Садржај
Слике
Уплоадјуј своје слике
DSS Images Other Images
Везани чланци
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.
| Light variations of massive stars (α Cyg variables). XIX. The late-type supergiants R 59, HDE 268822, HDE 269355, HDE 269612 and HDE 270025 in the LMC
We present and discuss VBLUW photometry (Walraven system) of fivesupergiants in the LMC. For one well-known variable, the hypergiant R 59= HDE 268757 (G7 Ia+) also Hipparcos photometry and numerousvisual observations are available. The second variable is HDE 269612 (F0Ia), and a third one is HDE 268822 (F6 Ia). Two F6 Ia supergiants turnedout to be constant: HDE 269355 and HDE 270025.Partly based on observations obtained at the European SouthernObservatory at La Silla, Chile.
| New periodic variables from the Hipparcos epoch photometry
Two selection statistics are used to extract new candidate periodicvariables from the epoch photometry of the Hipparcos catalogue. Theprimary selection criterion is a signal-to-noise ratio. The dependenceof this statistic on the number of observations is calibrated usingabout 30000 randomly permuted Hipparcos data sets. A significance levelof 0.1 per cent is used to extract a first batch of candidate variables.The second criterion requires that the optimal frequency be unaffectedif the data are de-trended by low-order polynomials. We find 2675 newcandidate periodic variables, of which the majority (2082) are from theHipparcos`unsolved' variables. Potential problems with theinterpretation of the data (e.g. aliasing) are discussed.
| HST study of the LMC compact star-forming region N83B
High resolution imaging with the Hubble Space Telescope has uncoveredthe thus far hidden stellar content and the nebular features of the highexcitation compact H ii region N83B in the Large Magellanic Cloud (LMC).We discover that the H ii region is powered by the most recent massivestarburst in the OB association LH 5 and the burst has created about 20blue stars spread over ~ 30'' on the sky (7.5 pc). Globally N83Bdisplays a turbulent environment typical of newborn massive starformation sites. It contains an impressive ridge, likely created by ashock and a cavity with an estimated age of only ~ 30 000 yr, sculptedin the ionized gas by the powerful winds of massive stars. Theobservations bring to light two compact H ii blobs, N83B-1 and N83B-2,and a small arc-nebula, N83B-3, lying inside the larger H ii region.N83B-1, only ~ 2''.8 (0.7 pc) across, is the brightest and most excitedpart of N83B. It harbors the presumably hottest star of the burst and isalso strongly affected by dust with an extinction of AV=2.5mag. The second blob, N83B-2, is even more compact, with a size of only~ 1'' (0.3 pc). All three features are formed in the border zone betweenthe molecular cloud and the ionized gas possibly in a sequential processtriggered by the ionization front of an older H ii region. Our HSTimaging presents an interesting and rare opportunity to observe detailsin the morphology of star formation on very small spatial scales in theLMC which are in agreement with the concept of the fractal structure ofmolecular star-forming clouds. A scenario which supports hierarchicalmassive star formation in the LMC OB association LH 5 is presented.Based on observations with the NASA/ESA Hubble Space Telescope obtainedat the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS 5-26555.
