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Публикации по объекту
Models for Massive Stellar Populations with Rotation
We present and discuss evolutionary synthesis models for massive stellarpopulations generated with the Starburst99 code in combination with anew set of stellar evolution models accounting for rotation. The newstellar evolution models were compiled from several data releases of theGeneva group and cover heavy-element abundances ranging from twice solarto one-fifth solar. The evolution models were computed for rotationvelocities on the zero-age main sequence of 0 and 300 km s-1and with the latest revision of stellar mass-loss rates. Since the masscoverage is incomplete, in particular at nonsolar chemical composition,our parameter study is still preliminary and must be viewed asexploratory. Stellar population properties computed with Starburst99 andthe new evolution models show some marked differences in comparison withmodels obtained using earlier tracks. Since individual stars now tend tobe more luminous and bluer when on the blue side of theHertzsprung-Russell diagram, the populations mirror this trend. Forinstance, increases by factors of 2 or more are found for thelight-to-mass ratios at ultraviolet to near-infrared wavelengths, aswell as for the output of hydrogen-ionizing photons. If these resultsare confirmed once the evolution models have matured, recalibrations ofcertain star formation and initial mass function indicators will berequired.
| Understanding B-type supergiants in the low metallicity environment of the SMC II
Despite a resurgence of effort over the last decade in the area ofmassive stars there is still ambiguity over their evolutionary path,contamination of their surface abundances and the behaviour of theirstellar winds. Here 10 SMC B-type supergiants are analysed applying aunified model atmosphere code fastwind to intermediate resolutionspectra from the ESO Multi Mode Instrument (emmi) on the NTT telescope.Combined with the 8 targets analysed in Paper I (Trundle et al. 2004),this work provides observational results on the properties of the windsand chemical compositions of B-type supergiants in the SMC. This paperemphasizes and substantiates the implications for stellar evolution fromPaper I; that current theoretical models need to produce larger degreesof surface nitrogen enhancements at lower rotational velocities. Inaddition a significant discrepancy between theoretical and observedmass-loss rates is discussed which will have important implications forthe rotational velocities obtained from stellar evolution calculations.Furthermore, an initial calibration of the wind-momentum luminosityrelationship for B-type supergiants in a low metallicity environment (Z= 0.004) is presented.
| 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.
| VBLUW photometry of fifteen alpha CYG variables (including LBVs) in the Galaxy, the LMC and the SMC
VBLUW photometry (Walraven system) of 15 alpha Cyg-type variables,(luminous massive stars), including 10 LBVs and one suspected LBV arepresented. Formulae are given to transform the V and V-B of the Walravensystem to V and B-V of the Johnson UBV system.
| Light variations of massive stars (alpha Cyg variables). XVI. The LMC supergiants R 85 (LBV) and R 110 (LBV) and the SMC supergiants R 42 and R 45
Multi-colour photometry of four variable supergiants in the LMC and SMC,viz. R 85, R 110, R 42 and R 45, is searched for periods, studied anddiscussed. The suspected LBV R 85 is undoubtedly an active LBV, thoughnot as spectacular as R 110. Their microvariations superimposed on the SDor-activity are analyzed as well as those exhibited by R 42 and R 45.Often, a period search is difficult because of the very complicatedmicro-variability. We suggest that this is caused by an intricatemulti-cyclic behaviour combined with stochastic processes. The length ofthe strongest cyclicity in the power spectrum of R 42 (128 d) is of theorder of the rotation periods of BA-type supergiants. In connection withour findings described in the present paper and the previous ones, wediscuss various competing theoretical models on the instability of alphaCyg variables, including the LBVs. Based on observations obtained at theEuropean Southern Observatory at La Silla, Chile (observing proposals55D-0317, 56D-0249, 57D-0133 and 58D-0118)
| HIPPARCOS photometry of 24 variable massive stars (alpha Cygni variables)
The photometric variability of 24 alpha Cyg variables, i.e. variablesuper-and hypergiants, observed by the Hipparcos satellite is described.Three of the selected stars are situated in the SMC, 12 in the LMC andthe remaining 9 in the Galactic plane. Four of them are hot S Dor-typevariables, or LBVs (luminous blue variables) and two are possiblemembers of this class. Light curves are presented for all stars. Forfive stars, among which one LBV, the variability was discovered from theHipparcos photometric data. Results of period searches are presentedand, when relevant, folded light curves are shown. The linear ephemerisof two variables was revised. For most of the program stars theHipparcos magnitude scale (Hp) differs from the V of the UBV system byla 0fm1 . For all variables temperatures and M_bol are given. Galacticforeground reddening for the objects in the Magellanic Clouds are givenbased on IRAS maps.
| UV Spectral Classification of O and B Stars in the Small Magellanic =
We present an ultraviolet classification system for 0 and B stars of theSmall Magellanic Cloud (SMC). This system is defined by a set ofstandard, low resolution, International Ultraviolet Explorer (JUE)spectra. This UV classification system results from the development ofspectral sequences demonstrating systematic patterus of UV spectralfeatures. These spectral sequences yield Uv classifications for 133 0and B stars of the SMC, which we also present here. Although independentof the MK System, our UV classifications show general agreement withthose deduced from visual data. This UV classification system isdesigned to be applicable to 0 and B stars in other nearby galaxies ofmetallicity comparable to the SMC. The classification technique itselfis applicable to any UV dataset of sufficient size and quality, and canbe used to extend our UV classification system to other galactic metalabundances. These UV classification systems will be essential foranalysis of datasets from new spaceborne instrumentation such as theSpace Telescope Imaging Spectrograph (STIS), which will be capable ofobserving stars in external galaxies for which no opticalclassifications exist. 0 1997 American Astronomical Society.[S0004-6256(97)0231 1-X]
| 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.
