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Ages and Metallicities of Extragalactic Globular Clusters from Spectral and Photometric Fits of Stellar Population Synthesis Models
Spectra of galaxies contain an enormous amount of information about therelative mixture of ages and metallicities of constituent stars. Wepresent a comprehensive study designed to extract the maximuminformation from spectra of data quality typical in large galaxysurveys. These techniques are not intended for detailed stellarpopulation studies that use high-quality spectra. We test techniques ona sample of globular clusters, which should consist of single stellarpopulations and provide good test cases, using the Bruzual-Charlothigh-resolution stellar population synthesis models to simultaneouslyestimate the ages and metallicities of 101 globular clusters in M31 andthe Magellanic Clouds. The clusters cover a wide range of ages andmetallicities, 4 Myr
| Dust-enshrouded giants in clusters in the Magellanic Clouds
We present the results of an investigation of post-Main Sequence massloss from stars in clusters in the Magellanic Clouds, based around animaging survey in the L'-band (3.8 μm) performed with the VLT at ESO.The data are complemented with JHKs (ESO and 2MASS) andmid-IR photometry (TIMMI2 at ESO, ISOCAM on-board ISO, and data fromIRAS and MSX). The goal is to determine the influence of initialmetallicity and initial mass on the mass loss and evolution during thelatest stages of stellar evolution. Dust-enshrouded giants areidentified by their reddened near-IR colours and thermal-IR dust excessemission. Most of these objects are Asymptotic Giant Branch (AGB) carbonstars in intermediate-age clusters, with progenitor masses between 1.3and ~5 M_ȯ. Red supergiants with circumstellar dust envelopes arefound in young clusters, and have progenitor masses between 13 and 20M_ȯ. Post-AGB objects (e.g., Planetary Nebulae) and massive starswith detached envelopes and/or hot central stars are found in severalclusters. We model the spectral energy distributions of the cluster IRobjects, in order to estimate their bolometric luminosities andmass-loss rates. The IR objects are the most luminous cluster objects,and have luminosities as expected for their initial mass andmetallicity. They experience mass-loss rates in the range from a few10-6 up to 10-4 M_ȯ yr-1 (ormore), with most of the spread being due to evolutionary effects andonly a weak dependence on progenitor mass and/or initial metallicity.About half of the mass lost by 1.3-3 M_ȯ stars is shed during thesuperwind phase, which lasts of order 105 yr. Objects withdetached shells are found to have experienced the highest mass-lossrates, and are therefore interpreted as post-superwind objects. We alsopropose a simple method to measure the cluster mass from L'-band images.
| The Chemical Properties of Milky Way and M31 Globular Clusters. I. A Comparative Study
A comparative analysis is performed between high-quality integratedspectral indices of 30 M31 globular clusters, 20 Milky Way globularclusters, and a sample of field and cluster elliptical galaxies. We findthat the Lick CN indices in the M31 and Galactic clusters are enhancedrelative to the bulges of the Milky Way, M31, and elliptical spheroids,in agreement with Burstein and coworkers. Although not particularlyevident in the Lick CN indices, the near-UV cyanogen feature(λ3883) is strongly enhanced with respect to the Galacticglobular clusters at metallicities -1.5<[Fe/H]<-0.3. Carbon showssigns of varying among these two groups. For [Fe/H]>-0.8, we observeno systematic differences in the Hδ, Hγ, or Hβ indicesbetween the M31 and Galactic globular clusters, in contrast to previousstudies. The elliptical galaxy sample lies offset from the loci of theglobular clusters in both the cyanogen-[MgFe] and Balmer-line-[MgFe]planes. Six of the M31 clusters appear young and are projected onto theM31 disk. Population synthesis models suggest that these are metal-richclusters with ages 100-800 Myr, metallicities -0.20<=[Fe/H]<=0.35,and masses 0.7-~7.0×104 Msolar. Two otheryoung clusters are Hubble V in NGC 205, observed as a template, and anolder (~3 Gyr) cluster some 7 kpc away from the plane of the disk. Thesix clusters projected onto the disk show signs of rotation similar tothe H I gas in M31, and three clusters exhibit thin disk kinematics,according to Morrison and coworkers. Dynamical mass estimates anddetailed structural parameters are required for these objects todetermine whether they are massive open clusters or globular clusters.If they are the latter, our findings suggest globular clusters may tracethe buildup of galaxy disks. In either case, we conclude that theseclusters are part of a young, metal-rich disk cluster system in M31,possibly as young as 1 Gyr old.
