The Far Ultraviolet Spectroscopic Explorer Legacy in the Magellanic Clouds: An Online Stellar Sight Line Atlas
We present an atlas of stellar sight line data from the Far UltravioletSpectroscopic Explorer (FUSE) satellite for 287 stars in the MagellanicClouds, obtained from eight years of satellite operations. The intent ofour project is to make this rich ensemble data set accessible to a broadcommunity of researchers in a standardized format that will enable easyidentification of subsets of these data that are appropriate forpursuing specific science programs. We present the data in astandardized manner, showing key interstellar lines on a velocity scale,optical (MCELS) and infrared (Spitzer) sight line context images, andoverview plots of the spectral region containing the O VI??1032, 1038 doublet, and the entire 905-1187 Åspectral range observed with FUSE. Objects with multiple observationshave had their data summed to directly provide the highestsignal-to-noise ratio available. These data are accessible online as aHigh Level Science Product through the Multimission Archive at SpaceTelescope (MAST). In this article, we describe the data sets andprocessing, the atlas materials, and the MAST interface in detail, andalso provide examples of how to use these materials.
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A Quantitative Comparison of the Small Magellanic Cloud, Large Magellanic Cloud, and Milky Way Ultraviolet to Near-Infrared Extinction Curves
We present an exhaustive quantitative comparison of all the knownextinction curves in the Small and Large Magellanic Clouds (SMC and LMC)with our understanding of the general behavior of Milky Way extinctioncurves. The RV-dependent CCM relationship of Cardelli,Clayton, and Mathis and the sample of extinction curves used to derivethis relationship are used to describe the general behavior of Milky Wayextinction curves. The ultraviolet portion of the SMC and LMC extinctioncurves are derived from archival IUE data, except for one new SMCextinction curve, which was measured using Hubble Space Telescope SpaceTelescope Imaging Spectrograph observations. The optical extinctioncurves are derived from new (for the SMC) and literature UBVRIphotometry (for the LMC). The near-infrared extinction curves arecalculated mainly from 2MASS photometry supplemented with DENIS and newJHK photometry. For each extinction curve, we giveRV=A(V)/E(B-V) and N(H I) values that probe the same dustcolumn as the extinction curve. We compare the properties of the SMC andLMC extinction curves with the CCM relationship three different ways:each curve by itself, the behavior of extinction at differentwavelengths with RV, and the behavior of the extinction curveFitzpatrick and Massa fit parameters with RV. As has beenfound previously, we find that a small number of LMC extinction curvesare consistent with the CCM relationship, but the majority of the LMCand all the SMC curves do not follow the CCM relationship. For the firsttime, we find that the CCM relationship seems to form a bound on theproperties of all the LMC and SMC extinction curves. This resultstrengthens the picture dust extinction curves exhibit of a continuum ofproperties between those found in the Milky Way and the SMC bar.Tentative evidence based on the behavior of the extinction curves withdust-to-gas ratio suggests that the continuum of dust extinction curvesis possibly caused by the environmental stresses of nearby starformation activity.Partially based on observations made with the NASA/ESA Hubble SpaceTelescope, obtained at the Space Telescope Science Institute, which isoperated by the Association of Universities for Research in Astronomy,Inc., under NASA contract NAS 5-26555. These observations are associatedwith proposal 8198.
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A Reanalysis of the Ultraviolet Extinction from Interstellar Dust in the Large Magellanic Cloud
We have reanalyzed the Large Magellanic Cloud's (LMC) ultraviolet (UV)extinction using data from the IUE final archive. Our new analysis takesadvantage of the improved signal-to-noise ratio of the IUE NEWSIPSreduction, the exclusion of stars with very low reddening, the carefulselection of well-matched comparison stars, and an analysis of theeffects of Galactic foreground dust. Differences between the averageextinction curves of the 30 Dor region and the rest of the LMC arereduced compared with previous studies. We find that there is a group ofstars with very weak 2175 Å bumps that lie in or near the regionoccupied by the supergiant shell, LMC 2, on the southeast side of 30Dor. The average extinction curves inside and outside LMC 2 show a verysignificant difference in 2175 Å bump strength, but their far-UVextinctions are similar. While it is unclear whether or not theextinction outside the LMC 2 region can be fitted with the relation ofCardelli, Clayton, & Mathis (CCM), sight lines near LMC 2 cannot befitted with CCM because of their weak 2175 Å bumps. While theextinction properties seen in the LMC lie within the range of propertiesseen in the Galaxy, the correlations of UV extinction properties withenvironment seen in the Galaxy do not appear to hold in the LMC.
