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On the Formation of Perseus OB1 at High Galactic Latitudes
The Per OB1 association, which contains the remarkable double cluster hand χ Per, is unusual in not having a giant molecular cloud in itsvicinity. We show from Hipparcos data that the luminous members of thisassociation exhibit a bulk motion away from the Galactic plane, suchthat their average velocity increases with height above the Galacticplane. We find HAeBe and T Tauri stars toward probable remnant molecularclouds associated with Per OB1. These star-forming regions lie wellbeyond the location of the luminous member stars at heights of 280-400pc above the Galactic plane, far higher than that previously found forembedded clusters. We argue that the observed motion of the luminousmember stars is most naturally explained if many formed from moleculargas pushed and accelerated outward by an expanding superbubble, drivenpresumably by stellar winds and perhaps also by supernova explosions. Alarge shell of atomic hydrogen gas and dust that lies just beyond theremnant molecular clouds, believed to be driven by just such asuperbubble, may comprise the swept-up remains of the parental giantmolecular cloud from which this association formed. In support of thispicture, we find a weak trend for the younger O star members to lie athigher Galactic latitudes than the older supergiant members. Thestar-forming regions located at even larger heights above the Galacticplane presumably correspond to more recent episodes of star formation ator near the periphery of this superbubble.
| A New VLA-Hipparcos Distance to Betelgeuse and its Implications
The distance to the M supergiant Betelgeuse is poorly known, with theHipparcos parallax having a significant uncertainty. For detailednumerical studies of M supergiant atmospheres and winds, accuratedistances are a prerequisite to obtaining reliable estimates for manystellar parameters. New high spatial resolution, multiwavelength,NRAO33The National Radio Astronomy Observatory is a facilityof the National Science Foundation operated under cooperative agreementby Associated Universities, Inc. Very Large Array (VLA) radio positionsof Betelgeuse have been obtained and then combined with HipparcosCatalogue Intermediate Astrometric Data to derive new astrometricsolutions. These new solutions indicate a smaller parallax, and hencegreater distance (197 +/- 45 pc), than that given in the originalHipparcos Catalogue (131 +/- 30 pc) and in the revised Hipparcosreduction. They also confirm smaller proper motions in both rightascension and declination, as found by previous radio observations. Weexamine the consequences of the revised astrometric solution onBetelgeuse's interaction with its local environment, on its stellarproperties, and its kinematics. We find that the most likelystar-formation scenario for Betelgeuse is that it is a runaway star fromthe Ori OB1 association and was originally a member of a high-massmultiple system within Ori OB1a.
| The Long-Term Behavior of the Semiregular M Supergiant Variable BC Cygni
The long-term brightness changes in the M supergiant, type C semiregularvariable, Type II supernova progenitor BC Cyg from 1890 to the presentare examined using archival data obtained from photographic plates inthe collections of Harvard College Observatory and SternbergAstronomical Institute, in conjunction with AAVSO observations. BC Cygpulsates with a period close to 700 days but underwent a 0.5 magincrease in brightness between 1900 and 2000, in conjunction with adecrease in pulsation period from 699 to 687 days. Such changes appearto be evolutionary in origin, representing a small contraction of thestar associated with a slight decrease in luminosity. Its evolutionarymass is estimated to be ~19 Msolar from its membership inBerkeley 87, a feature that also permits it to be used to test the Msupergiant period-luminosity relation.