| Infrared Surface Brightness Fluctuations of Magellanic Star Clusters
We present surface brightness fluctuations (SBFs) in the near-IR for 191Magellanic star clusters available in the Second Incremental and All SkyData releases of the Two Micron All Sky Survey (2MASS) and compare themwith SBFs of Fornax Cluster galaxies and with predictions from stellarpopulation models as well. We also construct color-magnitude diagrams(CMDs) for these clusters using the 2MASS Point Source Catalog (PSC).Our goals are twofold. The first is to provide an empirical calibrationof near-IR SBFs, given that existing stellar population synthesis modelsare particularly discrepant in the near-IR. Second, whereas mostprevious SBF studies have focused on old, metal-rich populations, thisis the first application to a system with such a wide range of ages(~106 to more than 1010 yr, i.e., 4 orders ofmagnitude), at the same time that the clusters have a very narrow rangeof metallicities (Z~0.0006-0.01, i.e., 1 order of magnitude only). Sincestellar population synthesis models predict a more complex sensitivityof SBFs to metallicity and age in the near-IR than in the optical, thisanalysis offers a unique way of disentangling the effects of age andmetallicity. We find a satisfactory agreement between models and data.We also confirm that near-IR fluctuations and fluctuation colors aremostly driven by age in the Magellanic cluster populations and that inthis respect they constitute a sequence in which the Fornax Clustergalaxies fit adequately. Fluctuations are powered by red supergiantswith high-mass precursors in young populations and by intermediate-massstars populating the asymptotic giant branch in intermediate-agepopulations. For old populations, the trend with age of both fluctuationmagnitudes and colors can be explained straightforwardly by evolution inthe structure and morphology of the red giant branch. Moreover,fluctuation colors display a tendency to redden with age that can befitted by a straight line. For the star clusters only,(H-Ks)=(0.21+/-0.03)log(age)-(1.29+/-0.22) once galaxies areincluded, (H-Ks)=(0.20+/-0.02)log(age)-(1.25+/-0.16).Finally, we use for the first time a Poissonian approach to establishthe error bars of fluctuation measurements, instead of the customaryMonte Carlo simulations.This research has made use of the NASA/ IPAC Infrared Science Archive,which is operated by the Jet Propulsion Laboratory, California Instituteof Technology, under contract with the National Aeronautics and SpaceAdministration.
| A Revised and Extended Catalog of Magellanic System Clusters, Associations, and Emission Nebulae. II. The Large Magellanic Cloud
A survey of extended objects in the Large Magellanic Cloud was carriedout on the ESO/SERC R and J Sky Survey Atlases, checking entries inprevious catalogs and searching for new objects. The census provided6659 objects including star clusters, emission-free associations, andobjects related to emission nebulae. Each of these classes containsthree subclasses with intermediate properties, which are used to infertotal populations. The survey includes cross identifications amongcatalogs, and we present 3246 new objects. We provide accuratepositions, classification, and homogeneous measurements of sizes andposition angles, as well as information on cluster pairs andhierarchical relation for superimposed objects. This unification andenlargement of catalogs is important for future searches of fainter andsmaller new objects. We discuss the angular and size distributions ofthe objects of the different classes. The angular distributions show twooff-centered systems with different inclinations, suggesting that theLMC disk is warped. The present catalog together with its previouscounterpart for the SMC and the inter-Cloud region provide a totalpopulation of 7847 extended objects in the Magellanic System. Theangular distribution of the ensemble reveals important clues on theinteraction between the LMC and SMC.
