Contents
Images
Upload your image
DSS Images Other Images
Related articles
Supernova Remnants in the Magellanic Clouds. VII. Infrared Emission from Supernova Remnants
We have used the instruments on the Spitzer Space Telescope to study theLarge Magellanic Cloud supernova remnants (SNRs) N11L, N44, N49, N206,N63A, and N157B. The two large SNRs N44 and N206 were not detected inany Spitzer IRAC or MIPS wave bands; the remainder were detected at oneor more wavelengths. In particular, the SNRs N49 and N63A each hadfeatures that were evident in all available IRAC and MIPS bands. Each ofthese two also displayed faint limb emission in the MIPS 24 μm bandonly. Spitzer IRS spectra obtained for the N49 SNR showed a number ofprominent lines, with little continuum contribution. We thereforesuggest that N49, and possibly N63A, are dominated by line emission,with thermal emission from hot dust being at most a secondary component.
| 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.
| Chandra Observation of the Magellanic Cloud Supernova Remnant 0454-67.2 in N9
A Chandra observation has defined the extent of the SNR 0454-67.2 in theLMC H II region N9. The remnant has dimension 2.3 arcmin×3.6 arcminand is elongated in the north-south direction. The brightest emissioncomes from a north-south central ridge that includes three brightpatches. There is good agreement between X-ray and [O III] and [S II]morphology. The remnant is old enough so that optical data give moreinformation about dynamics than do the X-ray data. The supernova (SN)energy release was >=5×1050 ergs, and the age is~3×104 yr. There are several unresolved sources nearby,but none are clearly associated with the remnant. The X-ray spectrum issoft and indicates enhanced Fe abundance in the central region,consistent with a Type Ia SN origin, but a Type II origin cannot beruled out.
| Supernova Remnants in the Magellanic Clouds. V. The Complex Interior Structure of the N206 Supernova Remnant
The N206 supernova remnant (SNR) in the Large Magellanic Cloud has longbeen considered a prototypical ``mixed morphology'' SNR. Recentobservations, however, have added a new twist to this familiar plot: anelongated, radially oriented radio feature seen in projection againstthe SNR face. Utilizing the high resolution and sensitivity availablewith the Hubble Space Telescope, Chandra, and XMM-Newton, we haveobtained optical emission line images and spatially resolved X-rayspectral maps for this intriguing SNR. Our findings present the SNRitself as a remnant in the middle to late stages of its evolution. X-rayemission associated with the radio linear feature strongly suggests itto be a pulsar wind nebula (PWN). A small X-ray knot is discovered atthe outer tip of this feature. The feature's elongated morphology andthe surrounding wedge-shaped X-ray enhancement strongly suggest a bowshock PWN structure.
| 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.
| The Supernova Remnant and Superbubble Components of the N206 Complex
Supernovae (SNe), through their diffuse supernova remnants (SNRs), areprimarily responsible for the injection of energy and heavy elementsinto the interstellar medium (ISM). The consequences of these injectionsare far-reaching. SNe provide most of the hot gas component of the ISM,and through collective inputs to structures such as superbubbles (SBs),can transfer hot gas into a galaxy halo. The energy and heavy elementsinfluence future generations of star formation in a galaxy and have aprofound effect on galaxy evolution.We have undertaken a large project to examine the dispersal of energyand heavy elements into a host galaxy by its population of SNRs and SBs,using the populations of therse objects in the Large and SmallMagellanic Clouds (LMC, SMC). As part of this study, we have examined ofthe neighboring N206 SNR (SNR B 0532-71.0) and N206 superbubble (DEM L221) at optical, X-ray and radio wavelengths.The N206 SNR was recently found to posess an elongated,radially-oriented radio feature. Utilizing the HST, Chandra, andXMM-Newton, we have obtained optical emission-line images and spatiallyresolved X-ray spectral maps for this SNR. Our findings imply the SNR isin the mid to late stages of its evolution. X-ray emission associatedwith the radio "linear feature" strongly suggests it to be a pulsar-windnebula (PWN). A small-diameter X-ray source is discovered at the outertip of this feature, which, with the feature's elongated morphology,suggests a bow-shock PWN structure.X-ray emission from the N206 superbubble had been detected with ROSAT.Using the higher sensitivity of XMM, we were able to obtain detailedspectral results for ths SB. We combine this information withground-based optical emission-line and radio HI data to form a completepicture of this SB and its possible enhancements of X-ray emission frominternal SNRs.
