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Light variations of alpha Cygni variables in the Magellanic Clouds
We present time-series monitoring of 19 Magellanic Cloud super- andhypergiants, among which 13 alpha Cygni variables, viz.: S18 =AzV154, HDE268835 = R66, HD37974 = R126, HDE268757 = R59, HDE268822 =GV505, HDE269355 = GV258, HDE269612 = GV322, HDE270025 = GV439, AzV121,HD5277 = AzV136 = R10, AzV197, AzV310 = R26, and AzV369; the LMC starsHD32034 = GV80 = R62, HDE268819 = GV91, HDE269661 = GV346 = R111,HDE269697 = GV352, HDE269953 = GV423 = R150 and HDE270111 = GV460.
| A Spitzer Space Telescope Infrared Spectrograph Spectral Atlas of Luminous 8 μm Sources in the Large Magellanic Cloud
We present an atlas of Spitzer Space Telescope Infrared Spectrograph(IRS) spectra of highly luminous, compact, mid-IR sources in the LargeMagellanic Cloud. Sources were selected on the basis of IR colors and 8μm (Midcourse Space Experiment) fluxes indicative of highly evolved,intermediate-to-high-mass stars with current or recent mass loss atlarge rates. We determine the chemistry of the circumstellar envelopefrom the mid-IR continuum and spectral features and classify thespectral types of the stars. In the sample of 60 sources, we find 21 redsupergiants (RSGs), 16 C-rich asymptotic giant branch (AGB) stars, 11 HII regions, 4 likely O-rich AGB stars, 4 Galactic O-rich AGB stars, 2OH/IR stars, and 2 B[e] supergiants with peculiar IR spectra. We findthat the overwhelming majority of the sample AGB stars (with typical IRluminosities of ~104 Lsolar) have C-richenvelopes, while the O-rich objects are predominantly luminous RSGs withLIR~105 Lsolar. For both classes ofevolved star (C-rich AGB stars and RSGs), we use the near-to-mid-IRspectral energy distributions to determine mean bolometric correctionsto the stellar K-band flux densities. For carbon stars, the bolometriccorrections depend on the IR color, whereas for RSGs, the bolometriccorrection is independent of IR color. Our results reveal that objectspreviously classified as planetary nebulae on the basis of IR colorsare, in fact, compact H II regions with very red IRS spectra thatinclude strong atomic recombination lines and polycyclic aromatichydrocarbon emission features. We demonstrate that the IRS spectralclasses in our sample separate clearly in IR color-color diagrams thatuse combinations of Two Micron All Sky Survey data and synthetic SpitzerInfrared Array Camera and Multiband Imaging Photometer for Spitzerfluxes derived from the IRS spectra. On this basis we suggestdiagnostics to identify and classify, with high confidence levels,IR-luminous evolved stars and compact H II regions in nearby galaxiesusing Spitzer and near-IR photometry.
| Ionization structure in the winds of B[e] supergiants. II. Influence of rotation on the formation of equatorial hydrogen neutral zones
Context: .B[e] supergiants are known to have non-spherical winds, andthe existence of disks that are neutral in hydrogen close to theirstellar surface has been postulated. A suitable mechanism to producenon-spherical winds seems to be rapid rotation, and at least for threeB[e] supergiants in the Magellanic Clouds rotation velocities at asubstantial fraction of their critical velocity have been found.Aims: .We want to find suitable recombination distances in theequatorial plane of rapidly rotating stars that explain the observedhuge amounts of neutral material in the vicinity of B[e] supergiants. Methods: .We perform ionization structure calculations in theequatorial plane around rapidly rotating luminous supergiants. Therestriction to the equatorial plane allows us to treat the ionizationbalance equations 1-dimensionally, while the stellar radiation field iscalculated 2-dimensionally, taking into account the latitudinalvariation of the stellar surface parameters. The stellar parameters usedcorrespond to those known for B[e] supergiants. The assumptions made inthe computations all have in common that the total number of availableionizing photons at any location within the equatorial plane isoverestimated, resulting in upper limits for the recombinationdistances. Results: .We find that despite the drop in equatorialsurface density of rapidly rotating stars (neglecting effects likebi-stability and/or wind compression), hydrogen and helium recombine ator close to the stellar surface, for mass loss rates dot{M} ⪆5× 10-5 Mȯ yr-1 and rotationspeeds in excess of vrot, eq/v_crit ≃ 0.8.