| The evolution of theV-Kcolours of single stellar populations
Models of evolutionary population synthesis of galaxies rely on theproperties of the so-called single stellar populations (SSP). In thispaper, we discuss how the integrated near-infrared colours, andespecially V-K, of SSPs evolve with age and metallicity. Some of theuncertainties associated with the properties of the underlying stellarmodels are thoroughly discussed. Our models include all the relevantstellar evolutionary phases, with particular attention being dedicatedto the asymptotic giant branch (AGB), which plays a fundamental role inthe evolution of the near-infrared part of the spectrum. First, wepresent the effects that different formulations for the mass-loss ratesproduce on the final remnant mass (i.e., on the initial-final massrelation), and hence on the AGB-termination luminosity and the relativecontribution of these stars to the integrated light. The results for theevolution of the V-K colour are very different depending on the choiceof the mass-loss prescription; the same is true also for the B-V colourin the case of low-metallicity SSPs. Secondly, we describe the changesoccurring in the integrated colours at the onset of the AGB and redgiant (RGB) branches. According to the classical formalism for the AGBevolution, the onset of this evolutionary phase is marked by a colourjump to the red, the amplitude of which is shown here to be highlydependent on the metallicity and mass-loss rates adopted in the models.We then consider the effect of the overluminosity with respect to thestandard core mass-luminosity relation that occurs in the most massiveAGB stars. Different simplified formulations for this effect are testedin the models; they cause a smoothing of the colour evolution in the agerange at which the AGB starts to develop, rather than a splitting of thecolour jump into two separate events. On the other hand, we find that atemporary red phase takes place ~1.5x10^8 yr after the RGB develops.Thanks to the transient nature of this feature, the onset of the RGB isprobably not able to cause marked features in the spectral evolution ofgalaxies. We then discuss the possible reasons for the transition of V-Kcolours (from ~1.5 to 3) that takes place in LMC clusters of SWB typeIV. A revision of the ages attributed to the single clusters revealsthat the transition may not be as fast as originally suggested. Thecomparison of the data with the models indicates that the transitionresults mainly from the development of the AGB. A gradual (or delayed)transition of the colours, as predicted by models which include theoverluminosity of the most massive AGB stars, seems to describe the databetter than the sudden colour jump predicted by classical models.
| Recent Star Formation in Shapley Constellation III in the Large Magellanic Cloud
We present UBV photometry of four fields within Shapley ConstellationIII and one field on the edge of the shell. Our fields cover roughly 20%of the region, mostly in the southern half. Determinations are made ofages of the fields, the star formation densities, and the initial massfunction (IMF) slopes. The field-age determinations inside theconstellation show ages between 12 and 16 Myr uncorrelated with distancefrom the center, while the age of the field on the edge of theconstellation shows an age of around 6-7 Myr. The southern part of theconstellation shows star formation densities and IMF slopes typical ofOB associations and giant H ii regions, while the northern part showssignificantly fewer intermediate-mass stars and a steeper IMF slope. Wecompare these properties of Constellation III with those of 30 Doradus,another LMC star-forming region of comparable size to Constellation III.Although the regions formed from roughly the same amount of gas, weestimate that 30 Doradus formed a few times more stars thanConstellation III.
| Constraints on the initial conditions of globular clusters
N-body simulations are made with a variety of initial conditions, inparticular clumpy and flattened distributions, to attempt to constrainthe possible initial conditions of globular clusters, using theobservations that young LMC globular clusters appear relaxed after only20 to 40 Myr. It is found that violent relaxation is able to erase mostof the initial substructure in only approximately six crossing times.However, initially very clumpy distributions (not greater than about 100clumps) form clusters that are too concentrated to resemble realglobular clusters. Such clusters also often have large clumps inlong-lasting (not less than about 30 crossing times) orbits which do notappear in observed cluster profiles. It is also found that even modestamounts of initial flattening produce clusters that are too ellipticalto resemble real globular clusters. In such a scenario, cloud-cloudcollisions and similar energetic processes would be unlikely to producesufficiently spherical globular clusters. It is suggested that globularclusters form from roughly spherical initial conditions with starformation occurring either smoothly or in many small clumps.
| Young red supergiants and the near-infrared light appearance of disk galaxies
We have searched for spatial variations in the 2.3 m photometric COindex within the disks of three nearby galaxies. This index measures thestrength of the absorption bands of molecular CO in stellar atmospheresand is strong in cool, low surface gravity stars, reaching the largestvalues for red supergiants. We observe significant spatial CO indexvariations in two galaxies, indicating that the dominant stellarpopulation in the NIR is not everywhere the same. Central CO index peaksare present in two galaxies; these could be due to either metallicitygradients or to recent star formation activity. In addition, significantazimuthal CO index variations are observed in one. Because strongazimuthal metallicity gradients are physically implausible in diskgalaxies, these features are most naturally explained by the presence ofa young stellar population. The fraction of 2 m light due to youngstellar populations in star-forming regions can be calculated from ourdata. Overall, young stellar populations can contribute 3 percent of theNIR flux of a (normal) galaxy, which is consistent with other globalproperties. Locally, this fraction may rise to 33 percent. Thus, youngstars do not dominate the total NIR flux, but can be locally dominant instar-forming regions, and can bias estimates of spiral arm amplitude orother nonaxisymmetric structures in galaxies' mass distributions.
