A Radio and Optical Polarization Study of the Magnetic Field in the Small Magellanic Cloud
We present a study of the magnetic field of the Small Magellanic Cloud(SMC), carried out using radio Faraday rotation and optical starlightpolarization data. Consistent negative rotation measures (RMs) acrossthe SMC indicate that the line-of-sight magnetic field is directeduniformly away from us with a strength 0.19+/-0.06 μG. Applying theChandrasekhar-Fermi method to starlight polarization data yields anordered magnetic field in the plane of the sky of strength 1.6+/-0.4μG oriented at a position angle 4deg+/-12deg,measured counterclockwise from the great circle on the sky joining theSMC to the Large Magellanic Cloud (LMC). We construct athree-dimensional magnetic field model of the SMC, under the assumptionthat the RMs and starlight polarization probe the same underlyinglarge-scale field. The vector defining the overall orientation of theSMC magnetic field shows a potential alignment with the vector joiningthe center of the SMC to the center of the LMC, suggesting thepossibility of a ``pan-Magellanic'' magnetic field. A cosmic-ray-drivendynamo is the most viable explanation of the observed field geometry,but has difficulties accounting for the observed unidirectional fieldlines. A study of Faraday rotation through the Magellanic Bridge isneeded to further test the pan-Magellanic field hypothesis.
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Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
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Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
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An exploratory non-LTE analysis of B-type supergiants in the Small Magellanic Cloud
A preliminary differential non-LTE model atmosphere analysis of moderateresolution (R ~ 5 000) and signal-to-noise ratio spectra of 48 SmallMagellanic Cloud B-type supergiants is presented. Standard techniquesare adopted, viz. plane-parallel geometry and radiative and hydrostaticequilibrium. Spectroscopic atmospheric parameters (T_eff, log g andv_turb), luminosities and chemical abundances (He, C, N, O, Mg and Si)are estimated. These are compared with those deduced for a comparablesample of Galactic supergiants. The SMC targets appear to have similaratmospheric parameters, luminosities and helium abundances to theGalactic sample. Their magnesium and silicon underabundances arecompatible with those found for main sequence SMC objects and there isno evidence for any large variation in their oxygen abundances. Bycontrast both their carbon and nitrogen lines strengths are inconsistentwith single abundances, while their nitrogen to carbon abundance ratiosappear to vary by at least as much and probably more than that found inthe Galactic sample.
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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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Revised spectral types for 64 B-supergiants in the Small Magellanic Cloud: metallicity effects.
The problem of the classification of metal poor stars, such as occur inthe Small Magellanic Cloud (SMC), is discussed with reference to theapplicability of the MK system in such an environment. An alternativemethod is presented here and applied to B-type supergiants in the SMC. Alocal reference system is first devised and then a transformation to MKspectral types is determined by comparing the trends of metal linestrengths in these two systems. For the determination of the luminosityclass, we emphasize the need to use the hydrogen Balmer line strengthsindependently of metal line-strength considerations. This method is usedto determine new spectral types for 64 supergiants in the SMC, 75% ofthe sample requiring classifications different from previous findings.These new types result in much improved line strength - spectral typecorrelations for He, C, N, O, Mg and Si. Corresponding changes in thedistribution of these stars in the Hertzsprung-Russell diagram of theSMC reveal more clearly than before the existence of a ridge which maybe the SMC analogue of a similar feature found for the LMC byFitzpatrick & Garmany (1990ApJ...363..119F). The group of veryluminous supergiants lying above this ridge includes the LBV AV415(R40), a property which this object has in common with LBVs in the LargeMagellanic Cloud. Also, for the first time, clear examples of BN/BCsupergiants are found in the SMC.
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Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
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Positional reference stars in the Magellanic Clouds
The equatorial coordinates are determined of 926 stars (mainly ofgalactic origin) in the direction of the Magellanic Clouds at the meanepoch T = 1978.4 with an overall accuracy characterized by the meanvalues of the O-C coordinates, Sa = 0.35 arcsec and Sd = 0.38 arcsec,calculated from the coordinates of the Perth reference stars. Thesevalues are larger than the accuracy expected for primary standard stars.They allow the new positions to be considered as those of reliablesecondary standard stars. The published positions correspond to anunquestionable improvement of the quality of the coordinates provided inthe current catalogs. This study represents an 'astrometric step' in thestarting of a 'Durchmusterung' of the Magellanic Clouds organized by deBoer (1988, 1989).
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Structure of the interstellar medium in the Magellanic Clouds
Using optical and UV observations, the internal gas structure ofMagellanic Clouds (MCs) was examined for clues to the recent evolutionof the Magellanic System and further signs of this collision event.Results indicate that the intermediate velocity clouds (IVCs) havedifferent origins. Thus, the '60-km/s' IVC is clearly of Galacticorigin. The '130-km/s' IVC is probably also Galactic and is not directlyassociated with the MCs. The '170 km/s' IVC is quite clearly associatedwith the LMC and seems to be the front of the LMC. The overall gasstructure in the MCs indicates that there is a distance-velocityassociation except in two regions: one to the south-west of the SMC (andis enigmatic), and the other to the south of 30 Doradus and appears tobe smoothly linked with the H I bridge, indicating that both featureshave a common overall cause such as the recent tidal collision.