| Infrared Imaging of the Large Magellanic Cloud Star-forming Region Henize 206
Henize 206 is a region of star formation in the Large Magellanic Cloudof the approximate scale of the Orion belt and sword. Our Spitzer SpaceTelescope infrared images and Cerro Tololo Inter-American Observatory(CTIO) optical images show that the region is experiencing veryenergetic star formation. The radiation from young stars has excitedstrong polycyclic aromatic hydrocarbon (PAH) emission throughout Henize206, except on the side of the nebula with the prominent young supernovaremnant. As is also seen in early Spitzer observations of M81, starformation rates calculated from Hα for Henize 206 may miss thedeeply embedded young stars, compared with star formation ratescalculated from far infrared emission. For one of the highest surfacebrightness regions of Henize 206, we obtained snapshot exposures withthe Thermal-Region Camera Spectrograph on Gemini South to explore thecomplex structure. A few percent of the total flux from this brightestregion in Henize 206 emanates from infrared peaks of subparsec scale.
| Infrared Surface Brightness Fluctuations of Magellanic Star Clusters
We present surface brightness fluctuations (SBFs) in the near-IR for 191Magellanic star clusters available in the Second Incremental and All SkyData releases of the Two Micron All Sky Survey (2MASS) and compare themwith SBFs of Fornax Cluster galaxies and with predictions from stellarpopulation models as well. We also construct color-magnitude diagrams(CMDs) for these clusters using the 2MASS Point Source Catalog (PSC).Our goals are twofold. The first is to provide an empirical calibrationof near-IR SBFs, given that existing stellar population synthesis modelsare particularly discrepant in the near-IR. Second, whereas mostprevious SBF studies have focused on old, metal-rich populations, thisis the first application to a system with such a wide range of ages(~106 to more than 1010 yr, i.e., 4 orders ofmagnitude), at the same time that the clusters have a very narrow rangeof metallicities (Z~0.0006-0.01, i.e., 1 order of magnitude only). Sincestellar population synthesis models predict a more complex sensitivityof SBFs to metallicity and age in the near-IR than in the optical, thisanalysis offers a unique way of disentangling the effects of age andmetallicity. We find a satisfactory agreement between models and data.We also confirm that near-IR fluctuations and fluctuation colors aremostly driven by age in the Magellanic cluster populations and that inthis respect they constitute a sequence in which the Fornax Clustergalaxies fit adequately. Fluctuations are powered by red supergiantswith high-mass precursors in young populations and by intermediate-massstars populating the asymptotic giant branch in intermediate-agepopulations. For old populations, the trend with age of both fluctuationmagnitudes and colors can be explained straightforwardly by evolution inthe structure and morphology of the red giant branch. Moreover,fluctuation colors display a tendency to redden with age that can befitted by a straight line. For the star clusters only,(H-Ks)=(0.21+/-0.03)log(age)-(1.29+/-0.22) once galaxies areincluded, (H-Ks)=(0.20+/-0.02)log(age)-(1.25+/-0.16).Finally, we use for the first time a Poissonian approach to establishthe error bars of fluctuation measurements, instead of the customaryMonte Carlo simulations.This research has made use of the NASA/ IPAC Infrared Science Archive,which is operated by the Jet Propulsion Laboratory, California Instituteof Technology, under contract with the National Aeronautics and SpaceAdministration.
| OB stellar associations in the Large Magellanic Cloud: Survey of young stellar systems
The method developed by Gouliermis et al. (\cite{Gouliermis00}, PaperI), for the detection and classification of stellar systems in the LMC,was used for the identification of stellar associations and openclusters in the central area of the LMC. This method was applied on thestellar catalog produced from a scanned 1.2 m UK Schmidt Telescope Platein U with a field of view almost 6\fdg5 x 6\fdg5, centered on the Bar ofthis galaxy. The survey of the identified systems is presented herefollowed by the results of the investigation on their spatialdistribution and their structural parameters, as were estimatedaccording to our proposed methodology in Paper I. The detected openclusters and stellar associations show to form large filamentarystructures, which are often connected with the loci of HI shells. Thederived mean size of the stellar associations in this survey was foundto agree with the average size found previously by other authors, forstellar associations in different galaxies. This common size of about 80pc might represent a universal scale for the star formation process,whereas the parameter correlations of the detected loose systems supportthe distinction between open clusters and stellar associations.