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Ultraviolet observations of stars in the Magellanic Clouds: a historical bridge from the Sun to R 136 and beyond.
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Ultraviolet Imaging Telescope Observations of the Magellanic Clouds
We present wide-field far-ultraviolet (FUV; 1300-1800 Å) images ofthe Large and Small Magellanic Clouds (LMC, SMC). These data wereobtained by the Ultraviolet Imaging Telescope (UIT) during the Astro-1(1990 December 1-10) and Astro-2 (1995 March 2-18) missions; the imagesprovide an extensive FUV mosaic of the SMC and contain numerous regionsin the LMC, covering a wide range of stellar densities and current starformation activity. A total of 47 LMC/Lucke-Hodge and 37 SMC/Hodge OBassociations are completely or partially included in the observedfields. FUV data can identify the hottest OB stars more easily than canoptical photometry, and these stars dominate the ionizing flux, which iscorrelated to the observed Hα flux of the associated H ii regions.Of the H ii regions in the catalog of Davies, Elliott, & Meaburn(DEM), the UIT fields completely or partially include 102 DEM regions inthe LMC and 74 DEM regions in the SMC. We present a catalog of FUVmagnitudes derived from point-spread function photometry for 37,333stars in the LMC (the UIT FUV magnitudes for 11,306 stars in the SMCwere presented recently by Cornett et al.), with a completeness limit ofm_UV ~ 15 mag and a detection limit of m_UV ~ 17.5. The averageuncertainty in the photometry is ~0.1 mag. The full catalog withastrometric positions, photometry, and other information is alsoavailable from publicly accessible astronomical data archives. We dividethe catalog into field stars and stars that are in DEM regions. Weanalyze each of these two sets of stars independently, comparing thecomposite UV luminosity function of our data with UV magnitudes derivedfrom stellar evolution and atmosphere models in order to derive theunderlying stellar formation parameters. We find a most probable initialmass function (IMF) slope for the LMC field stars of Gamma = -1.80 +/-0.09. The statistical significance of this single slope for the LMCfield stars is extremely high, though we also find some evidence for afield star IMF slope of Gamma ~ -1.4, roughly equal to the Salpeterslope. However, in the case of the stars in the DEM regions (the starsin all the regions were analyzed together as a single group), we findthree IMF slopes of roughly equal likelihood: Gamma = -1.0, -1.6, and-2.0. No typical age for the field stars is found in our data for timeperiods up to a continuous star formation age of 500 Myr, which is themaximum age consistent with the completeness limit magnitude of thecatalog's luminosity function. The best age for the collection ofcluster stars was found to be t_0 = 3.4 +/- 1.9 Myr; this is consistentwith the age expected for a collection of OB stars from many differentclusters.
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Molecular Hydrogen along Two Lines of Sight through the Large Magellanic Cloud
We have remeasured the H_2 column densities along lines of sight to theLarge Magellanic Cloud (LMC) using spectra taken by the HopkinsUltraviolet Telescope (HUT). Three lines of sight were analyzed usingthe pair method and previously determined Fitzpatrick & Massaextinction parameters to allow H_2 absorption models to be fitted.Substantial improvements over the values first reported by Clayton etal. were made for two of the three lines of sight. Comparisons betweenLMC and Galactic environments suggest that the factors which lead toextinction curve variations (e.g., metallicity or shocks) do not affectthe efficiency of H_2 formation on the surfaces of the dust grains:N_H_2/E(B-V) values are approximately the same in both galaxies despitelarge differences in N_H_I/E(B-V).