| Spitzer Spectroscopy of Dusty Disks around B[e] Hypergiants in the Large Magellanic Cloud
We used the Spitzer Space Telescope Infrared Spectrograph (IRS) toobtain mid-infrared (5-35 μm) spectra of two highly luminous B[e]stars in the Large Magellanic Cloud (LMC), R126 (HD 37974) and R66 (HD268835). Both stars display flat spectra with silicate emissionfeatures; R66 displays, in addition, spectral evidence of crystallinegrains and PAHs. Given the similarity of the IRS spectra of R126 and R66to those of pre-main-sequence stars, we interpret these spectra as beingdue to thermal emission from circumstellar dust disks. Comparison with amodel of thermal emission from a passive, irradiated dust disk suggeststhat the disks around R126 and R66 are quite massive, with~3×10-3 Msolar of dust contained between 120and 2500 AU from the star in the case of R126. Episodic mass ejectionsand/or debris disks (perhaps surrounding as-yet undetected companionstars) represent potential sources for the thermal dust emission fromthese and other B[e] hypergiants in the LMC.
| Classification of Spectra from the Infrared Space Observatory PHT-S Database
We have classified over 1500 infrared spectra obtained with the PHT-Sspectrometer aboard the Infrared Space Observatory according to thesystem developed for the Short Wavelength Spectrometer (SWS) spectra byKraemer et al. The majority of these spectra contribute to subclassesthat are either underrepresented in the SWS spectral database or containsources that are too faint, such as M dwarfs, to have been observed byeither the SWS or the Infrared Astronomical Satellite Low ResolutionSpectrometer. There is strong overall agreement about the chemistry ofobjects observed with both instruments. Discrepancies can usually betraced to the different wavelength ranges and sensitivities of theinstruments. Finally, a large subset of the observations (~=250 spectra)exhibit a featureless, red continuum that is consistent with emissionfrom zodiacal dust and suggest directions for further analysis of thisserendipitous measurement of the zodiacal background.Based on observations with the Infrared Space Observatory (ISO), aEuropean Space Agency (ESA) project with instruments funded by ESAMember States (especially the Principle Investigator countries: France,Germany, Netherlands, and United Kingdom) and with the participation ofthe Institute of Space and Astronautical Science (ISAS) and the NationalAeronautics and Space Administration (NASA).
| Light variations of massive stars (alpha Cyg variables). XVIII. The B[e] supergiants S 18 in the SMC and R 66 = HDE 268835 and R 126 = HD 37974 in the LMC
We discuss photometric monitoring (VBLUW system) of three B[e]supergiants. All three objects appear to be variable. They are subjectto two (R 66 and R 126 in the LMC) and three (S 18 in the SMC) types oflight oscillations which range from a few days to years, and areprobably due to pulsations. We argue that a classification as alpha Cygvariables is justified. Their classification as mixed B[e]/S Dorvariables is less certain, though not impossible. Also based on othercases, a strong B[e]-S Dor variable connection seems to be present.Based on observations obtained at the European Southern Observatory atLa Silla, Chile.