| The relation between radio flux density and ionising ultra-violet flux for HII regions and supernova remnants in the Large Magellanic Cloud
We present a comparison between the Parkes radio surveys (Filipovic etal. 1995) and Vacuum Ultra-Violet (VUV) surveys (Smith et al. 1987) ofthe Large Magellanic Clouds (LMC). We have found 72 sources in common inthe LMC which are known HII regions (52) and supernova remnants (SNRs)(19). Some of these radio sources are associated with two or more UVstellar associations. A comparison of the radio flux densities andionising UV flux for HII regions shows a very good correlation, asexpected from theory. Many of the Magellanic Clouds (MCs) SNRs areembedded in HII regions, so there is also a relation between radio andUV which we attribute to the surrounding HII regions.
| 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.
| 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.
| RX J050736-6847.8: A Large Supernova Remnant around an X-Ray Binary in the Large Magellanic Cloud
RX J050736-6847.8 in the Large Magellanic Cloud (LMC) is an intriguingX-ray source consisting of a large ring (diameter~150 pc) of diffuseemission and a central compact source. It is projected in the vicinityof the superbubble N103 around the star cluster NGC 1850. RXJ050736-6847.8's ring of diffuse X-ray emission, offset from thesuperbubble N103, is not bounded by any optical shell structure, whileRX J050736-6847.8's central compact X-ray source is projected within thecluster HS122. We have analyzed archival ROSAT observations of RXJ050736-6847.8 to determine the physical properties of itsX-ray-emitting gas. The X-ray luminosity of the diffuse X-ray emissionis 5-6×1035 ergs s-1 in the 0.1-2.4 keVband, within the range for supernova remnants (SNRs). Assuming a shellgeometry with a fractional shell thickness (ΔR/R) of 0.05-0.2, wefind the density of the hot gas to be 0.05-0.09 cm-3 and ahot gas mass of ~820 Msolar. The physical properties of thisshell of hot gas are consistent with Sedov's solution for a~5×104 yr old SNR in a low-density (~0.015cm-3) medium formed by a supernova of an explosion energy of3×1051 ergs. The density is so low that no detectableoptical emission is expected. Therefore, we suggest that this ring ofX-ray emission originates in a SNR, the largest known in the LMC. Thelarge size, low density, and the regular X-ray morphology suggest thatthis SNR is located in the halo of the LMC; the small absorption columndensity further suggests that this SNR is on the near side of the LMChalo. The central compact source of RX J050736-6847.8 is probably anX-ray binary in the cluster HS122. The relationship between the compactsource and the diffuse ring is unknown.
| ROSAT HRI catalogue of X-ray sources in the LMC region
All 543 pointed observations of the ROSAT High Resolution Imager (HRI)with exposure times higher than 50 s and performed between 1990 and 1998in a field of 10°\ x 10°\ covering the Large Magellanic Cloud(LMC) were analyzed. A catalogue was produced containing 397 X-raysources with their properties measured by the HRI. The list wascross-correlated with the ROSAT Position Sensitive Propotional Counter(PSPC) source catalogue presented by Haberl & Pietsch (1999) inorder to obtain the hardness ratios for the X-ray sources detected byboth instruments. 138 HRI sources are contained in the PSPC catalogue,259 sources are new detections. The spatial resolution of the HRI washigher than that of the PSPC and the source position could be determinedwith errors mostly smaller than 15'' which are dominated by systematicattitude errors. After cross-correlating the source catalogue with theSIMBAD data base and the TYCHO catalogue 94 HRI sources were identifiedwith known objects based on their positional coincidence and X-rayproperties. Whenever more accurate coordinates were given in cataloguesor literature for identified sources, the X-ray coordinates werecorrected and the systematic error of the X-ray position was reduced.For other sources observed simultaneously with an identified source thecoordinates were improved as well. In total the X-ray position of 254sources could be newly determined. The catalogue contains 39 foregroundstars, 24 supernova remnants (SNRs), five supersoft sources (SSSs), nineX-ray binaries (XBs), and nine AGN well known from literature. Anothereight sources were identified with known candidates for these sourceclasses. Additional 21 HRI sources are suggested in the present work ascandidates for SNR, X-ray binary in the LMC, or background AGN becauseof their extent, hardness ratios, X-ray to optical flux ratio, or fluxvariability. Table 4 is only and Tables 1--3 are also available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html
| H I Shells in the Large Magellanic Cloud
A recent high-resolution H I survey of the Large Magellanic Cloud (LMC)shows that the structure of the neutral atomic interstellar gas isdominated by numerous shells and holes, as well as complex filamentaryand spiral-type structure. We present an up-to-date catalog of candidateH I supergiant and giant shells in the LMC. The candidates are visuallyselected from the H I data cube using selection and classificationcriteria that are described. Twenty-three supergiant shells, defined asthose regions whose extent is much larger than the H I scale height, arecataloged; 103 giant shells (radii less than the scale height of the H Igas) are cataloged. We further classify the H I shells into fivedifferent types, based on the comparison of the H I with theirassociated Hα emission. For this purpose, we obtained newwide-field Hα images of the LMC with a CCD camera mounted on a 16inch (0.41 m) telescope at Siding Spring Observatory. The pixel size of20" and the field of view of 12 deg are well matched to the H I survey.The size distribution of H I shells follows a crude power law,N(logR)~R-1.5. For constant energy input to the H I shellsand a constant shell creation rate, a shell luminosity spectrum of theform φ(L)~L-β, where β=1.75+/-0.2, isobtained. This agrees well with the observed H II region luminosityspectrum for the LMC of Kennicut, Edgar, & Hodge, which hasβ=1.75+/-0.15. H I shells containing H II regions and OBassociations seem to expand more rapidly than those without, providingdirect evidence for substantial input of mechanical energy from regionsof star formation.
