Red supergiants in the LMC - IV: Calibration of intrinsic colours and the HRD
A new calibration of the (B-V)0, (V-R)0 and(V-I)0 colours in the Kron-Cousins system for F to Msupergiants and of the (V-K)0 colours in the SAAO system of Kto M supergiants in the LMC as measures of effective temperature andbolometric correction is given. For F to G supergiants the theoreticalTeff-intrinsic colour- relations given by Lejeune et al.(1997) on the basis of their own model atmospheres agree mostly wellwith our observations. For K to M supergiants, however, their intrinsiccolours are too red in most cases. The relations given by Bessell et al.(1998) based on the model atmospheres of Plez (1997) fit theobservations better, but their synthetic colours are often also too red.The calibration of the bolometric correction is not reproduced well byany of the models. The HRD of the stars shows two distinct groups, onewith log Teff above 3.80 and one with log Teffbetween 3.53 and 3.62. The upper luminosity and therefore the mass limitdepends significantly on effective temperature. The F to G stars haveMbol up to -9.8 mag (corresponding to 45 Msun),while the K to M stars do not exceed - -9.0 mag (corresponding to 31Msun). Neither the Geneva nor the Padova models can fit thepositions of the most luminous and the coolest supergiants. Thediscrepancy between theory and observation increases both withincreasing mass loss rate and overshooting. Best agreement with theobservations is reached by assuming mass loss rates of 2/3 of the deJager et al. (1988) mass loss rates. As shown both by the luminosity andinitial mass function, very luminous (i.e. massive) stars areoverproportionally rare. With -3.73 +/- 0.20 the slope of the initialmass function is very steep in the considered range of 16-35Msun, but confirms the results obtained by Massey et al.(1995) from an extensive study of the field OB stars both in theMagellanic Clouds and the Galaxy.
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Red supergiants in the LMC - III: luminous F and G stars
New BVRI observations for 40 and spectrophotometric measurements for 23F to G LMC supergiant candidates (and 3 galactic F to G supergiants) arepresented. The errors of the BVRI data are 0.01 to 0.03 mag in mostcases. The wavelength range of the spectra is 3400 to 6400 Angstroms,their resolution 10 Angstroms. The mean error of the fluxes is 0.03 mag.Spectral indices measuring the strengths of the Hβ , Hγ ,Hdelta , NaD and CaII H+K lines, the CHα_ {0} and CNbeta_ {0}bands, of the Balmer jump and the slope of the continuum redwards arediscussed as measures of effective temperature and luminosity on thebasis of galactic stars with accurate MK types and parallaxes. TheHγ line and the continuum gradient are very good temperaturecriteria, the CHα_ {0} band and especially the Balmer jump forluminosity. The luminosity classification given for F to G supergiantcandidates in the LMC in the literature is often doubtful. 5 of the 23stars observed spectrophotometrically turn out to be probably galacticforeground dwarfs on the basis both of the Balmer jump and thecomparison of their flux distributions with synthetic ones based on theKurucz model atmospheres. Surface gravities derived purely on the basisof flux distributions and such ones given by models of stellar evolutionagree with each other for dwarfs and giants only. For supergiants theformer are about 1.0 dex higher than the latter. As a consequenceeffective temperatures and metallicities given by these two methodsdeviate from each other for such stars, too. The intrinsic colours andtemperatures of galactic and LMC supergiants do not differ. Withabsolute magnitudes up to -9.6 mag the upper luminosity limit in the LMCdoes not exceed that in the Galaxy, where Ia-0 supergiants haveMV of up to -9.5 mag. The metallicities of the supergiantsshow a rather large scatter. Nevertheless the mean metallicities of 0.02+/- 0.09 dex for the Galaxy and -0.26 +/- 0.10 dex for the LMC agreewell with other observations.
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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.
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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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Luminosities of yellow supergiants from near-infrared spectra - Calibration through Magellanic Cloud stars
The possibility of using medium resolution spectrograms in the nearinfrared region to determine luminosities of A-G supergiants has beenexplored. A sample of 49 of these stars has been observed in the twoMagellanic Clouds, and using the intensities of the O I 7774 triplet andan index (CP), which is a combination of the Ca II triplet and Paschenlines intensities, a preliminary luminosity calibration, based on LMCstars, has been obtained. Such a calibration predicts reliableluminosities for Galactic supergiants, and offers the advantage of beingcompletely reddening independent. The reddening free CP index combinedwith BVRI color indices has also been used to estimate the interstellarreddenings of Magellanic Cloud stars.