| Variability in red supergiant stars: pulsations, long secondary periods and convection noise
We study the brightness variations of galactic red supergiant starsusing long-term visual light curves collected by the AmericanAssociation of Variable Star Observers over the last century. The fullsample contains 48 red semiregular or irregular variable stars, with amean time-span of observations of 61 yr. We determine periods and periodvariability from analyses of power density spectra and time-frequencydistributions. We find two significant periods in 18 stars. Most ofthese periods fall into two distinct groups, ranging from a few hundredto a few thousand days. Theoretical models imply fundamental, first andpossibly second overtone mode pulsations for the shorter periods.Periods greater than 1000 d form a parallel period-luminosity relationthat is similar to the long secondary periods of the asymptotic giantbranch stars. A number of individual power spectra shows a single moderesolved into multiple peaks under a Lorentzian envelope, which weinterpret as evidence for stochastic oscillations, presumably caused bythe interplay of convection and pulsations. We find a strong 1/f noisecomponent in the power spectra that is remarkably similar in almost allstars of the sample. This behaviour fits the picture of irregularphotometric variability caused by large convection cells, analogous tothe granulation background seen in the Sun.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| Project Jelly-Fish: B.R.N.O. Observations of Semiregular Variable Stars
Brno Regional Network of Observers (BRNO) is a group which prefers toobserve eclipsing binary stars. A team called the Jelly-Fish has beenformed within BRNO for the purpose of observing variable stars otherthan eclipsing binaries. The observations by Jelly-Fish members arepredominantly visual; CCD observing has started only recently and suchobservations are not yet included in our statistics. Jelly-Fish hasabout twenty members at this moment. This paper presents preliminaryresults based on Jelly-Fish observations of S Camelopardalis, AUCamelopardalis, WZ Cassiopeiae, RS Cygni, T Persei, RU Persei, and RUrsae Minoris.
| Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters
The availability of the Hipparcos Catalogue has triggered many kinematicand dynamical studies of the solar neighbourhood. Nevertheless, thosestudies generally lacked the third component of the space velocities,i.e., the radial velocities. This work presents the kinematic analysisof 5952 K and 739 M giants in the solar neighbourhood which includes forthe first time radial velocity data from a large survey performed withthe CORAVEL spectrovelocimeter. It also uses proper motions from theTycho-2 catalogue, which are expected to be more accurate than theHipparcos ones. An important by-product of this study is the observedfraction of only 5.7% of spectroscopic binaries among M giants ascompared to 13.7% for K giants. After excluding the binaries for whichno center-of-mass velocity could be estimated, 5311 K and 719 M giantsremain in the final sample. The UV-plane constructed from these datafor the stars with precise parallaxes (σπ/π≤20%) reveals a rich small-scale structure, with several clumpscorresponding to the Hercules stream, the Sirius moving group, and theHyades and Pleiades superclusters. A maximum-likelihood method, based ona Bayesian approach, has been applied to the data, in order to make fulluse of all the available stars (not only those with precise parallaxes)and to derive the kinematic properties of these subgroups. Isochrones inthe Hertzsprung-Russell diagram reveal a very wide range of ages forstars belonging to these groups. These groups are most probably relatedto the dynamical perturbation by transient spiral waves (as recentlymodelled by De Simone et al. \cite{Simone2004}) rather than to clusterremnants. A possible explanation for the presence of younggroup/clusters in the same area of the UV-plane is that they have beenput there by the spiral wave associated with their formation, while thekinematics of the older stars of our sample has also been disturbed bythe same wave. The emerging picture is thus one of dynamical streamspervading the solar neighbourhood and travelling in the Galaxy withsimilar space velocities. The term dynamical stream is more appropriatethan the traditional term supercluster since it involves stars ofdifferent ages, not born at the same place nor at the same time. Theposition of those streams in the UV-plane is responsible for the vertexdeviation of 16.2o ± 5.6o for the wholesample. Our study suggests that the vertex deviation for youngerpopulations could have the same dynamical origin. The underlyingvelocity ellipsoid, extracted by the maximum-likelihood method afterremoval of the streams, is not centered on the value commonly acceptedfor the radial antisolar motion: it is centered on < U > =-2.78±1.07 km s-1. However, the full data set(including the various streams) does yield the usual value for theradial solar motion, when properly accounting for the biases inherent tothis kind of analysis (namely, < U > = -10.25±0.15 kms-1). This discrepancy clearly raises the essential questionof how to derive the solar motion in the presence of dynamicalperturbations altering the kinematics of the solar neighbourhood: doesthere exist in the solar neighbourhood a subset of stars having no netradial motion which can be used as a reference against which to measurethe solar motion?Based on observations performed at the Swiss 1m-telescope at OHP,France, and on data from the ESA Hipparcos astrometry satellite.Full Table \ref{taba1} is only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/430/165}
| Brightness and Polarization Variations of S Per and T Per
Results of photoelectric BV observations of the brightness andpolarization in the V band for S Per and T Per over a period of eightyears are presented. An attempt is made to isolate the interstellarpolarization. A comparison of the variations in the brightness andintrinsic polarization reveals some relationships among thesequantities.