| Ultraviolet Imaging Polarimetry of the Large Magellanic Cloud. II. Models
Motivated by new sounding-rocket wide-field polarimetric images of theLarge Magellanic Cloud (reported simultaneously by Cole et al.), we haveused a three-dimensional Monte Carlo radiation transfer code toinvestigate the escape of near-ultraviolet photons from young stellarassociations embedded within a disk of dusty material (i.e., a galaxy).As photons propagate through the disk, they may be scattered or absorbedby dust. Scattered photons are polarized and tracked until they escapethe dust layer, allowing them to be observed; absorbed photons heat thedust, which radiates isotropically in the far-infrared where the galaxyis optically thin. The code produces four output images: near-UV andfar-IR flux, and near-UV images in the linear Stokes parameters Q and U.From these images we construct simulated UV polarization maps of theLMC. We use these maps to place constraints on the star+dust geometry ofthe LMC and the optical properties of its dust grains. By tuning themodel input parameters to produce maps that match the observedpolarization maps, we derive information about the inclination of theLMC disk to the plane of the sky and about the scattering phase functiong. We compute a grid of models with i=28 deg, 36 deg, and 45 deg, andg=0.64, 0.70, 0.77, 0.83, and 0.90. The model that best reproduces theobserved polarization maps has i=36 deg+2-5 andg~0.7. Because of the low signal-to-noise in the data, we cannot placefirm constraints on the value of g. The highly inclined models do notmatch the observed centrosymmetric polarization patterns around brightOB associations or the distribution of polarization values. Our modelsapproximately reproduce the observed ultraviolet photopolarimetry of thewestern side of the LMC; however, the output images depend on many inputparameters and are nonunique. We discuss some of the limitations of themodels and outline future steps to be taken; our models make somepredictions regarding the polarization properties of diffuse lightacross the rest of the LMC.
| 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.
| 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.
| Spectroscopic binaries in the Large Magellanic Cloud.
Not Available
| A radio continuum study of the Magellanic Clouds. VII. Discrete radio sources in the Magellanic Clouds
We present a study of discrete radio sources in the Magellanic Clouds(MCs) using the latest large-scale radio surveys made with the Parkesradio telescope between 1.4 and 8.55 GHz. These surveys achieved highersensitivity then previous surveys done with the Parkes telescope and sothe number of discrete radio sources detected towards the MCs hasincreased by factor of five. Also, we have obtained improved positions,flux densities and radio spectral indices for all of these sources. Atotal of 483 sources towards the Large Magellanic Cloud (LMC) and 224towards the Small Magellanic Cloud (SMC) have been detected at at leastone radio frequency. Most of the MC's sources have been classified inone of three groups: SNRs, H Ii regions or background sources accordingto classification criteria established here. In total, 209 discreteradio sources in the LMC and the 37 sources in the SMC are classifiedhere to be either H Ii regions or SNRs. We investigate their luminosityfunctions as well as the statistics of background sources behind theMCs. Also, we examine the distribution of SNRs and H Ii regions in theMCs. Tables 5 and 6 are only available electronically at the CDS via ftp130.79.128.5 or via http://cdsweb.u-strasbg.fr/Abstract.html
| Extinction of H II regions in the Large Magellanic Cloud
The extinction properties of H II regions in the Large Magellanic Cloudare investigated using radio continuum data obtained from the MolongloObservatory Synthesis Telescope, digitized and calibrated H-alpha data,and published Balmer decrement measurements. The resultingextinction-color excess diagram suggests that (1) most H II regions inthe Magellanic Clouds have similar extinction properties to the Galacticones, (2) all imaginable gas/dust configurations are possible, and (3)the extinction of some highly reddened H II region cores originatesexternally in cocoon shells. The puzzle of different extinction-colorexcess ratios of Galactic and extragalactic H II regions is explained asbeing due to the different populations of observed samples rather thanany intrinsic differences. The extinction of the observed Galactic H IIregions produced by foreground dust overwhelms the internal extinction,while the situation in the observed extragalactic H II regions is justthe opposite.