| Mid-infrared properties of globular clusters using the IRAS data base
We present an analysis of the mid-IR properties of 18 globular clusters(GCs) [15 in the Galaxy and three in the Large Magellanic Cloud (LMC)]using the IRAS photometric data at 12 and 25 mum. Eight of the nineGalactic GCs with central escape velocities greater than 50 km s^-1 haveIRAS sources within a radius of 60 arcsec from the centre, in agreementwith the expectation that interstellar gas and dust should indeed bepresent in the central regions of the most massive clusters owing tomass-loss processes occurring in the late stages of the stellarevolution. No other significant correlation is found between IRAS sourceincidence and any intrinsic GC parameters. Warm dust (T~300K) isdetectable mostly around unresolved giant stars, but in three massiveGCs it is also present as diffuse emission. However, most of the dustmight be cold (T<50K) and it was thus notdetected by IRAS because of its limited sensitivity at 60 and 100 mum.The inferred mass-loss rates and statistical considerations arecompatible with a non-steady mass-loss process with several episodes ofejection lasting a few times 10^5 yr.
| Integrated UBV Photometry of 624 Star Clusters and Associations in the Large Magellanic Cloud
We present a catalog of integrated UBV photometry of 504 star clustersand 120 stellar associations in the LMC, part of them still embedded inemitting gas. We study age groups in terms of equivalent SWB typesderived from the (U-B) X (B-V) diagram. The size of the spatialdistributions increases steadily with age (SWB types), whereas adifference of axial ratio exists between the groups younger than 30 Myrand those older, which implies a nearly face-on orientation for theformer and a tilt of ~45^deg^ for the latter groups. Asymmetries arepresent in the spatial distributions, which, together with thenoncoincidence of the centroids for different age groups, suggest thatthe LMC disk was severely perturbed in the past.
| Blue-violet spectral evolution of young Magellanic Cloud clusters
We study the integrated spectral evolution in the blue-violet range of97 blue star clusters in the Magellanic Clouds, from those associatedwith gas emission to those as old as a few hundred Myr. Some clustersare dominated by the flux of those massive stars that pass throughevolutionary stages such as Wolf-Rayet, Luminous Blue Variable, Be, andsupergiant stars of different temperatures. The relationships amongspectral features such as absorption and emission lines, Balmerdiscontinuity and Balmer continuum are used to study the spectralevolution of the clusters. Finally, we sort into groups spectra ofsimilar evolutionary stages, creating a template spectral library withpossible applications in stellar populations syntheses of star-forminggalaxies and in the spectral simulation of bursts of star formation withdifferent mean ages and durations.
| A radio continuum study of the Magellanic Clouds. IV. Catalogues of radio sources in the Large Magellanic Cloud at 1.40, 2.45, 4.75, 4.85 and 8.55 GHz.
From observations with the Parkes radio telescope, we present cataloguesof radio sources in the Large Magellanic Cloud at four frequencies:1.40, 2.45, 4.75 and 8.55GHz, and an additional catalogue from a sourceanalysis of the Parkes-MIT-NRAO survey at 4.85GHz. A total of 469sources have been detected at least one of these frequencies, 132 ofwhich are reported here for the first time as radio sources.
| Colour Evolution Models and the Distribution of Large Magellanic Cloud Clusters in the Integrated UBV Plane
We present a comparison between photometric cluster models, based onclassical and with-overshooting stellar tracks, and the enlarged sampleof 624 LMC clusters recently gathered in integrated UBV photometry byBica et al. Models based on Maeder and Meynet's tracks present twotemporary red phases: the first at age 10 Myr, caused by a clump of redsupergiants; the second at ~100 Myr due to the combined effect of boththe progressive reduction of the blue loop of core He-burning stars, andtheir fading relative to top-MS stars. The 100 Myr red phase does notoccur in models without overshooting. Taking into account stochasticeffects on the mass distribution of stars, the models describe well thegeneral distribution of clusters in the (U - B) vs. (B - V) diagram,except for the oldest, SWB types V-VII, clusters. The dispersion ofcluster colours due to stochastic effects is found to be stronglyvariable along the ageing sequence: the general trend is a decrease withage due to the increasing population of post-MS phases, but thedispersion increases in the temporary red phases and is expected toincrease again after the red giant branch phase transition due to theappearance of extended RGBs and carbon stars. We also study the LMCclusters age distribution function, based on the age frequency ofclusters of equal initial masses, taking into account different valuesfor the IMF slope.