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BVR photoelectric photometry of late-type stars and a compilation of other data in the Small Magellanic Cloud
The basic data used in a discussion of the structure and morphology ofthe SMC Martin et al., (1989) are presented. New BVR photoelectric dataacquired at ESO, 88 SMC K-M type supergiants and three foreground Mstars; for all these stars, high-accuracy Coravel radial velocities hadbeen obtained. Taking into account all available data, a list of mean Vmagnitudes is obtained for 307 stars in the direction of the SMC withknown radial velocities. Also established is a list of mean weightedradial velocities on the IAU standard system for the 307 stars (amongwhich only two are probably foreground Galactic stars).
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The structure of the Small Magellanic Cloud
The structure of the SMC is investigated using previous H-I data,accurate radial velocities of 307 young stars and 35 H-II regions, andhigh-spectral-resolution profiles of interstellar absorption lines. Itis found that 224 stars and 30 H-II regions of the main body of the SMCare associated with four H-I components, and that 54 of the objects arenot associated with H I. Two main complexes of gas, stars, and H-IIregions are found, one with a velocity of about -28 km/s and the otherwith a velocity of about +9 km/s. Most of the young stars are shown tolie within a depth smaller than 10 kpc, in agreement with recentMagellanic Cepheid data.
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Effective temperatures and radii of Small Magellanic Cloud supergiants
The effective temperatures and radii of Small Magellanic Cloudsupergiants are found by comparison with models. The methods usedparallel those used previously by the authors for the Large Cloud and byUnderhill and co-workers for the Galaxy. No significant difference isfound among these galaxies in this respect. A new analysis of the SMCextinction law is presented.
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Studies of massive stars in the Magellanic Clouds. II - New spectral classification of OB stars in the SMC
Abstract image available at:http://adsabs.harvard.edu/abs/1987AJ.....93.1070G
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Radial velocities of southern stars obtained with the photoelectric scanner CORAVEL. VI - 233 F to M type stars in and near the Small Magellanic Cloud - Comparison with 80 spectrographic radial velocities of O to K type stars in this galaxy
Abstract image available at:http://adsabs.harvard.edu/abs/1987A&AS...67..423M
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Gas in and toward the Magellanic Clouds
Attention is given to the Ca II K absorption spectra of 48 early-typesupergiants in the SMC and LMC, with a view to the Clouds' possiblefragmentary nature and the distance of the gas responsible for theabsorption lines at 60 and 120 km/sec. The comparison of the spectraobtained with H I measurements toward the Clouds indicates that in bothClouds, the velocity components in the neutral hydrogen distribution lieat different distances along the line of sight. Good agreement is foundbetween the radial velocity shown in absorbing material and the radialvelocity spread predicted by Murai and Fujimoto's (1980) dynamical modelof the formation of the Magellanic Stream by tidal stripping. It isspeculated that both the SMC and LMC are extended and fragmented alongthe line of sight.
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The brightest stars as extragalactic distance indicators
The luminosities of the brightest blue and red supergiants werecalibrated by the spectra and photometry of such stars in six LocalGroup galaxies. It is found that the brightest blue supergiants are allA type supergiants, their luminosities depending strongly on theluminosity of the parent galaxy. The same relationship obtains for themost luminous (bolometric) stars in the galaxies. It is also found thatthere is a tight upper limit to the visual luminosities of the Msupergiants at -8.0 + or - 0.2 mag in spiral and irregular type galaxiescovering almost 6 mag of galactic luminosity from -20.5 to -14.8 mag. Itis concluded that the M supergiants are excellent extragalactic distanceindicators for spiral and Magellanic type irregular galaxies andprobably also for the less luminous dwarf irregular galaxies.
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Studies of luminous stars in nearby galaxies. VIII - The Small Magellanic Cloud
The spectra, colors, and positions on the H-R diagrams of the SmallMagellanic (SMC) supergiants of all spectral types are examined andcompared with corresponding data for supergiant populations in the LMCand Milky Way for clues to the role of chemical composition (i.e., lowmetallicity) on their evolution. A comparison of the observed luminosityfunction shows that while the solar neighborhood and the LMC areessentially the same, the SMC is significantly different, especially atthe upper end. These differences are not due to chemical-compositionvariations. The relative numbers of supergiants of differentluminosities vary most closely with the mass of the galaxy. The blue tored supergiant ratio in the SMC confirms the trends observed in theGalaxy and LMC, and is probably affected by chemical abundancedifferences, especially in the lower luminosity intervals. In addition,it is found that a group of supergiants in the SMC, with spectral typesB8-A5, have anomalous colors and hydrogen lines too strong for theirluminosities.