| The Progenitor Masses of Wolf-Rayet Stars and Luminous Blue Variables Determined from Cluster Turnoffs. I. Results from 19 OB Associations in the Magellanic Clouds
We combine new CCD UBV photometry and spectroscopy with those from theliterature to investigate 19 Magellanic Cloud OB associations thatcontain Wolf-Rayet (W-R) and other types of evolved, massive stars. Ourspectroscopy reveals a wealth of newly identified interesting objects,including early O-type supergiants, a high-mass, double-lined binary inthe SMC, and, in the LMC, a newly confirmed luminous blue variable (LBV;R85), a newly discovered W-R star (Sk -69°194), and a newly foundluminous B[e] star (LH 85-10). We use these data to provide precisereddening determinations and construct physical H-R diagrams for theassociations. We find that about half of the associations may be highlycoeval, with the massive stars having formed over a short period(Δτ<1 Myr). The (initial) masses of the highest massunevolved stars in the coeval clusters may be used to estimate themasses of the progenitors of W-R and other evolved stars found in theseclusters. Similarly, the bolometric luminosities of the highest massunevolved stars can be used to determine the bolometric corrections(BCs) for the evolved stars, providing a valuable observational basisfor evaluating recent models of these complicated atmospheres. What wefind is the following: (1) Although their numbers is small, it appearsthat the W-R stars in the SMC come from only the highest mass (greaterthan 70 Msolar) stars. This is in accord with ourexpectations that at low metallicities only the most massive andluminous stars will have sufficient mass loss to become W-R stars. (2)In the LMC, the early-type WN (WNE) stars occur in clusters whoseturnoff masses range from 30 to 100 Msolar or more. Thissuggests that possibly all stars with mass greater than 30Msolar pass through a WNE stage at LMC metallicities. (3) Theone WC star in the SMC is found in a cluster with a turnoff mass of 70Msolar, the same as that for the SMC WN stars. In the LMC,the WC stars are found in clusters with turnoff masses of 45Msolar or higher, similar to what is found for the LMC WNstars. Thus we conclude that WC stars come from essentially the samemass range as do WN stars and indeed are often found in the sameclusters. This has important implications for interpreting therelationship between metallicity and the WC/WN ratio found in LocalGroup galaxies, which we discuss. (4) The LBVs in our sample come fromvery high mass stars (greater than 85 Msolar), similar towhat is known for the Galactic LBV η Car, suggesting that only themost massive stars go through an LBV phase. Recently, Ofpe/WN9 starshave been implicated as LBVs after one such star underwent an LBV-likeoutburst. However, our study includes two Ofpe/WN9 stars, BE 381 and Br18, which we find in clusters with much lower turnoff masses (25-35Msolar). We suggest that Ofpe/WN9 stars are unrelated to``true'' LBVs: not all ``LBV-like outbursts'' may have the same cause.Similarly, the B[e] stars have sometimes been described as LBV-like.Yet, the two stars in our sample appear to come from a large mass range(30-60 Msolar). This is consistent with other studies,suggesting that B[e] stars cover a large range in bolometricluminosities. (5) The bolometric corrections of early WN and WC starsare found to be extreme, with an average BC(WNE) of -6.0 mag and anaverage BC(WC4) of -5.5 mag. These values are considerably more negativethan those of even the hottest O-type stars. However, similar valueshave been found for WNE stars by applying Hillier's ``standard model''for W-R atmospheres. We find more modest BCs for the Ofpe/WN9 stars(BC=-2 to -4 mag), also consistent with recent analysis done with thestandard model. Extension of these studies to the Galactic clusters willprovide insight into how massive stars evolve at differentmetallicities.
| UBV photometry of Galactic foreground and LMC member stars - III. LMC member stars - a new data base
New UBV photometry for 878 luminous member stars of the Large MagellanicCloud (LMC) and 13 stars of uncertain membership is presented. The datawill be available at Centre de Données astronomiques deStrasbourg. Including former observations now UBV data are available foraltogether 2470 luminous LMC stars and 2106 foreground stars plus 65stars of uncertain membership. The observations have been used alreadyfor several investigations dealing e.g. with interstellar reddeninglines and intrinsic colours, the dust distribution and the calibrationof charge-coupled device exposures.
| 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.
| 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.