| The structure and evolution of rich star clusters in the Large Magellanic Cloud
The present evaluation of surface brightness profiles andcolor-magnitude diagrams for 18 rich star clusters in the LMC, whoseages range from 10 million to 1 billion years, notes that while theprofiles of the older clusters are representable by models withKing-like cores, those of many younger clusters resist such modeling invirtue of bumps, sharp 'shoulders', and central dips. If the clustershave undergone violent relaxation, then the small cores of the youngestones may be indicative of formation from relatively 'cool' initialconditions. The sharp shoulders would then point point toward 'warmer'initial conditions, although they are alternatively explainable assignatures of merging subcondensations.
| Near-infrared spectral evolution of blue LMC clusters : a comparison with galactic open clusters.
Abstract image available at:http://adsabs.harvard.edu/abs/1990RMxAA..21..202B
| The cluster system of the Large Magellanic Cloud
A new catalog of clusters in the Large Magellanic Cloud has beenconstructed from searches of the IIIa-J component of the ESO/SERCSouthern Sky Atlas. The catalog contains coordinate and diametermeasurements of 1762 clusters in a 25 deg x 25 deg area of sky centeredon the LMC, but excluding the very crowded 3.5 sq deg region around theBar. The distribution of these clusters appears as two superimposedelliptical systems. The higher density inner system extends over about 8deg; the lower density outer system can be represented by a 13 deg x 10deg disk inclined at 42 deg to the line of sight. There are suggestionsof two weak 'arms' in the latter.
| Blue Magellanic clusters - Near-infrared spectral evolution
New integrated spectra in the range 5600-10,000 A are presented for 28LMC and 3 SMC young star clusters. The equivalent widths (W) ofprominent features and the continuum distribution are measured. Theanalysis, supplemented by 8 additional LMC clusters from previousstudies, indicates that the red supergiant phase is indeed verytime-peaked, occuring from 7 to 12 Myr. In addition to the previous caseof NGC 2004, it is found that NGC 1805, NGC 1994, NGC 2002, NGC 2098,and NGC 2100 (as well as NGC 2011 to a lesser extent) are undergoingthis phase. The red supergiant phase is clearly denoted by strong TiObands and Ca II triplet as well as a flat continuum or (in extremecases) a continuum with positive slope above 6000 A.
| Core expansion in young star clusters in the Large Magellanic Cloud
The core radii of 18 rich star clusters in the LMC with ages from 10 Myrto 1 Gyr. Data for an additional 17 clusters with ages from 1 Myr to 10Gyr are available in the literature. The combined sample shows that thecore radii increase from about 0 to about 5 pc between about 1 Myr and 1Gyr, and then begin to decrease again. The expansion of the cores isprobably driven by mass loss from evolving stars. Models of clusterevolution show that the rate of increase in core radius is sensitive tothe slope of the initial mass function. The observed core radius-agerelation for the LMC clusters favors an intial mass function with slopeslightly flatter than the Salpeter value.
| Integrated UV magnitudes of the Large Magellanic Cloud associations
UV photographs (2600 A, 350 A passband) of the LMC have been obtained bythe S183 experiment during a Skylab mission. The background is estimatedand a method for deriving the integrated fluxes is presented. Theintegrated magnitudes of about 50 associations and isocontours of theirintensities are given, along with the B and V integrated magnitudes of13 associations.
| The stellar populations of Shapley constellation III
A V-I color-magnitude diagram is presented for a 0.6-sq deg fieldencompassing part of the LMC's Shapley III star-formation region. Thepronounced luminosity function peak exhibited by the main-sequence starsis identified with the turnoff of the first star-forming burst, and thenused as an age indicator with which to compare stellar evolutionarymodels with the dynamical age estimate determined by Dopita et al.(1985); the initial luminosity and mass functions are derived. Thedynamical clock in Shapley III is in better agreement with the stellarevolutionary clock if models without convective overshoot are adopted.
