma temperatures range from kT~0.15to 0.60 keV and the derived electron densities range fromne~0.005 to 0.03 cm-3. Furthermore, we haveexamined the fraction of diffuse X-ray emission from the LMC andcompared it to the total X-ray emission. We find that discrete sourcessuch as X-ray binaries and supernova remnants account for ~41% and ~21%of the X-ray emission from the LMC, respectively. In contrast, diffuseX-ray emission from the field and from supergiant shells account for~30% and ~6% of the total X-ray emission, respectively.
| Circumstellar masers in the Magellanic Clouds
Results are presented of a search for 22 GHz H_2O616->523, 43 GHz SiOv=1(J=1->0),86 GHz SiOv=1(J=2->1) and 129 GHzSiOv=1(J=3->2) maser emission from bright IRAS pointsources in the Small and Large Magellanic Clouds - mostly circumstellarenvelopes around obscured red supergiants and Asymptotic Giant Branchstars (OH/IR stars). The aim of this effort was to test whether thekinematics of the mass loss from these stars depends on metallicity.H_2O maser emission was detected in the red supergiants IRAS 04553-6825and IRAS 05280-6910, and tentatively in the luminous IR object IRAS05216-6753 and the AGB star IRAS 05329-6708, all in the LMC.SiOv=1(J=2->1) maser emission was detected in IRAS04553-6825. The double-peaked H_2O maser line profiles of IRAS04553-6825 and IRAS 05280-6910, in combination with the OH (and SiO)maser line profiles, yield the acceleration of the outflows from thesestars. The outflow velocity increases between the H_2O masing zone nearthe dust-formation region and the more distant OH masing zone from v ~18 to 26 km s-1 for IRAS 04553-6825 and from v ~ 6 to 17 kms-1 for IRAS 05280-6910. The total sample of LMC targets isanalysed in comparison with circumstellar masers in the Galactic Centre.The photon fluxes of circumstellar masers in the LMC are found to bevery similar to those in the Galactic Centre. The expansion velocitiesin the LMC appear to be ~ 20% lower than for similarly bright OH masersin the Galactic Centre, but the data are still consistent with nodifference in expansion velocity. OH/IR stars in the LMC appear to haveslower accelerating envelopes than OH/IR stars in the Galactic Centre.The masers in the LMC have blue-asymmetric emission profiles. This maybe due to the amplification of stellar and/or free-free radiation,rather than the amplification of dust emission, and may be morepronounced in low metallicity envelopes. The SiO maser strengthincreases with the photometric amplitude at 2.2 mu m but is independentof the photometric amplitude at 10 mu m. This suggests a strongconnection between shocks in the dust-free SiO masing zone and the dustformation process. The LMC masers obey the same trend as the GalacticCentre masers. Appendices describe H_2O maser emission from themoderately mass-losing AGB star R Dor in the Milky Way, optical echellespectroscopy of IRAS 04553-6825, and the properties of circumstellarmasers in the Galactic Centre.
| 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.
| A ROSAT PSPC catalogue of X-ray sources in the LMC region
We analyzed more than 200 ROSAT PSPC observations in a 10 by 10 degreefield centered on the Large Magellanic Cloud (LMC) and performed between1990 and 1994 to derive a catalogue of X-ray sources. The list contains758 sources with their X-ray properties. From cross-correlations of thePSPC catalogue with the SIMBAD data base and literature searches we givelikely identifications for 144 X-ray sources based on positionalcoincidence, but taking into account X-ray properties like hardnessratios and source extent. 46 known sources are associated with supernovaremnants (SNRs) and candidates in the LMC, most of them already detectedby previous X-ray missions. Including the new candidates from\cite[Haberl & Pietsch (1999)]{HP99} based on variability studies ofthe sources in our PSPC catalogue, the number of X-ray binaries in theLMC increased to 17 and that of the supersoft sources (SSSs) to 9. Theremaining ~ 50% of the identified sources comprise mainly foregroundstars (up to 57) and background extragalactic objects (up to 15). Theoften distinguished X-ray properties of the different source types wereused for a first classification of new, unknown X-ray sources. Eight newPSPC sources are classified as SNRs from their hardness ratios and onepromising new SNR candidate with extended X-ray emission is foundfurther north than all known SNRs. Three soft X-ray sources havehardness ratios compatible to those of the known SSSs. A selection onhardness ratios and X-ray to optical flux ratio further suggests 27foreground stars and 3 AGN.