| MSX, 2MASS, and the LARGE MAGELLANIC CLOUD: A Combined Near- and Mid-Infrared View
The Large Magellanic Cloud (LMC) has been observed by the MidcourseSpace Experiment (MSX) in the mid-infrared and the Two Micron All SkySurvey (2MASS) in the near-infrared. We have performed across-correlation of the 1806 MSX catalog sources and nearly 1.4 million2MASS cataloged point and extended sources and find 1664 matches. Usingthe available color information, we identify a number of stellarpopulations and nebulae, including main-sequence stars, giant stars, redsupergiants, carbon- and oxygen-rich asymptotic giant branch (AGB)stars, planetary nebulae, H II regions, and other dusty objects likelyassociated with early-type stars. A total of 731 of these sources haveno previous identification. We compile a listing of all objects, whichincludes photometry and astrometry. The 8.3 μm MSX sensitivity is thelimiting factor for object detection: only the brighter red objects,specifically the red supergiants, AGB stars, planetary nebulae, and H IIregions, are detected in the LMC. The remaining objects are likely inthe Galactic foreground. The spatial distribution of the infrared LMCsources may contribute to understanding stellar formation and evolutionand the overall galactic evolution. We demonstrate that a combined mid-and near-infrared photometric baseline provides a powerful means ofidentifying new objects in the LMC for future ground-based andspace-based follow-up observations.
| S 111 and the polarization of the B[e] supergiants in the Magellanic Clouds
We have obtained linear polarization measurements of the LargeMagellanic Cloud B[e] supergiant S 111 using optical imagingpolarimetry. The intrinsic polarization found is consistent with thepresence of an axisymmetric circumstellar envelope. We have additionallyestimated the electron density for S 111 using data from the literatureand revisited the correlation between polarization and envelopeparameters of the B[e] supergiant stars using more recent IR calibrationcolor data. The data suggest that the polarization can be indeedexplained by electron scattering. We have used Monte Carlo codes tomodel the continuum polarization of the Magellanic B[e] supergiants. Theresults indicate that the electron density distribution in theirenvelopes is closer to a homogeneous distribution rather than anr-2 dependence. At the same time, the data are best fitted bya spherical distribution with density contrast than a cylindricaldistribution. The data and the model results support the idea of thepresence of an equatorial disk and of the two-component wind model forthe envelopes of the B[e] supergiants. Spectropolarimetry would helpfurther our knowledge of these envelopes. Based on observations obtainedat the Cerro Tololo Inter-American Observatory.
| Observations and Modeling of B[e] Stars
We give a short definition of B[e] star and we show spectrocopicvariabilities obtained for the peculiar star HD 45677 especialy for thestrong He I line at 5876 Å. We present also some photometricobservations for this type of stars that show a important excess in thenear and mid infrared due to the presence of circumstellar dust. Themodeling of these stars shows that a simple model with a spherical dustshell fits well the observations. High spatial resolution gives anadditional constraint on the modeling.
| An improved classification of B[e]-type stars
We review the classification criteria for the B[e]-type stars (B typestars with forbidden emission lines in their optical spectrum) and weexpress these in terms of physical characteristics of the stars and thecircumstellar (CS) matter. We show on the basis of observations thatthese criteria can be met in different kinds of stars of different massand different evolutionary stages. We propose that the name "B[e]phen"is more appropriate than the name "B[e] stars". We propose thedefinition of five classes of stars which show the B[e]phen:B[e]gin{itemize} [(a)] B[e] supergiants or "sgB[e] stars" [(b)] pre-mainsequence B[e]-type stars or "HAeB[e] stars" [(c)] compact planetarynebulae B[e]-type stars or "B[e]ppn\ stars" [(d)] symbiotic B[e]-typestars or "SymB[e] stars" [(e)] unclassified B[e]-type stars or "unclB[e]stars" The primary and secondary classification criteria for each ofthese groups are defined. We also present lists of objects for eachgroup, except for the SymB[e] stars. It is possible that some starssatisfy the criteria for more than one of the classes sgB[e], HAeB[e],cPNB[e] and SymB[e]. In that case the evolutionary phase of the star isunclear and the star should be assigned to class unclB[e].