| Observations of Star-Forming Regions with the Midcourse Space Experiment
We have imaged seven nearby star-forming regions, the Rosette Nebula,the Orion Nebula, W3, the Pleiades, G300.2-16.8, S263, and G159.6-18.5,with the Spatial Infrared Imaging Telescope on the Midcourse SpaceExperiment (MSX) satellite at 18" resolution at 8.3, 12.1, 14.7, and21.3 μm. The large angular scale of the regions imaged (~7.2-50deg2) makes these data unique in terms of the combination ofsize and resolution. In addition to the star-forming regions, twocirrus-free fields (MSXBG 160 and MSXBG 161) and a field near the southGalactic pole (MSXBG 239) were also imaged. Point sources have beenextracted from each region, resulting in the identification over 500 newsources (i.e., no identified counterparts at other wavelengths), as wellas over 1300 with prior identifications. The extended emission from thestar-forming regions is described, and prominent structures areidentified, particularly in W3 and Orion. The Rosette Nebula isdiscussed in detail. The bulk of the mid-infrared emission is consistentwith that of photon-dominated regions, including the elephant trunkcomplex. The central clump, however, and a line of site toward thenorthern edge of the cavity show significantly redder colors than therest of the Rosette complex.
| The association of IRAS sources and 12CO emission in the outer Galaxy
We have revisited the question of the association of CO emission withIRAS sources in the outer Galaxy using data from the FCRAO Outer GalaxySurvey (OGS). The availability of a large-scale high-resolution COsurvey allows us to approach the question of IRAS-CO associations from anew direction - namely we examined all of the IRAS sources within theOGS region for associated molecular material. By investigating theassociation of molecular material with random lines of sight in the OGSregion we were able to construct a quantitative means to judge thelikelihood that any given IRAS-CO association is valid and todisentangle multiple emission components along the line of sight. Thepaper presents a list of all of the IRAS-CO associations in the OGSregion. We show that, within the OGS region, there is a significantincrease ( ~ 22%) in the number of probable star forming regions overprevious targeted CO surveys towards IRAS sources. As a demonstration ofthe utility of the IRAS-CO association table we present the results ofthree brief studies on candidate zone-of-avoidance galaxies with IRAScounterparts, far outer Galaxy CO clouds, and very bright CO clouds withno associated IRAS sources. We find that ~ 25% of such candidate ZOAGsare Galactic objects. We have discovered two new far outer Galaxystar-forming regions, and have discovered six bright molecular cloudsthat we believe are ideal targets for the investigation of the earlieststages of sequential star formation around HII regions. Finally, thispaper provides readers with the necessary data to compare othercatalogued data sets with the OGS data.Tables 1, 2 and A1 are only available in electronic form at the CDS viaanonymous ftp to\ cdsarc.u-strasbg.fr (130.79.128.5) or via\http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/399/1083
| Hipparcos red stars in the HpV_T2 and V I_C systems
For Hipparcos M, S, and C spectral type stars, we provide calibratedinstantaneous (epoch) Cousins V - I color indices using newly derivedHpV_T2 photometry. Three new sets of ground-based Cousins V I data havebeen obtained for more than 170 carbon and red M giants. These datasetsin combination with the published sources of V I photometry served toobtain the calibration curves linking Hipparcos/Tycho Hp-V_T2 with theCousins V - I index. In total, 321 carbon stars and 4464 M- and S-typestars have new V - I indices. The standard error of the mean V - I isabout 0.1 mag or better down to Hp~9 although it deteriorates rapidly atfainter magnitudes. These V - I indices can be used to verify thepublished Hipparcos V - I color indices. Thus, we have identified ahandful of new cases where, instead of the real target, a random fieldstar has been observed. A considerable fraction of the DMSA/C and DMSA/Vsolutions for red stars appear not to be warranted. Most likely suchspurious solutions may originate from usage of a heavily biased color inthe astrometric processing.Based on observations from the Hipparcos astrometric satellite operatedby the European Space Agency (ESA 1997).}\fnmsep\thanks{Table 7 is onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/397/997
| High Angular Resolution Observations of Late-Type Stars
This paper presents speckle observations of Mira (o Cet) and late-typestars with the PISCO speckle camera of Pic du Midi during the period1995-1998. A survey for binarity among a sample of late-type stars wasperformed, which led to seven positive detections out of 36 objects.Photometric and color variations of the companion of Mira were searchedfor, but no significant brightness variations could be found over atimescale of ~5-10 minutes. The position and photometry measurements,the restored images with high angular resolution of the binary systemMira A-B (ADS 1778) are in full agreement with Hubble Space Telescopedata obtained at the same epoch. A new orbit has been derived for MiraA-B.