| A radio continuum study of the Magellanic Clouds. VI. Discrete sources common to radio and X-ray surveys of the Magellanic Clouds
By comparing Parkes telescope radio surveys with the X-ray ROSAT All-SkySurvey (RASS) we have found 71 discrete sources of both radio and X-rayemission in the Large Magellanic Cloud (LMC). These 71 sources aremainly supernova remnants (SNRs) and SNR candidates (36), and backgroundsources (27). For six of the sources we have no proposed identificationand the other two are Hii regions. A source-intensity comparison of theradio and X-ray sources shows very little correlation, but we note thatthe strongest SNRs at both radio and X-ray frequencies are young SNRsfrom Population I. Six new LMC SNR candidates are proposed. From theradio flux density of the SNRs we have estimated the SNR birth rate tobe one every 100 (+/-20) yr and the star-formation rate (SFR) to be 0.7(+/-0.2) M_ȯyr(-1) . A similar comparison was undertaken for theSmall Magellanic Cloud (SMC), but instead of the RASS we used a rosterof pointed observations made with the ROSAT Position SensitiveProportional Counter (PSPC). This comparison resulted in 27 sources incommon between the Parkes radio and ROSAT PSPC surveys. Two new SMCsources are proposed for SNR candidates. The SMC SNR birth rate wasestimated to be one every 350 (+/-70) yr and the SFR was estimated to be0.15 (+/-0.05) M_ȯyr(-1) . Tables 2 and 3 are also availableelectronically at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or via http: //cdsweb.u-strasbg.fr/Abstract.html
| 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.
| H_2 and its relation to CO in the LMC and other magellanic irregular galaxies
H_2 column densities towards CO clouds in the LMC and SMC are estimatedfrom their far-infrared surface brightness and HI column density. Thenewly derived H_2 column densities imply N(H_{2)}/I(CO) conversionfactors (in units of 10(21) mol cm(-2) (K km s(-1) )(-1) ) X_LMC =1.3+/-0.2 and X_SMC = 12+/-2. LMC and SMC contain total (warm) H_2masses of 1.0+/-0.3 x 10(8) Msun and 0.75+/-0.25 x 10(8)Msun respectively. Local H_2/HI mass ratios similar to thosein LMC and SMC are found in the magellanic irregulars NGC 55, 1569,4214, 4449 and 6822 and in the extragalactic HII region complexes NGC604, 595 and 5461 in M 33 and M 101 respectively. In these HII regionsand in NGC 4449, we find X = 1-2; in NGC 55, 4214 and 6822 X = 3-6 againin units of 10(21) mol cm(-2) (K km s(-1) )(-1) . The post-starburstgalaxy NGC 1569 has a very high value similar to that of the SMC. TheCO-H_2 conversion factor X is found to depend on both the ambientradiation field intensity per nucleon {sigma _FIR/{N_H and metallicity[O]/[H]: log X ~ 0.9+/-0.1 logfrac {sigma _FIR{N_H - 3.5+/-0.2log([O])/([H]). Neglecting dependency on radiation field, a reasonableapproximation is also provided by log X ~ -2.7+/-0.3 log([O])/([H]).Milky Way values are consistent with these relations. This result isinterpreted as the consequence of selective photodissociation of COsubjected to high radiation field energy densities and poor(self)shielding in low-metallicity environments, and especially thepreferential destruction of diffuse CO in `interclump' gas. Althoughlocally H_2 may be the dominant ISM-component, the average global H_2/HImass ratio is 0.2+/-0.04 and the average H_2 gas mass fraction is0.12+/-0.02. Magellanic irregulars have warm molecular gas fractionsvery similar to those of our Galaxy, whereas other global properties(mass, luminosity, metallicity, CO luminosity) are very different.
| 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.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
Catalogs and designations:
|