| Obscured AGB stars in the Magellanic Clouds. I. IRAS candidates
We have selected 198 IRAS sources in the Large Magellanic Cloud, and 11in the Small Magellanic Cloud, which are the best candidates to bemass--loosing AGB stars (or possibly post--AGB stars). We used thecatalogues of \cite[Schwering \& Israel (1990)]{ref42} and\cite[Reid et al. (1990)]{ref36}. They are based on the IRAS pointedobservations and have lower detection limits than the Point SourceCatalogue. We also made cross-identifications between IRAS sources andoptical catalogues. Our resulting catalogue is divided in 7 tables.Table \ref{tab1} lists optically known red supergiants and AGB stars forwhich we found an IRAS counterpart (7 and 52 stars in the SMC and LMC,respectively). Table \ref{tab2} lists ``obscured'' (or ``cocoon'') AGBstars or late-type supergiants which have been identified as such inprevious works through their IRAS counterpart and JHKLM photometry (2SMC and 34 LMC sources; no optical counterparts). Table \ref{tab3} listsknown planetary nebulae with an IRAS counterpart (4 SMC and 19 LMC PNe).Table \ref{tab4} lists unidentified IRAS sources that we believe to begood AGB or post--AGB or PNe candidates (11 SMC and 198 LMC sources).Table~\ref{tab5} lists unidentified IRAS sources which could be any typeof object (23 SMC and 121 LMC sources). Table \ref{tab6} lists IRASsources associated with foreground stars (29 SMC and 135 LMC stars).Table \ref{tab7} lists ruled out IRAS sources associated with HIIregions, hot stars, etc... We show that the sample of IRAS AGB stars inthe Magellanic Clouds is very incomplete. Only AGB stars more luminousthan typically 10^4 L_\odot and with a mass-loss rate larger thantypically 5 10^{-6} M_\odot/yr could be detected by the IRAS satellite.As a consequence, one expects to find very few carbon stars in the IRASsample. We also expect that most AGB stars with intermediate mass--lossrates have not been discovered yet, neither in optical surveys, nor inthe IRAS survey. Tables 1 to 8 are also available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| 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.
| B[e] phenomenon extending to lower luminosities in the Magellanic Clouds.
An analysis of the four recently discovered B[e] stars HenS35, S59, S93,and S137 in the Large Magellanic Cloud has been carried out usinglow-resolution IUE spectra, ESO 3.6-m CASPEC spectra, and ESO 0.5-m and1-m UBV and JHK photometry, respectively. LTE model atmospheres havebeen fitted to the observed continuum energy distributions in order toderive the stellar parameters. The results are T_eff_=22000K,R=28Rsun_, and logL/Lsun_=5.2 for HenS35,T_eff_=14000K, R=16Rsun_, and logL/Lsun_=4.0 forHenS59, and T_eff_=13000K, R=26Rsun_, andlogL/Lsun_=4.2 for HenS137. The presence of absorption linesin the optical spectrum of the B9[e]Ib star HenS93 allowed an additionalLTE line analysis for this star using Balmer, HeI, SIII, MgII, and FeIIlines to derive T_eff_=10000K, R=73Rsun_,logL/Lsun_=4.7, logg=1.75, ξ=10km/s, vsin i=65km/s, andM>14Msun_. Our investigation shows that the class of B[e]stars in the Magellanic Clouds extends to luminosities of aboutlogL/Lsun_=4, i.e. much lower than those of the previouslystudied B[e] supergiants. This result reinforces the importance of axialsymmetry in large regions of the Hertzsprung-Russell diagram.
| 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.
| Redshifts of high-luminosity stars - The K effect, the Trumpler effect and mass-loss corrections
The Trumpler effect is demonstrated in B and A supergiants in h + ChiPersei, as well as in other associations of young luminous stars. TheK-Trumpler effect is also shown in O, B, and A supergiants in theMagellanic Clouds, as well as in nearby galaxies such as NGC 1569 and2777 and in blue irregular variables in M31 and M33. Mass outflow inluminous stars is shown to require an average correction of about 20km/s and to increase the excess redshifts of the stars in the MagellanicClouds to a significance level of 6 sigma. Completely empirical andindependent measurements show that mass-loss corrections of this sizeare required on average for supergiants in both the SMC and LMC and alsoin the Milky Way.