| Long period variable stars: galactic populations and infrared luminosity calibrations
In this paper HIPPARCOS astrometric and kinematic data are used tocalibrate both infrared luminosities and kinematical parameters of LongPeriod Variable stars (LPVs). Individual absolute K and IRAS 12 and 25luminosities of 800 LPVs are determined and made available in electronicform. The estimated mean kinematics is analyzed in terms of galacticpopulations. LPVs are found to belong to galactic populations rangingfrom the thin disk to the extended disk. An age range and a lower limitof the initial mass is given for stars of each population. A differenceof 1.3 mag in K for the upper limit of the Asymptotic Giant Branch isfound between the disk and old disk galactic populations, confirming itsdependence on the mass in the main sequence. LPVs with a thin envelopeare distinguished using the estimated mean IRAS luminosities. The levelof attraction (in the classification sense) of each group for the usualclassifying parameters of LPVs (variability and spectral types) isexamined. Table only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/374/968 or via ASTRIDdatabase (http://astrid.graal.univ-montp2.fr).
| Aufsuchkarten fur intrinsic Variable Stars in Brno.
Not Available
| Dust features in the 10-mu m infrared spectra of oxygen-rich evolved stars
We have analyzed the 8-13.5 mu m UKIRT CGS3 spectra of 142 M-type starsincluding 80 oxygen-rich AGB stars and 62 red supergiants, with a viewto understanding the differences and similarities between the dustfeatures of these stars. We have classified the spectra into groupsaccording to the observed appearance of the infrared features. In eachcase the normalized continuum-subtracted spectrum has been compared tothose of the other stars to find similarities and form groups. The dustfeatures of the AGB stars are classified into six groups: broad AGB,where the feature extends from 8 mu m to about 12.5 mu m with littlestructure; broad+sil AGB, which consists of a broad feature with anemerging 9.7 mu m silicate bump; and four silicate AGB groups in which a``classic'' 9.7 mu m silicate feature gets progressively narrower.Likewise, the supergiant spectra have also been classified into groups,however these do not all coincide with the AGB star groups. In thesupergiant case we again have six groups: featureless, where there islittle or no emission above the continuum; broad Super, where thefeature extends from about 9 mu m to about 13 mu m; and four silicateSuper groups, which again show a progression towards the narrowest``classic'' 9.7 mu m silicate feature. We compare the mean spectrum foreach group, which yields two main results. Firstly, while the``classic'' silicate feature is essentially identical for both AGB starsand red supergiants, the broad features observed for these two stellartypes are quite different. We suggest that the dust in these twoenvironments follows different evolutionary paths, with the dust aroundMira stars, whose broad feature spectra can be fit by a combination ofalumina (Al2O3) and magnesium silicate,progressing from this composition to dust dominated by magnesiumsilicate only, while the dust around supergiants, whose broad featurecan be fit by a combination of Ca-Al-rich silicate andAl2O3, progresses from this initial composition toone eventually also dominated by magnesium silicate. The reason for thedifference in the respective broad features is not clear as yet, butcould be influenced by lower C/O ratios and chromospheric UV radiationfields in supergiant outflow environments. The second result concernsthe 12.5 - 13.0 mu m feature discovered in IRAS LRS spectra and widelyattributed to Al2O3. This feature is seenpredominantly in the spectra of semiregular variables, sometime in Mirasand only once (so far) in supergiant spectra. We argue that it isunlikely that this feature is due to Al2O3 or, ashas more recently been suggested, spinel(MgAl2O4), but could be associated with silicondioxide or highly polymerized silicates (not pyroxenes or olivines).