| The yellow hypergiants
We list the main stellar data of known hypergiants and similarlyluminous stars, and then concentrate on a review of the yellowhypergiants. These stars are post-red supergiants evolving alongblueward loops in the Hertzsprung-Russell diagram. Their properties,their location in the Hertzsprung-Russell diagram and their occasionalmass ejections are related to a region of atmospheric instability in theH-R diagram, the Yellow Void. The `bouncing against the border of theVoid' of three objects: ρ Cas, HR8752 and IRC+10420, is described.The apparent atmospheric instability of yellow hypergiants is related tothe atmospheric pulsations. There are indications that the approach tothe Void is associated with an increased amplitude of the pulsation andwith enhanced mass loss. The observed small-scale motion field is onlyapparently strongly supersonic; the observed large stochastic velocitiesare the quasi-stochastically varying thermal motions in the many hotsheets that occur in the wakes of many small shocks, while the realhydrodynamic velocity component is small and subsonic. This shock-wavefield is also responsible for the observed rate of mass loss and foremission in the wings of Hα . Most yellow hypergiants haveenvelopes containing gas and dust, but a thick extended envelope,presumably dissipating and showing bipolar outflow, is only known aroundIRC+10420. At the interface of the bipolar wind and the interstellarmedium one or more stationary shocks may develop as is observed in thecase of IRC+10420 and suspected with ρ Cas.
| A catalogue of [Fe/H] determinations: 1996 edition
A fifth Edition of the Catalogue of [Fe/H] determinations is presentedherewith. It contains 5946 determinations for 3247 stars, including 751stars in 84 associations, clusters or galaxies. The literature iscomplete up to December 1995. The 700 bibliographical referencescorrespond to [Fe/H] determinations obtained from high resolutionspectroscopic observations and detailed analyses, most of them carriedout with the help of model-atmospheres. The Catalogue is made up ofthree formatted files: File 1: field stars, File 2: stars in galacticassociations and clusters, and stars in SMC, LMC, M33, File 3: numberedlist of bibliographical references The three files are only available inelectronic form at the Centre de Donnees Stellaires in Strasbourg, viaanonymous 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.
| 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.
| A catalogue of Fe/H determinations - 1991 edition
A revised version of the catalog of Fe/H determinations published by G.Cayrel et al. (1985) is presented. The catalog contains 3252 Fe/Hdeterminations for 1676 stars. The literature is complete up to December1990. The catalog includes only Fe/H determinations obtained from highresolution spectroscopic observations based on detailed spectroscopicanalyses, most of them carried out with model atmospheres. The catalogcontains a good number of Fe/H determinations for stars from open andglobular clusters and for some supergiants in the Magellanic Clouds.
| The Perkins catalog of revised MK types for the cooler stars
A catalog is presented listing the spectral types of the G, K, M, and Sstars that have been classified at the Perkins Observatory in therevised MK system. Extensive comparisons have been made to ensureconsistency between the MK spectral types of stars in the Northern andSouthern Hemispheres. Different classification spectrograms have beengradually improved in spite of some inherent limitations. In thecatalog, the full subclasses used are the following: G0, G5, G8, K0, K1,K2, K3, K4, K5, M0, M1, M2, M3, M4, M5, M6, M7, and M8. Theirregularities are the price paid for keeping the general scheme of theoriginal Henry Draper classification.
| A list of MK standard stars
Not Available
| 1988 Revised MK Spectral Standards for Stars GO and Later
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.
| UBV photoelectric catalogue (1986). II - Analysis
The UBV photoelectric data of the stars presenting several entries inthe 1986 edition of the UBV catalog have been systematicallyintercompared, and this paper presents a discussion of the stars forwhich discrepancies larger than 0.2 mag were found. Thirty-six probablyvariable stars have been detected, among which 18 are Be stars. Sixtyfurther stars present differences in the V magnitude larger than 0.2mag. Sixteen stars already appear in the NSV catalog. Although manyproblems are probably due to poor observations, new (eclipsing) variablestars may be found in this sample. Complete disagreement is foundbetween the values published from two independent sources in 34 cases. Afirst analysis of the quality of the UBV data shows that 65 percent ofthe differences in the V magnitude and in U-B color, for respectively11,500 and 7200 stars with two sources of data, are smaller than 0.04.The scatter on the B-V index appears to be smaller, since the samepercentage reaches 79 percent.