| Polarization and the envelopes of B(e) supergiants in the Magellanic Clouds
We report optical linear polarization observations of nine B(e)supergiants in the Magellanic Clouds. Several of them have largeintrinsic polarizations. The data are consistent with nonsphericallysymmetric envelopes, around the B(e) stars, that possess a range ofintrinsic polarizations. Comparison of the polarimetric data with theviewing aspect, inferred from the spectroscopy of the individualobjects, agrees with this interpretation. The polarization correlatesbest with the infrared excess due to dust, suggesting the latter as thecause of most of the polarization. We cannot find, using the availabledata, a statistically significant difference between the polarizationdistributions of Galactic and Magellanic B(e) stars. Comparison of ourdata with previous polarimetric data, recovered from the literature forfour stars, seems to indicate that the envelopes are stable.
| OH/IR stars in the Magellanic Clouds
A group of IRAS sources in the LMC and SMC have been monitored in thenear infrared and pulsation period of over 1000 days have beendetermined for some of them. OH maser emission has been detected fromsome of the LMC objects. The OH line profiles indicate that stellar windvelocities in LMC stars are lower than in Galactic stars, a resultattributed to the lower metallicity in the LMC. Evidence is presentedthat reducing metallicity lowers mass loss rates from AGB stars providedthey do not turn into carbon stars. It is suggested that carbon starformation allows high mass loss rate to be maintained in AGB stars oflow metallicity. There is no convincing evidence that AGB stars evolvesignificantly beyond the classical AGB limit of M(bol) about -7.1.
| A search for T Tauri stars based on the IRAS point source catalog.
The results of the first part of a survey for new T Tauri stars, withspectroscopic and photometric observations of about 100 stars, arepresented. A list of candidates has been selected by means of the IRASPoint Source Catalog, based on appropriate far-infrared colors. Coudespectra of the selected objects in the 655-673 nm wavelength range,which includes H-alpha and the resonance Li I line, have been obtained.Thirty-three new T Tauri stars, and a number of other interestingobjects, like early type premain-sequence stars and Li-rich K giants,have been detected. Several new isolated T Tauri were found, includingHen 1, which may be the T Tauri star with the highest galactic latitudeknown, if its nature is confirmed.
| 1612 MHz OH survey of IRAS point sources. I - Observations made at Dwingeloo, Effelsberg and Parkes
The data from a large sky survey are presented including a northernpilot study and a detailed southern study in which detections are biasedtoward the most evolved sources and distant sources. Both areinvestigated at the 1612-MHz transition of OH to take advantage of thestrongest line for AGB stars with optically thick dust shells. The IRASsources are chosen by considering their IR colors related to fluxes at12, 25, and 60 microns. Observations are reported for 2703 IRAS pointsources at the 1612-MHz transition, and 738 OH/IR stars are detected.The survey identifies 597 of the sources as previously unidentified, and95 percent of the OH profiles observed have twin-peak masercharacteristics which are related to emission from expandingcircumstellar shells. The other 5 percent of the sources are concludedto be transition objects between OH/IR stars and planetary nebulae.
| Long-term photometry of variables at ESO. I - The first data catalogue (1982-1986)
This paper presents the catalog of photometric data in the Stromgrensystem obtained during the first four years (October 1982 - September1986) of the Long-Term Photometry of Variables (LTPV) program at ESO.The data are available in computer-readable form.
| S 18 - A new B(e) supergiant in the Small Magellanic Cloud with evidence for an excretion disk
High-SNR spectra of S 18 were obtained, and UBVRIJHK(L) magnitudes weremeasured. The line spectra display a forest of narrow emission lines ofsingly ionized (Si II, Ti II, VII, Cr II, Ni II, and Fe II) and neutral(Fe I and Ca I) metals, along with forbidden emission lines of Fe II, SII and O I. A broad emission feature at 6159 A has been identified as aTiO band. The present results can be explained using a Kurucz (1979)model with an effective temperature of 25,000 K, log g of about 3, andan IR excess due to ff-fb and dust radiation. It is concluded that S18is a B(e) supergiant with a high velocity wind in the polar region and aslow denser wind in the equatorial region which forms an excretion disk.