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Equivalent width measurements in galactic supergiant and in Small Magellanic Cloud star spectra
Measurements of equivalent width are made in spectra of 40 galacticsupergiants and 21 Small Magellanic Cloud stars. These measurementsconfirm the results of spectral classification in the SMC (Dubois etal., 1977) and show a general weakness of the metallic lines in the SMCstar spectra. This weakness is not the same for all thy metals and somecases may be attributable to physical phenomena which occur in theatmospheres of these luminous stars.
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IUE and ground-based observations of mass-loss in the Magellanic Clouds
Ground based and IUE observations of hot stars in the large and smallMagellanic Clouds were carried out to investigate the mass loss processin these objects and to search for differences with galactic hot stars.Preliminary results show that in a large proportion of the starsobserved the mass loss process is taking place. A mechanism foracceleration of the wind in OB stars is proposed.
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Coordinated ground-based and International Ultraviolet Explorer (IUE) observations of hot stars in the Magellanic Clouds
Ground based and International Ultraviolet Explorer (IUE) observationsof hot stars in the Large and Small Magellanic Clouds were carried outto investigate the mass loss process in these objects and to search fordifferences with galactic hot stars. Results show that in a largeproportion of the stars observed the mass loss process is taking place.A mechanism for acceleration of the wind in OB stars is proposed,involving multiple scattering of hard UB photons in the range 100A to500A.
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Structure and kinematics of the Small Magellanic Cloud as outlined by its brightest stars
Some basic properties of extreme Population I stars in the SmallMagellanic Cloud (SMC) are investigated on the basis of a systematicspectroscopic and photometric survey of the brightest supergiantsbelonging to the SMC. It is found that the main body and Wing of the SMCappear to have essentially the same mean radial velocity but that the K1region has a markedly different velocity. A differential distancemodulus of 0.50 + or - 0.07 is determined, along with an internal meanB-V color excess of 0.06 mag, a radial depth greater than that of theLarge Magellanic Cloud, and a disruption time of the order of 700million years.
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Additional radial velocities of supergiants in the Small Magellanic Cloud
Additional radial velocities of 28 SMC supergiants determined in theyears 1959-1969 at the Radcliffe Observatory are presented. These andother measures from ESO and elsewhere are intercompared. The meanRadcliffe velocities have an internal standard error of + or - 4.7 km/s,and a systematic error exceeding 4 km/s is regarded as unlikely. Eightstars in the SMC core have a corrected velocity dispersion of only 6.9km/s, similar to Feast's (1970) values for H II regions in the core. Butthe core H II regions have a velocity differential of -20 km/s relativeto these stars. The velocity dispersion for stars in other parts of theCloud is of the order of 15 km/s, as previously found. Two possiblyvariable-velocity stars are discussed without reaching a satisfactoryconclusion.
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Observations of supergiant stars in the Small Magellanic Cloud
Spectrographic and photometric data are presented for 91 supergiantstars belonging to the Small Magellanic Cloud and its Wing. The datainclude MK classes for 52 stars, radial-velocity data for 51 stars, andUBV photometry for 90 stars. In V the limiting magnitude for thespectrographic observations is 13.7 and for the photometricobservations, 13.9. Whenever possible, radial velocities forinterstellar Ca II and forbidden O II have been measured and listed.Notes are given for the individual stars concerning the data obtainedand comparisons with results of previous investigations.
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MK classification in the Small Magellanic cloud
This paper compares in detail the spectra of SMC supergiants with thoseof galactic supergiants. The helium and metallic lines are weaker in theformer, but not uniformly so for all metals. Also the Balmer jump issmall compared with standards, and some stars have quite large hydrogenprofiles. Other peculiar features are described.
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The brightest stars in the Small Magellanic Cloud.
Abstract image available at:http://adsabs.harvard.edu/abs/1973ApJ...181..327O
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BVRI-Photometry of the Brightest Stars in the Magellanic Clouds
We have made photometric observations in the BVRI system of 100 objectsthat belong to the Magellanic Clouds. The observational data indicate atleast two remarkable differences between some of the Magellanic Cloudobjects and the supergiant stars in the Galaxy, namely, the former aremore luminous than the most luminous galactic supergiants and they alsohave a color excess in V-R unexplained by interstellar extinction alone.Two possible explanations are likely for the additional color excess;either the presence of a circumstellar dust envelope or a differentchemical atmospheric composition from galactic supergiant stars, orperhaps both of them.
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Photometry of bright stars in the Small Magellanic Cloud.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970A&A.....9...95D&db_key=AST
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Polarization measurements of stars in the Magellanic Clouds.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970AJ.....75..778M&db_key=AST
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A finding list of proven or probable Small Magellanic Clouds members .
Abstract image available at:http://adsabs.harvard.edu/abs/1968AJ.....73..246S
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Equivalent widths of Hγ in stellar spectra of the Magellanic Clouds
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1966MNRAS.132..433H&db_key=AST
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