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The HIPPARCOS proper motion of the Magellanic Clouds
The proper motion of the Large (LMC) and Small (SMC) Magellanic Cloudusing data acquired with the Hipparcos satellite is presented. Hipparcosmeasured 36 stars in the LMC and 11 stars in the SMC. A correctlyweighted mean of the data yields the presently available most accuratevalues, mu_alpha cos(delta) = 1.94 +/- 0.29 mas/yr, mu_delta = - 0.14+/- 0.36 mas/yr for the LMC. For the SMC, mu_alpha cos(delta) = 1.23 +/-0.84 mas/yr, mu_delta = - 1.21 +/- 0.75 mas/yr is obtained, whereby careis taken to exclude likely tidal motions induced by the LMC. Bothgalaxies are moving approximately parallel to each other on the sky,with the Magellanic Stream trailing behind. The Hipparcos proper motionsare in agreement with previous measurements using PPM catalogue data byKroupa et al. (1994), and by Jones et al. (1994) using backgroundgalaxies in a far-outlying field of the LMC. For the LMC the Hipparcosdata suggest a weak rotation signal in a clockwise direction on the sky.Comparison of the Hipparcos proper motion with the proper motion of thefield used by Jones et al. (1994), which is about 7.3 kpc distant fromthe center of the LMC, also suggests clockwise rotation. Combining thethree independent measurements of the proper motion of the LMC and thetwo independent measurements of the proper motion of the SMC improvesthe estimate of the proper motion of the LMC and SMC. The correspondinggalactocentric space motion vectors are computed. Within theuncertainties, the LMC and SMC are found to be on parallel trajectories.Recent theoretical work concerning the origin of the Magellanic Systemis briefly reviewed, but a unique model of the Magellanic Stream, forthe origin of the Magellanic Clouds, and for the mass distribution inthe Galaxy cannot yet be decided upon. Future astrometric space missionsare necessary to significantly improve our present knowledge of thespace motion of the two most conspicuous galactic neighbours of theMilky Way.
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Transformations from Theoretical Hertzsprung-Russell Diagrams to Color-Magnitude Diagrams: Effective Temperatures, B-V Colors, and Bolometric Corrections
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJ...469..355F&db_key=AST
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Astro-2 Observations of Interstellar Dust and Gas in the Large Magellanic Cloud
This paper presents the first UV (1400-3200 A) polarimetry and far-UV(950-1200 A) spectrophotometry ever obtained for reddened stars in theLarge Magellanic Cloud (LMC). We derive the UV wavelength dependence ofinterstellar polarization down to 1400 A and that of extinction down tonear the Lyman limit. We also measure column densities of H_2_ alongthese lines of sight in the LMC. We have obtained these data with theHopkins Ultraviolet Telescope (HUT) and the Wisconsin Ultraviolet Photo-Polarimeter Experiment (WUPPE) using the Astro-2 Observatory, which flewon the Space Shuttle in 1995 March. The UV interstellar polarization inthe LMC shows a wavelength dependence similar to that seen in theGalaxy. The magnitude of the polarization in the UV lies on or above anextrapolation of the Serkowski curve. This is consistent with thewavelength dependence seen for low λ_max_ sight lines in theGalaxy. The far-UV extinction in the LMC continues to rise to 10.5micron^-1^, which confirms that large numbers of small grains arepresent. The measured column densities of H_2_ with respect to H I arelow compared to the Galaxy and track the previously measured lower dustabundance. The H_2_ abundance may be regulated by the amount of dustpresent. These new data will allow a comparison of how interstellar dustproperties vary in different galactic environments.