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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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The distance to the Magellanic Clouds from luminous F supergiants
A recent M(v)-uvby beta calibration for Galactic luminous F-Gsupergiants was used to estimate the distance to the Magellanic Cloudsfrom F supergiants. The distance moduli 19.33 + or - 0.31 for the SMCand 18.19 + or - 0.22 for the LMC are found. The present limitations ofusing F-G supergiants as distance indicators are discussed.
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The calibration of the Stromgren photometric system for A, F and early G supergiants. I - The observational data
An empirical calibration of the Stromgren uvby-beta photometric systemfor the A, F, and early G supergiants is being derived. This paperexplains the observational program and the photometric reductiontechniques used and presents a catalog of new Stromgren photometry forover 600 A, F, and G supergiants.
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Photometric Studies of Magellanic Cloud Supergiants. II. Variability
Abstract image available at:http://adsabs.harvard.edu/abs/1986ApJS...62..451G
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Photometric studies of Magellanic Cloud supergiants. I - Mean magnitudes and reddenings. II - Variability
In the first part of this paper, a combination of spectral types for 81LMC and 46 SMC supergiants from the literature with new BVRI photometryyields reddenings and intrinsic colors for these stars. While reddeningsup to E(B-V) of 0.3 are found for the LMC sample, the figure for the SMCappears to be no more than 0.2. The dust/gas ratio in both galaxies isfound to be lower than in the Milky Way. In the second part, individualBVRI photoelectric observations for 88 LMC and 46 SMC intermediatespectral type supergiants are analyzed for variability. It is noted that45 percent of the stars exhibit significant variations, with theincidence of variability decreasing with decreasing luminosity.
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Radial velocities of southern stars obtained with the photoelectric scanner CORAVEL. V - 404 F to M supergiant stars in the Large Magellanic Cloud
High accuracy radial velocities have been obtained for 404 F and Msupergiant stars belonging to the LMC using the photoelectric scannerCORAVEL. The observations are presented and the determination of theaccuracy is described. The results are compared to the previous work ofFeast et al. (1960), Ardeberg et al. (1972), and Brunet et al. (1973),and a new determination of the average velocity dispersion in the LMC isgiven. The general trend of the stellar velocities, as compared to theradial velocities of gaseous components, is examined. A systematic shiftof about 6 km/s between velocities of KM and OBA stars is observed,while agreement is excellent with H I velocities. The surfacedistribution of radial velocities shows a tendency of stars to clusterin groups with low intrinsic velocity dispersions. A preliminary meanvelocity dispersion of 5.3 km/s is determined for KM stars.
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Leavitt variables - Bright variable supergiants and their implications for the distance scale
BVRI photometric observations of the LMC supergiants S65 - 08 and S65 -48, obtained using the 61-cm reflector at the University of Toronto aspart of an intermediate-supergiant monitoring program (Grieve, 1983),are reported and analyzed along with published data. The data arepresented in tables and graphs, and both stars are found to have lightvariations (about 0.2 mag in V) with periods of about 250 d and H-bandmagnitudes consistent with positions on a linear extrapolation of theLMC Cepheid period/luminosity relation toward higher luminosity. It issuggested that detection of similar long-period low-amplitude variablesin other galaxies would permit determination of accurate distances up tom-M = about 30 mag.
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The reddening, metal abundance, and luminosity of high-luminosity G-type stars
The abundance parameters of the sample of 100 G-type bright giants andsupergiants whose photometry is presently discussed indicate Fe/H valuesof between about + 0.6 dex and the solar value, using a preliminarycalibration of the photometric indices. The few long period Cepheidsthat are not heavily blanketed F-type stars give reddening values thatare in agreement with current results from other methods of analysis.Supergiants show no clear gradients in the galactic distribution ofabundances, and those nearest the sun range from an Fe/H of about + 0.3dex, for members of the Pleiades Group, to near solar abundance. A smallsample of Large Magellanic Cloud supergiants shows nearly the same rangein metal abundance as the galactic stars, and gives a modulus for thisCloud of 18.3 + or - 0.20 mag.
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DDO Observations of Southern Stars
Not Available
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Finding list and spectral classifications for southern luminous stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1976AJ.....81..225M&db_key=AST
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BVI Photometry of LMC Supergiants
Not Available
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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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Additional observations of supergiants and foreground stars in the direction of the Large Magellanic Cloud
Abstract image available at:http://adsabs.harvard.edu/abs/1973A&AS....9..447B
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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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The Strength of the O i ?7774 Line in the Brightest Stars in the Megellanic Clouds
Abstract image available at:http://adsabs.harvard.edu/abs/1972ApJ...171..393O
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A deep objective-prism survey for Large Magellanic Cloud members
Not Available
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Studies in the Magellanic Clouds VI,
Not Available
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INHABITED SKY