| A preliminary survey of collapsed cores in the Magellanic Clouds' globular clusters
A preliminary report on a surface photometry survey for collapsed coresin the Magellanic Clouds' globular clusters is presented. Coremorphology classifications are given for the 33 globular clustersexamined so far. One cluster, NGC 2019, shows definite signs of acollapsed core, and two others, NGC 1774 and NGC 1951, appear as strongcandidates. This detection of postcollapse cores outside the Milky Wayopens some interesting prospects for future dynamical studies. However,the fraction of collapsed-core clusters appears to be smaller in theMagellanic Clouds than in the Galaxy. This may be due in part to theiryounger ages, or to the limitations imposed by the seeing effects. It isalso possible that the relative scarcity reflects the physicaldifference in the tidal field environments between the Galaxy and theClouds, in agreement with a trend found earlier, viz., that the tidalshocks from disk passages accelerate dynamical evolution and enhance thepropensity for core collapse.
| Age calibration and age distribution for rich star clusters in the Large Magellanic Cloud
An empirical relation is presented for estimating the ages of rich starclusters in the Large Magellanic Cloud (LMC), to within a factor ofabout 2, from their integrated UBV colors. The calibration is based onpublished ages for 58 LMC clusters derived from main-sequencephotometry, integrated spectra, or the extent of the asymptotic giantbranches. Using stellar population models, a sample of LMC clusters moremassive than about 10,000 solar masses is isolated, which is correctedfor incompleteness as a function of magnitude. An unbiased agedistribution for three clusters is then determined. The number ofclusters decreases with increasing age in a manner that is qualitativelysimilar to the age distribution for the open clusters in our Galaxy. TheLMC age distribution is, however, flatter, and the median age of theclusters is greater. If the formation rate has been approximatelyconstant over the history of the two galaxies, then the age distributionobtained here implies that clusters are disrupted more slowly in theLMC. The results contain no evidence for bursts in the formation ofclusters, although fluctuations on small time scales and slow variationsover the lifetime of the LMC cannot be ruled out.
| The Identifications of HDE Objects with Large Magellanic Cloud Clusters and Nebulae
Not Available
| 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.
| The Identification of Large Magellanic Cloud Star Clusters in DM Catalogues
Not Available
| The brightest stars as extragalactic distance indicators
The luminosities of the brightest blue and red supergiants werecalibrated by the spectra and photometry of such stars in six LocalGroup galaxies. It is found that the brightest blue supergiants are allA type supergiants, their luminosities depending strongly on theluminosity of the parent galaxy. The same relationship obtains for themost luminous (bolometric) stars in the galaxies. It is also found thatthere is a tight upper limit to the visual luminosities of the Msupergiants at -8.0 + or - 0.2 mag in spiral and irregular type galaxiescovering almost 6 mag of galactic luminosity from -20.5 to -14.8 mag. Itis concluded that the M supergiants are excellent extragalactic distanceindicators for spiral and Magellanic type irregular galaxies andprobably also for the less luminous dwarf irregular galaxies.
| Photometric studies of composite stellar systems. V - Infrared photometry of star clusters in the Magellanic clouds
Abstract image available at:http://adsabs.harvard.edu/abs/1983ApJ...266..105P
| Studies of luminous stars in nearby galaxies. II - M supergiants in the Large Magellanic Cloud
Basic properties of the brightest red stars in the Large MagellanicCloud (LMC) are determined from BVRI photometry of 157 red stars andspectra of 74 of the brightest red stars, including 54 confirmedsupergiants. The luminosities, reddening, and colors of the Msupergiants are obtained. H-R diagrams for the luminous stars of allspectral types in the LMC are provided, and general features of thesediagrams are examined. The ratio of blue to red supergiants in the LMCis estimated to be 5 for distances of no more than 1 kpc from thecenter, 3.5 for distances of 1 to 2 kpc, 3.8 for distances of 2 to 3kpc, and 2.3 for distances of at least 3 kpc. It is shown that theluminous red stars in the LMC and the Galaxy have essentially the samespectral characteristics and luminosities.
| 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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