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On the motion of the Magellanic Clouds
We have measured the proper motion of the Large and Small MagellanicClouds using Magellanic Cloud stars in the PPM Catalogue, and obtainμ = 1.7+/-0.9 mas yr^-1^ for the LMC. Systematic uncertainties arediscussed. Bound and unbound orbits of the Magellanic Clouds around theGalaxy are consistent with our result. The various models of theMagellanic Stream and their predictions for the motion of the MagellanicClouds are discussed. The predictions by several authors for the sametype of model differ by up to 0.3 mas yr^-1^. All models proposed todate that assume the Magellanic Clouds to lead the Magellanic Streampredict a proper motion for the LMC of between 1.5 and 2.0 mas yr^-1^,the smallest value being a prediction for a Galaxy with no halo. Otherindependent measurements of the proper motion of the LMC are discussed.These lie between 1 and 1.5 mas yr^-1^. Future astrometry will have toallow measurement of the proper motion of the LMC with an uncertainty nolarger than one-tenth of a milliarcsecond per year in order to help todistinguish significantly between models of the halo of the Galaxy. Theproper motion of the LMC cannot by itself distinguish between models ofthe Magellanic Stream.
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A spectroscopic survey of B supergiants in the Large Magellanic Cloud
The results of a low-dispersion digital optical spectral survey of about100 B-type supergiants in the Large Magellanic Cloud are presented. TheMK spectral classification framework for B supergiants has beentransferred to the metal-weak LMC stars, and recommended classificationstandards have been designated. Variations among the metal linestrengths are examined. The most extreme variations are found for thenitrogen lines, for which a range of a factor of 3 or more may be seenin the equivalent widths within some spectral subclasses. It issuggested that these variations indicate a range of nitrogen surfaceabundances among the B supergiants, resulting from contamination of someof the stellar surfaces by processed material from the originalH-burning core.
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The spectrograms of Sanduleak -69.202 deg, precursor to supernova 1987A in the Large Magellanic Cloud
The classification spectrograms of Sk -69.202 deg from ESOobjective-prism plates are discussed and compared with data for sixother LMC supergiants of similar spectral types. It is found that thespectral type of Sk -69.202 deg must be in the range B0.7-B3. Theimplications of the observations for the properties of the SN 1987Aprecursor are examined, including the possibility of nitrogenenhancement.
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The properties of OB supergiants in the Large Magellanic Cloud. II - Spectral types and intrinsic colors
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1988ApJ...335..703F&db_key=AST
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"2-D Frutti" Spectra of B Supergiants in the Milky way and the LMC
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Supernova 1987A. A summary of the ESO Workshop held from 6 - 8 July 1987.
This has been a really exciting meeting! Not only have we heard manynew results, but it has also provided a fine example of how scienceshould be done. In particular we had vigorous interplay between theoryand observation, contributions from a variety of wavelength regionsand intense international collaboration.
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The distance to the LMC from UVBY beta photometry of B stars
The uvby beta photometry of nonsupergiant B stars in the LMC obtainedwith the 3.9-m Anglo-Australian telescope has been combined with earlierdata published on B supergiants to give a distance modulus of 18.3 + or- 0.2, corresponding to a distance of 46 kpc. This result is independentof the methods using Cepheids. It uses the same calibration of theluminosities of B stars as is used to determine the zero-point of theCepheid P/L/C relation in the Galaxy and provides an independent checkof that zero-point within the LMC.
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The properties of OB supergiants in the Large Magellanic Cloud. I - Energy distributions of 10 B supergiants
It is demonstrated here that line-blanketed, LTE plane-parallel modelatmosphere calculations provide excellent fits to the energydistributions from the ultraviolet through the visual ranges of Bsupergiants in the LMC. The models are computed using the atmosphereprogram of Kurucz (1979) but have been constructed with lower gravitiesthan were contained in Kurucz's model grid. The models are also shown tofit the ultraviolet through near-infrared continua of several lightlyreddened luminous Milky Way stars. Measurements of effectivetemperatures and gravities for 10 LMC B supergiants from model fits tothe continua are used to obtain estimates of the radii, luminosities,and masses of the stars. For supergiants earlier than type B2, theseparameters are reasonable when compared to the results of stellarevolution calculations. The results for the later B types, however,appear incompatible with evolution theory.