| Observational investigation of mass loss of M supergiants
We present the analysis of infrared photometry and millimeterspectroscopy of a sample of 74 late-type supergiants. These observationsare particularly suitable to study the mass loss and the circumstellarenvelopes of evolved massive stars. In particular, we quantify thecircumstellar infrared excess, the relation of mass loss with stellarproperties, using the K-[12] colour index as mass-loss indicator. We donot find any clear correlation between mass loss rate and luminosity. Wealso show that the K-band magnitude is a simple luminosity indicator,because of the relative constancy of the K-band bolometric correction.Based on observations collected at the European Southern Observatory, LaSilla, Chile within program ESO 54.E-0914, and on observations collectedwith the IRAM 30m telescope. Tables A1 to A3 are only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html
| Period-luminosity relations for red supergiant variables - I.The calibration
We present CCD photometry of red supergiant long-period variables (LPVs)in the Per OB1 association, the Large Magellanic Cloud (LMC) and M33.The photometry was obtained in the Kron-Cousins R and I bandpasses andin a narrow bandpass (λ0=8250Å, FWHM=300Å)chosen to avoid TiO bands in the spectral energy distribution of theLPVs. Because the strength of the TiO bands varies greatly withtemperature, which varies with the phase of an LPV, avoiding TiO reducesthe amplitude of the photometric variations seen in LPVs. The result isa lower dispersion and a well defined period-luminosity (PL) relation.For the LMC sample we find an rms dispersion of 0.27mag in thenarrow-band PL relation and slightly larger dispersions for the LPVs inPer OB1 and M33. This dispersion is comparable to that of the Cepheid PLrelation at similar wavelengths. Adopting a distance modulus of18.5+/-0.1mag for the LMC, we obtain distance moduli of 11.68+/-0.15magfor Per OB1 and 24.85+/-0.13mag for M33. These distances agree well withthose based on main sequence fitting for Per OB1 and the Cepheiddistance for M33. Since LPVs are ~5 times more common than Cepheids andhave a well defined PL relation, LPVs provide a promising method forestimating Galactic and extra galactic distances.
| Elemental Abundances in Evolved Supergiants. II. The Young Clusters H and χ Persei
We report on the results of our analyses of high-quality spectra of Msupergiants in the h and χ Persei double cluster. Our temperatureestimates range from 3500 to 4000 K for a sample of 14 stars. There is awide range in the lithium abundances, from [Li/Fe]=-1.7 to[Li/Fe]=-0.10. The 12C/13C ratio ranges from 10 to16 and displays a weak trend with luminosity, such that the moreluminous stars have a slightly smaller ratio. We find a significantexcess of Na, which may be due to its production by proton capture by22Ne. However, there is no evidence for the O deficiency thatusually accompanies a Na excess in globular cluster stars.
| SiO Masers in Stars in the Inner and Outer Galactic Disk
Observations in the J=1--0, v=1 and v=2 ^{{28}} SiO and v=0 ^{{29}} SiOmaser lines were made towards 97 outer- and 19 inner-disk IRAS sourceswith typical IRAS colors of AGB stars. 21 new ^{{28}} SiO and 1 new^{{29}} SiO maser sources were detected above the 5 sigma level of ~ 1Jy with the Nobeyama 45 m telescope. Collecting all of the observationaldata in SiO J=1--0 maser lines taken with a 45 m telescope, a comparisonis made between the outer-disk, inner-disk, and bulge samples. Thesamples, themselves, align a sequence of mid-infrared color, flux at 12mu m and IRAS variability index. The detection rates are 66%, 51%, and31%, respectively, in the bulge, inner disk, and outer disk. This factis consistent with the tendency of increasing proportion of C-rich starsin the IRAS sample and metallicity gradient with the galactocentricdistance.
