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Ejecta Detection in Middle-Aged Large Magellanic Cloud Supernova Remnants 0548-70.4 and 0534-69.9
We have observed supernova remnants 0548-70.4 and 0534-69.9 in the LargeMagellanic Cloud (LMC) with the Chandra X-Ray Observatory and report onthe X-ray spectral analysis. Our images of 0548-70.4 and 0534-69.9 showbright central regions as well as brightened limbs. The X-ray spectrafrom the central regions exhibit enhanced metal abundances, insignificant contrast to limb spectra, which show abundances consistentwith the LMC interstellar medium (ISM). Considering the relatively oldages (~10,000 yr), these supernova remnants might be assumed to be inthe Sedov phase, in which the X-ray spectra would be dominated byswept-up ISM material. The detection of high abundances in these oldremnants is therefore surprising. Spectra from the limb regions wereanalyzed with Sedov models. The results were then used to account forblast wave emission seen in projection toward the central region andwere added to a plane-parallel shock model for the reverse shock in theejecta. We find elevated levels of iron, oxygen, magnesium, silicon, andsulfur in the bright central regions of each remnant. We introduce a newX-ray spectral shock model appropriate for heavy-element-dominatedplasmas, in which electrons liberated by successive ionizations dominatethe electron pool and modify the electron temperature profile. With thismodel, we find reverse-shock speeds of 420 km s-1 for0548-70.4, 500 km s-1 for the northeast central region of0534-69.9, and 360 km s-1 for its south central region. Theelemental abundances favor a Type Ia supernova origin for both 0548-70.4and 0534-69.9.
| 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.
| 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 Revised and Extended Catalog of Magellanic System Clusters, Associations, and Emission Nebulae. II. The Large Magellanic Cloud
A survey of extended objects in the Large Magellanic Cloud was carriedout on the ESO/SERC R and J Sky Survey Atlases, checking entries inprevious catalogs and searching for new objects. The census provided6659 objects including star clusters, emission-free associations, andobjects related to emission nebulae. Each of these classes containsthree subclasses with intermediate properties, which are used to infertotal populations. The survey includes cross identifications amongcatalogs, and we present 3246 new objects. We provide accuratepositions, classification, and homogeneous measurements of sizes andposition angles, as well as information on cluster pairs andhierarchical relation for superimposed objects. This unification andenlargement of catalogs is important for future searches of fainter andsmaller new objects. We discuss the angular and size distributions ofthe objects of the different classes. The angular distributions show twooff-centered systems with different inclinations, suggesting that theLMC disk is warped. The present catalog together with its previouscounterpart for the SMC and the inter-Cloud region provide a totalpopulation of 7847 extended objects in the Magellanic System. Theangular distribution of the ensemble reveals important clues on theinteraction between the LMC and SMC.
| Supernova Remnants in OB Associations
Abstract image available at:http://adsabs.harvard.edu/abs/1997AJ....113.1815C
| 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.
| 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.
| The detection of X-ray emission from the OB associations of the Large Magellanic Cloud
A systematic study of the X-ray properties of OB associations in theLarge Magellanic Cloud has been carried out using data from the EinsteinObservatory. An excess of young, X-ray-bright supernova remnants isfound in the vicinity of the associations. In addition, diffuse X-rayemission is detected from over two dozen other associations;luminosities in the 0.16-3.5 keV band range from 2 x 10 to the 34th (thedetection threshold) to 10 to the 36th ergs/s. For several of the moreluminous examples, it is shown that emission from interstellar bubblescreated by the OB stellar winds alone is insufficient to explain theemission. It is concluded that transient heating of the bubble cavitiesby recent supernovae may be required to explain the observed X-rays andthat such a scenario is consistent with the number of X-ray-brightassociations and the expected supernova rate from the young stars theycontain.
| X-rays from superbubbles in the Large Magellanic Cloud
Diffuse X-ray emission not associated with known supernova remnants(SNRs) are found in seven Large Magellanic Cloud H II complexesencompassing 10 OB associations: N44, N51D, N57A, N70, N154, N157 (30Dor), and N158. Their X-ray luminosities range from 7 x 10 to the 34thergs/s in N57A to 7 x 10 to the 36th ergs/s in 30 Dor. All, except 30Dor, have simple ring morphologies, indicating shell structures.Modeling these as superbubbles, it is found that the X-ray luminositiesexpected from their hot interiors fall an order of magnitude below theobserved values. SNRs close to the center of a superbubble add verylittle emission, but it is calculated that off-center SNRs hitting theionized shell could explain the observed emission.
| Vacuum ultraviolet images of the Large Magellanic Cloud
Linearized, absolutely calibrated VUV images of the LMC with aresolution of about 50 arcsec are presented. The images were made by asounding rocket payload in two bandpasses with effective wavelengths forhot stars near 1500 A and 1930 A. The flux in each bandpass is measuredfor the associations in the list of Lucke and Hodge (1970). The resultsare discussed and their relationship to the overall characteristics ofstar formation in the LMC are discussed. A simple model for propagatingstar formation in the LMC is presented whose results closely resemblethe distribution of associations revealed by the VUV images.
| Young stars and bubbles in the Large Megellanic Cloud
The generating mechanisms of bubbles are investigated on a galaxy-widescale for the Large Magellanic Cloud. Several formation processes forring-shaped and filamentary emission regions are considered, andformulas are given for the time dependence of the shell radius takingthe interaction of supernovas and stellar winds into account. Theparameters of associations and H II regions are compiled, reduced to ahomogeneous system, and presented. Correlations between associationparameters and emission region parameters are investigated. It is foundthat stellar content versus emission region diameter, H-alpha fluxversus FUV flux, star surface density versus H-alpha brightness, and FUVflux versus stellar content of blue stars all show correlations withcoefficients greater than 0.4. A diameter-age diagram for bubbleevolution is depicted in which the H II region evolution effect and thestellar wind effect are separated.
| Faint, nebulous filaments, 2000 PC diameter, around the 30 Doradus nebula
A 5h exposure of the Large Magellanic Cloud at H alpha + (N II) has beenprinted at high contrast and through a mask that filters out informationat low spatial frequencies. The consequences are that many filaments ofextremely faint nebulosity over a region, about 2000 pc diameter,surrounding the 30 Doradus nebula are revealed and their relationship tothe brighter central filaments demonstrated. All the nebulous ridges,the enclosed OB associations and H I ridges have been correlated.Spherical, or more probably, cylindrical, neutral and ionized shells areproposed to explain these phenomena.
| A survey of H2O masers in dense interstellar clouds
A high-sensitivity survey of 22-GHz H2O maser emission covering thedensest parts of 28 molecular clouds has been made with a 100-m radiotelescope. New maser sources were found in the W3, OMC 2, M17 N, S 106and NGC 7129 regions. The maser sources in OMC 2, M17 N and S 106 havesingle lines with the same radial velocity as the dense cloud where theyare embedded. They are at a small distance from regions where starformation is well under way and may correspond to very early stages ofstar formation triggered by nearby newly born stars. The masers in NGC7129 are probably of a different nature. The total absence of H2O masersin molecular clouds like the Rho Oph cloud, L 134, and several otherssuggests that star formation is not presently taking place in theseregions.
| A catalogue of stellar associations in the Large Magellanic Cloud.
Abstract image available at:http://adsabs.harvard.edu/abs/1970AJ.....75..171L
| A Catalogue of Clusters in The LMC
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