| Supernova Remnants in the Magellanic Clouds. III. an X-Ray Atlas of Large Magellanic Cloud Supernova Remnants
We have used archival ROSAT data to present X-ray images of 31 supernovaremnants (SNRs) in the Large Magellanic Cloud (LMC). We have classifiedthese remnants according to their X-ray morphologies, into thecategories of shell-type, diffuse face, centrally brightened,point-source-dominated, and irregular. We suggest possible causes of theX-ray emission for each category and for individual features of some ofthe SNRs.
| 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
| Supernova Remnants in the Magellanic Clouds. II. Supernova Remnant Breakouts from N11L and N86
The evolution of a supernova remnant (SNR) is heavily influenced by theinterstellar conditions surrounding the remnant. This is particularlytrue in cases where the SNR is breaking out into a low-density area inthe surrounding medium. We examine two promising candidates for thestudy of SNR breakouts in the Large Magellanic Cloud (LMC): N11L andN86. The remnant N11L has a filamentary extension that interrupts theshell; to the north of this extension, we find a region of diffuse radioand X-ray emission that shows only faint filaments in optical images.The discontinuous distribution of velocities in the shell material andthe apparent flattening of the radio spectral index in the outflowregion suggest substantial turbulence in the outflowing material andclumpiness in the surrounding interstellar medium (ISM). N86, on theother hand, shows a large breakout to the north, as well as severalsmaller possible outflows around the shell. We find that the northernbreakout has a well-defined spherical expansion pattern, faint diffuseX-ray emission, and a highly filamentary optical structure. Our velocitydata indicate that material breaking out to the north is expanding at amaximum of 100 km s^-1. The consequences of these breakouts on theparent remnants are discussed: N11L appears to have a lower thermalenergy, by an order of magnitude, than other LMC remnants used forcomparison. N86, on the other hand, shows a thermal energy fairlysimilar to the comparison SNRs, perhaps due to a more gradual loss ofhot gas. The implications of the breakout structures for the surroundingmedium are also discussed. The breakout in N11L coincides with apossible low-density cavity, which is enclosed in a shell structure onthe western edge of the N11 H II complex. The less dense shell of N86and the more distributed pattern of the breakouts suggest a relativelylow density ISM with substantial local density variations.
| Magellanic Cloud X-Ray Sources. III. Completion of a ROSAT Survey
This paper concludes a series of three papers presenting ROSAT HighResolution Imager (HRI) observations of unidentified Einstein andserendipitous ROSAT X-ray sources in the direction of the MagellanicClouds. Accurate positions and fluxes have been measured for thesesources. Optical photometry and spectroscopy were obtained to search foridentifications in order to determine the physical nature of thesesources. The present paper includes new data for 24 objects;identifications are given or confirmed for 30 sources. For six sources,optical finding charts showing the X-ray positions are provided. Theresults from this program are summarized, showing that the populationsof luminous X-ray sources in the Magellanic Clouds are quite differentfrom those in the Galaxy.
| Marseille Observatory H-alpha survey of the southern Galactic Plane and Magellanic Clouds
The ionized gas regions, which are the main tracers of the spiral arms,can be used for the study and determination of the spiral structure ofour Galaxy. Towards this goal, the Marseille Observatory elaborated anddeveloped an instrument, using a scanning Fabry-Perot interferometer,particularly suited for the observation of extended objects. The surveyof the southern Galactic plane then started at the beginning of 1990.The major instrumental aim is to obtain the spectral information, andtherefore the ionized gas kinematics, in each pixel of the observedfields. Already 300 fields of 38'X38' have been observed in H-alpha witha spatial resolution of 9" X 9", covering almost the entire fourthquadrant of the Galactic plane, detecting numerous discrete HII regionsand the diffuse emission which is widely distributed. Also, theMagellanic Clouds are studied using the same instrument.
| 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.
| Five Mature Supernova Remnants in the Large Magellanic Cloud
Radio observations of the extended supernova remnants (SNRs) N23:SNR,N120:SNR, 0525-660, N49, and N44:shell 3 in the Large Magellanic Cloudshow a variety of structures and little difference from shell SNRs inthe Milky Way. N23:SNR and N120:SNR have very regular outlines, but theshells are much brighter on the sides toward the most prominent parts oftheir associated H ii region complexes, probably reflecting densitygradients in the surroundings. N23:SNR has a mixed magnetic fieldorientation and a mean magnetic field strength of 15 muG. Its magneticenergy is about 4 times less than the relativistic electron energy. SNR0525-660 appears to be isolated in the northern region of the LMC; ithas a partial shell of thin filaments and some bright, patchy emissionacross the face of the remnant. N49, one of the brightest SNRs in theLMC, shows the strongest polarized emission in the west, where the totalintensity is very weak, probably as a result of high magnetic fieldorganization. N44:shell 3, on the northeastern edge of a very large H iiregion complex, is definitely confirmed as an SNR but has a differentcentral position and outline at radio wavelengths than it does at X-raywavelengths.
| Supernova Remnants in OB Associations
Abstract image available at:http://adsabs.harvard.edu/abs/1997AJ....113.1815C
| High velocity motions inside the HII region N 103 of the Large Magellanic Cloud.