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The energy distributions of B supergiants in the Large Magellanic Cloud
It is shown that line-blanketed, LTE, plane-parallel model atmospherecalculations provide excellent fits to the ultraviolet-through-visualenergy distributions of B supergiants in the Large Magellanic Cloud. Themodels were computed using Kurucz's (1979) ATLAS atmosphere program, butwith lower gravities than were contained in Kurucz's published modelgrid. The ultraviolet continua of low gravity stars are found to besensitive to changes in temperature and gravity. Measurements of Teffand log g for ten LMC B supergiants from model atmosphere fits to theenergy distributions yield estimates of their radii, luminosities, andmasses. Model atmosphere fits suggest that the late B supergiants havesignificantly lower masses than the earlier B types of the sameluminosity, contrary to stellar evolution theory which predicts that Bsupergiants are in a post-core hydrogen burning phase and should evolvevery quickly and at essentially constant mass.
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A distance modulus of the LMC from UVBY beta photometry of B supergiants
Stromgren four-color and H-beta photometry has been obtained for 44 Bsupergiants in the Large Magellanic Cloud. As expected, nearly one-halfof them have beta indices which suggest emission at H-beta. From 24stars which appear to be free from this emission, thebeta/c0/M(v) calibration of Balona and Shobbrook (1984),applied with a correction to the beta index for the mean radial velocityof the LMC stars, indicates a distance modulus of 18.8 + or - 0.3.
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Interstellar extinction variations in the Large Magellanic Cloud
The properties of ultraviolet interstellar extinction in the LargeMagellanic Cloud (LMC) are investigated, with particular emphasis on theissue of regional variability. New IUE observations of reddened andstandard stars are combined with existing data from the IUE archives.The author finds essentially identical extinction properties toward 12stars located within about 500 pc projected distance of the core of the30 Dor nebula. The extinction curve toward these stars possesses a weak2175 Å extinction bump and a steep far-ultraviolet rise. Sixreddened stars located outside the 30 Dor region yield extinction curveswhich are significantly weaker in the far-ultraviolet than the 30 Dorcurve. These six curves all have similar far-ultraviolet strengths butshow a range of 2175 Å bump strengths. The results suggest that"typical" LMC extinction curves may not differ from typical Milky Waycurves as much as has been inferred from past studies which weredominated by stars near 30 Dor.
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Radial velocities from objective-prism plates in the direction of the Large Magellanic Cloud
A catalog is presented of 711 Large Magellanic Cloud (LMC) stars, withattention to the radial velocities of 418 of these. Also given are theradial velocities of 1127 galactic stars in the direction of the LMC, aswell as discussions of the precision of these measurements and of radialvelocity dispersion in different fields.
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Circumstellar absorption and intrinsic colours of massive stars
The reality of significant amounts of circumstellar obscuration formassive stars is discussed. At the same time, the question of thepossible incorrectness of currently adopted data for intrinsic colorindices of O stars is examined. The work is based primarily on recentdata for stars in the Large Magellanic Cloud and on new observationalresults for the galactic stellar aggregate surrounding HD 101205. Forthe high-luminosity stars in the Large Magellanic Cloud only marginaleffects of possible circumstellar obscuration may be traced, whereas forthe galactic stellar aggregate no such effects are noted. There is noconvincing overall indication that currently adopted intrinsic colorsfor O stars should be significantly in error.
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UBV photometry for supergiants of the Large Magellanic Cloud
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1975A&A....43..345B&db_key=AST
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Radial velocities from objective-prism plates in the direction of the Large Magellanic Cloud. List of 398 stars, LMC members. List of 1434 galactic stars, in the LMC direction
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1974A&AS...13..173F&db_key=AST
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Rotation et masse DU grand nuage de Magellan.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1973A&A....28..165P&db_key=AST
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Spectrographic and photometric observations of supergiants and foreground stars in the direction of the Large Magellanic Cloud
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972A&AS....6..249A&db_key=AST
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A deep objective-prism survey for Large Magellanic Cloud members
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Grand Nuage de Magellan. Liste des etoiles membres DU Grand Nuage de Magellan et liste d'etoiles galactiques
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Vitesses radiales dans la direction du Grand Nuage de Magellan
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INHABITED SKY