| UBV Photoelectric Photometry Catalogue (1986). III Errors and Problems on DM and HD Stars
Not Available
| Photometric Studies of Magellanic Cloud Supergiants. II. Variability
Abstract image available at:http://adsabs.harvard.edu/abs/1986ApJS...62..451G
| 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.
| 1985 revised MK spectral standards : stars GO and later
Not Available
| 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.
| A catalogue of Fe/H determinations, 1984 edition
The present version of the Cayrel de Strobel et al. (1981) catalog ofFe/H abundance ratio determinations contains 1921 values for 1035 stars,which represents an augmentation over the previous publication of 48 and47 percent, respectively. In addition, the literature search conductedis complete up to December, 1983. Stellar metal abundance, effectivetemperature, spectroscopic gravity, spectral type, and photometricindices are covered.
| The brightest stars in the Magellanic Clouds and other late-type galaxies
Observational data on the most luminous stars in the Galaxy, theMagellanic Clouds, and other nearby late-type galaxies are compiled intables, characterized, and used to construct a schematic HR diagram.Luminosity calibrations are performed; the position of the S Dor orHubble-Sandage variables on the HR diagram is indicated; and anempirical upper luminosity limit for normal stars, declining withtemperature for the hotter stars but becoming constant for the coolersupergiants, is determined.
| Revised MK Spectral Standard Stars Later than G0
Not Available
| Status of evolution of F, G, and K field stars contained in the Fe/H abundance ratio catalogue
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1983A&A...119....1C&db_key=AST
| The circumstellar envelopes of F- and G-type supergiants in the Large Magellanic Cloud
The outer atmospheres of four F- and G-type supergiants in the LMC arecompared with those of their Milky Way counterparts by means of 2.5 and5.1 A/mm high dispersion Echelle spectra. Na I D line doubling indicatesextensive circumstellar envelopes, mass loss rates greater than 0.00001solar masses/year, and outflow velocities of 10-60 km/sec. The Ca II Hand K lines yield new data on extragalactic star chromospheres.
| High-dispersion spectroscopy of the most luminous F- and G-type supergiants in the Large Magellanic Cloud and the Milky Way
High-resolution spectroscopic observations of the most luminous F- andG-type supergiant stars in the Large Magellanic Cloud and in the Galaxyare compared. High-dispersion echelle spectrograms, at dispersions of2.5 and 5.1 A/mm, were obtained together with optical and infraredphotometry for the four brightest LMC supergiants and seven Galacticsupergiants of comparable spectral types and luminosities. The LMCsupergiants are all observed to exhibit line doubling in the Na I Dlines, while no evidence for circumstellar line cores or line doublingis seen in either Ca I 4226 A or Sr II 4077 A. The galactic yellowsupergiants also show evidence for broad diffuse or doubled lines. TheCa II H and K core emission profiles along with the doubled linesindicate extensive circumstellar envelopes, and lead to estimates ofmass-loss rates in excess of 0.0001 solar mass/year. It is suggestedthat this mass loss rate may be explained by an outer atmosphericstructure consisting of an inner shell in which material circulatesbetween an extended atmosphere and the photosphere, and an outer shellfrom which matter outflow takes place.
| DDO Observations of Southern Stars
Not Available
|
Додај нови чланак
Линкови у сродству са темом
Додај нови линк
Чланови следећих група \:
|
Посматрања и Астрометриски подаци
| Сазвежђа: | Златна риба |
| Ректацензија: | 04h54m14.26s |
| Deклинација: | -69°12'36.5" |
| Apparent магнитуда: | 10.345 |
| Proper motion RA: | -0.1 |
| Proper motion Dec: | -3.4 |
| B-T magnitude: | 12.081 |
| V-T magnitude: | 10.489 |
Каталог и designations:
|