We have observed the HII region N 103 of the Large Magellanic Cloud witha scanning Fabry-Perot interferometer at Hα and [OIII]5007wavelengths. The kinematics of this field shows high velocity motions.We discuss their origin: Supernova explosion or particularly strongstellar winds. By calculating the energy input inside the gas, we showthat it is unlikely that the high velocity motions are due to thestellar winds of the embbeded stars. Then the nebula N 103 is linked totwo supernova remnants of different ages. The oldest one can berepresented by a bubble, 152pc wide, seen projected against the HIIregion, and probably lying at the edge of the HII region. The excitingstars of the nebula are actually members of the LMC cluster NGC 1850B;they provide a photon flux large enough to ionize the quiet part of thegas.
| 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.
| 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.
| The exciting star of the small bubble N 120A in the Large Magellanic Cloud
UV characteristics of the star BI 141 show that it is the exciting starof the nebula N 120A of the LMC. We determine its UV spectralclassification as O_9.5_I and we derive the terminal velocity andmass-loss rate of its stellar wind, in agreement with the usual valuesfound for galactic supergiants of the same spectral type. The energeticbalance between the power of the stellar wind and the measured energeticinput into the surrounding gas shows that the wind is largely thedominant factor for driving the bubble. The best model for the sustainedbubble is the model with conservation of energy, (nonradiative shockedstellar winds). The discrepancy between the visible spectralclassification B_3_I and the UV classification opens the questions ofeither the multiplicity or the variability of BI 141, and of its stellarwind.
| Kinematics of supernova remnants in the Magellanic Clouds.
Abstract image available at:http://adsabs.harvard.edu/abs/1993RMxAA..27...41R
| 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.
| The Supernova Remnant N:120 in the Large Magellanic Cloud
The detailed radial velocity field of the SNR N 120, in the LMC, hasbeen obtained for the Hα line with a spatial resolution of 2.6"over a 3' x 3' field. The profiles of the radial velocities presentcomplex splittings and simultaneously large broadenings. The gaseouscomponents identified along the line of sight, belong to the nebularcomplex N 120 and to the SNR. They are carefully separated, and thus thetrue Hα morphology of the SNR is obtained. The peculiar velocityfield of the SNR indicates an interaction with the neighbouring nebula,and departures from spherical geometry which can be due to small scaleinhomogeneities of the interstellar medium where the supernova exploded.The expansion velocity of the clumps is 100 km s^-1^ and the preshockdensity evaluated for the clumps is 10atcm^-3^. The large broadenings ofthe split velocity components of the SNR can reach 90 km s^-1^,revealing high internal motions. They indicate the presence of secondaryshocks induced inside the clumps by a fast blast wave probablyresponsible also for the X-ray emission. The broadenings and the radialvelocities appear to present some correlation suggesting that the shocksinduced inside the cloudlets have a direction related to the directionof the blast wave velocity.
| 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.
| N120 in the LMC - A sample of nebulae of different types
The present kinematic data and H-alpha surface brightness observationsfor the N120 nebular bubblelike complex of the LMC indicate that thiscomplex is composed of several smaller nebulae having various originsthat form a ring, rather than being a random superposition along theline-of-sight. Violent motions are noted at the periphery of thecomplex; this differs from the case of a normal 'ring-shaped nebula' inradial expansion, and suggests star formation occurring at theboundaries of the ring several million years ago. The significance ofthe high density medium in the giant nebulae of external galaxies isnoted.
| Flux densities at 8400 MHz for a large sample of radio sources
This paper presents 8400-MHz flux densities for 1194 southern radiosources. The sources were selected from the Parkes 2700-MHz Survey toinclude all those stronger than 0.5 Jy at that survey's findingfrequency of 2700 MHz. The new fluxes have an accuracy of about 8percent, corresponding to 0.05 Jy for a typical source. It isanticipated that the data will be useful in defining the high-frequencyradio spectra of many sources as well as in pinpointing objects withwhich to improve the southern, astrometric absolute reference frame.
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