| A Provisory Catalogue of S-Doradus Candidate Stars in the Magellanic Clouds
Not Available
| IRAS Point Source Catalogue cross-identifications
Not Available
| CO overtone emission from Magellanic Cloud supergiants
A sample of 63 high-luminosity LMC supergiants has been searched forfirst-overtone CO emission at 2.3 microns. Six new CO emission starshave been found, showing that CO first-overtone emission is a commoncharacteristic of luminous stars with dense circumstellar envelopes andhaving a wide range of stellar temperatures. Of the non-CO emissionstars, eight have strong He I emission. Nine stars show CO absorption at2.3 microns from late-type companions. CO emission was not found in anyof the three LMC S Doradus variables, and the stars which do show COemission are not known to be photometrically variable.
| The galatic and LMC extreme line supergiants compared: IUE observations of the Henize-Carlson and Zoo star samples of massive supergiants
The Henize-Carlson sample of galactic massive supergiants, and acomparison between the Galactic and LMC samples are discussed. Severalof the stars, notably He3-395 and S 127/LMC, have very similar shellcharacteristics. There appears to be little difference, other thanluminosity, between the LMC and Galactic samples. One star, He3-1482,was detected with the Very Large Array at 6 cm. The UV data is combinedwith IRAS and optical information.
| Mass loss rates in the Hertzsprung-Russell diagram
Mass loss rates have been collected for 271 stars of spectral type Othrough M, primarily of population I. Good agreement is found forresults obtained according to six different methods, and it is shownthat the mass loss rate data can be well represented by one empiricalinterpolation formula as a function of the effective temperature andluminosity. The chemically evolved stars are shown to have mass lossrates which are larger than those of normal stars occupying the samepositions in the Hertzprung-Russell diagram by factors of 160 forWolf-Rayet stars and 11 for C-type stars.
| Singly ionized iron as a diagnostic of stellar envelopes. II - The structure of the envelopes of six luminous blue stars
The methods described in Friedjung and Muratorio (1987), involving theself-absorption curve for the Fe II optical emission lines and spectralsynthesis for the UV, are applied to study the surroundings of thegalactic P Cygni star AG Car and of five luminous Magellanic Cloudstars. Their Fe II emission and absorption spectra are interpreted byline formation in the same isotropic wind. In view of the difficultiesencountered using this approach for the Magellanic Cloud stars studied,simultaneous line formation in two different media, are considered andit is concluded that, in those stars, emission lines are most easilyunderstood as formed in a region not in front of the photosphere(probably a dense disk). It does appear that for two of the sample stars(R50 and R82), layers of the disk which are optically thin in thecontinuum produce the observed Fe II absorption lines, while for twoother stars (R66 and S22) the absorption spectrum is due to a wind. Inthe case of the galactic star AG Car the wind is responsible for the FeII emission spectrum as well as for the observed Fe II absorptionspectrum.
| P Cygni type stars.
Not Available
| Circumstellar Dust in the Vicinity of Luminous Blue Variables
Not Available
| B(e)-supergiants of the Magellanic Clouds
Spectroscopic and photometric observations at the satellite UV, visual,and infrared wavelengths of eight Magellanic Cloud dustyB(e)-supergiants (R 4, R 50, R 66, R 82, R 126, Hen S 12, Hen S 22, andHen S 134) are discussed. In spite of their high luminosity, these starsshow little or no photometric or spectroscopic variations. Apart from R66 (B8Ia) all stars are early B supergiants (B0-B3). The peculiaremission line spectra appear to be a consequence of unique windcharacteristics. A two component stellar wind and a normal radiationdriven wind in the polar region, can account for the observations. It isconcluded that the known B(e)-stars of the Magellanic Clouds are massivepost-main-sequence objects where stellar rotation plays an importantrole for the mass loss.
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Osservazione e dati astrometrici
| Costellazione: | Mensa |
| Ascensione retta: | 04h56m47.08s |
| Declinazione: | -69°50'24.7" |
| Magnitudine apparente: | 10.853 |
| Moto proprio RA: | -0.9 |
| Moto proprio Dec: | -0.7 |
| B-T magnitude: | 10.892 |
| V-T magnitude: | 10.857 |
Cataloghi e designazioni:
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