| 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.
| 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.
| 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.
| 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.
| 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).
| 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.
| Small Magellanic Cloud: H-gamma-line equivalent widths and luminosity classes of the brightest blue star members
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1987A&AS...69..421A&db_key=AST
| 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
| 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
| 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.
| Ultraviolet interstellar absorption toward stars in the Small Magellanic Cloud. III - The structure and kinematics of the Small Magellanic Cloud
The structural and kinematic properties of the Small Magellanic Cloud(SMC) were studied by combining IUE satellite observations of individualbright stars (Sk 159 and HD 5980) with existing optical and radio data.It is shown that the SMC has a complex structure due to gravitationalinteraction with the Milky Way and the Large Magellanic Cloud (LMC).Stars observed in the southwest regions of the SMC were associated withthe 134 km/s H I complex. H II regions in the SMC were distributedaccording to a rotational velocity of 167 km/s. All IUE high-dispersiontargets exhibit ultraviolet absorption near 100 km/s and 200 km/s. It isshown that the absorption arises in the widespread H I complexes atvelocities similar to the H II regions. Some possible explanations forthe origin of H II and H I regions in the SMC are discussed. Thelocations of the nine high-dispersion IUE targets in the SMC are given.
| Interstellar CA II lines in SMC stars
Interstellar Ca II lines of reddened early-type stars in the SMC wereobserved. In addition to the component from the Milky Way, strong lineswere detected at radial velocities corresponding to gas in the SMC. Theinterstellar Ca II lines are abnormally strong, given the small colorexcesses of the stars and the low metallicity of the SMC gas, whichsuggests that the grains contain a much smaller fraction of theinterstellar calcium than they do in the galaxy. The radial velocitiesdo not conflict with the two-galaxy model for the SMC of Matthewson andFord (1983) if the higher-velocity system is behind the lower-velocitysystem.
| A comparison between various UV photometric systems for late-type stars
Ultraviolet absolute photometry and spectrophotometry obtained forlate-type stars with the TD1, OAO-2, ANS, and IUE satellites arecompared. Strong colour effects are found in the TD1 2740 Å band,and, to a lesser extend, in the OAO-2 2980 Å band. The reason forthese effects is believed to be due to red leaks in the sensitivityfunctions. For the TD1 band at 2365 Å a strong non-linearity atlow flux levels is found. The OAO-2 spectrophotometry is found to besignificantly influenced by scattered light for late-type stars. The ANSphotometry and the IUE LWR spectrophotometry are found to be withoutlarge systematic errors. As a corollary the authors give intrinsic UVcolours for late-type stars.
| 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.
| Catalogue of the Small Magellanic Cloud star members
This catalogue contains 524 Small Magellanic Cloud members locatedbetween 0.51 h and 1.22 h in right ascension for the epoch 1975.0.Equatorial coordinates, localization of stars with respect to thecomplexes of ionized hydrogen and information about possible closeoptical companions are given. Photoelectric photometric UBV data,spectral classifications and radial velocities published by variousauthors are listed as well in this catalogue. A master set and 17identification astrographic charts including one panelled chart forisolated members are provided.
| 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.
| International ultraviolet explorer spectroscopy of hot stars in the LMC and SMC - The SMC extinction law, stellar flux distributions, and details of the stellar winds
IUE high- and low-dispersion spectral observations of hot stars in theSmall Magellanic Cloud and Large Magellanic Cloud are presented. Theextinction curve for the SMC derived from the data is much steeper inthe UV than those of the LMC or the Galaxy. Based on stellar continuumdata, stellar temperatures in the Magellanic Clouds are found to benormal and consistent with their spectral types, and the H-R diagramshows most stars to be evolved. Strong, sharp-sided absorption linesfound in the UV spectra are found to vary with stellar spectral type,and are identified with stellar winds, which are much weaker in theMagellanic Clouds than in the Galaxy. These wind data may haveimplications for stellar mass loss rates and resultant stellar masses inthe SMC and LMC.
| The Galactic Foreground Reddening in the Direction of the Magellanic Couds
Abstract image available at:http://adsabs.harvard.edu/abs/1980PASP...92..587M
| Calcium abundances of F supergiants in the Magellanic Clouds
Abstract image available at:http://adsabs.harvard.edu/abs/1980AJ.....85..848S
| Stellar winds from hot stars in the Magellanic Clouds
Spectrographic data have been obtained of O and B supergiants in theMagellanic Clouds at dispersions 12 and 25 A/mm in the blue and 25 and50 A/mm in the red. Mass loss phenomena, line radial velocities, andline intensities have been measured on them and are compared withsimilar data on galactic stars. There appear to be some differencesbetween the SMC, LMC, and the Galaxy in all these respects. Mass loss isclearly occurring in the Magellanic Cloud stars, and the SMC stars haveparticularly discrepant line intensities.
| 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.
| On the spectrographic and photometric data for the brightest stars in the Small Magellanic Cloud
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1979A&A....77..269A&db_key=AST
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Группы:
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Наблюдательные данные и астрометрия
| Созвездие: | Тукан |
| Прямое восхождение: | 01h09m03.96s |
| Склонение: | -72°32'17.7" |
| Видимая звёздная величина: | 11.05 |
| Собственное движение RA: | 2 |
| Собственное движение Dec: | -5.2 |
| B-T magnitude: | 10.868 |
| V-T magnitude: | 11.035 |
Каталоги и обозначения:
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