| Classification and Identification of IRAS Sources with Low-Resolution Spectra
IRAS low-resolution spectra were extracted for 11,224 IRAS sources.These spectra were classified into astrophysical classes, based on thepresence of emission and absorption features and on the shape of thecontinuum. Counterparts of these IRAS sources in existing optical andinfrared catalogs are identified, and their optical spectral types arelisted if they are known. The correlations between thephotospheric/optical and circumstellar/infrared classification arediscussed.
| Red supergiants, neutrinos and the Double Cluster
The Perseus Double Cluster is surrounded by one of the largestconcentrations of red supergiant stars in the sky. As a consequence, thedevelopment of our understanding of the structure and evolution of thesestars has been intimately connected with studies of this cluster. Thispaper traces the history of this connection from the end of the 19thcentury through to the early 1970s.
| An Infrared Color-Magnitude Relationship
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....110.2910H&db_key=AST
| On the duplicity of cool giant and supergiant variable stars
From the analysis of photometric, colorimetric and polarimetric data itfollows that high luminosity red variable stars are divided into twogroups: group I - double stars with brightness variation periods of morethan 480 days, group II - single stars with periods less than 480 days.Moreover, double stars possess: a) high coefficients of correlationbetween brightness V and U - B, B - V colors; b) relatively low valuesof U - B (m5) and high infrared excess; c) strong variations ofparameters of polarization (>1.5) and often those are associated withmaser sources.
| Uir-Band Emission from M Supergiants
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1994MNRAS.266..640S&db_key=AST
| Determination of two groups of high luminosity red variable stars.
Not Available
| Galactic OB associations in the northern Milky Way Galaxy. I - Longitudes 55 deg to 150 deg
The literature on all OB associations was reviewed, and their IRAS pointsource content was studied, between galactic longitude 55 and 150 deg.Only one third of the 24 associations listed by Ruprecht et al. (1981)have been the subject of individual studies designed to identify thebrightest stars. Distances to all of these were recomputed using themethod of cluster fitting of the B main sequence stars, which makes itpoossible to reexamine the absolute magnitude calibration of the Ostars, as well as for the red supergiant candidate stars. Also examinedwas the composite HR diagram for these associations. Associations withthe best defined main sequences, which also tend to contain very youngclusters, referred to here as OB clusters, have extremely few evolved Band A or red supergiants. Associations with poorly defined mainsequences and few OB clusters have many more evolved stars. They alsoshow an effect in the upper HR diagram referred to as a ledge byFitzpatrick and Garmany (1990) in similar data for the Large MagellanicCloud. It is suggested that the differences in the associations are notjust observational selection effects but represent real differences inage and formation history.
| Asymptotic giant branch stars near the sun
Available red and near-infrared photometry and apparent motions of M, S,and C asymptotic giant branch (AGB) stars in the Bright Star Catalogueare tabulated and discussed. It is shown that the red and near infraredindices normally used for late-type stars are interchangeable except forcarbon stars. The M-type giants are variable with visual amplitudegreater than 0.05 mag. The reddening-free parameter m2 from Genevaphotometry is essentially a temperature parameter for M giants, whilethe reddening-free parameter d is a sensitive detector of blue stellarcompanions. The space density of AGB stars near the sun decreases by afactor of 35 in a temperature range 3800 to 3400 K. Two of the S starsnear the sun were found to have nearly equal space motions and may becomembers of the Arcturus group.
| Mass-losing M supergiants in the solar neighborhood
A list of the 21 mass-losing red supergiants (20 M type, one G type; Lgreater than 100,000 solar luminosities) within 2.5 kpc of the sun iscompiled. These supergiants are highly evolved descendants ofmain-sequence stars with initial masses larger than 20 solar masses. Thesurface density is between about 1 and 2/sq kpc. As found previously,these stars are much less concentrated toward the Galactic center thanW-R stars, which are also highly evolved massive stars. Although withconsiderable uncertainty, it is estimated that the mass return by the Msupergiants is somewhere between 0.00001 and 0.00003 solar mass/sq kpcyr. In the hemisphere facing the Galactic center there is much less massloss from M supergiants than from W-R stars, but, in the anticenterdirection, the M supergiants return more mass than do the W-R stars. Theduration of the M supergiant phase appears to be between 200,000 and400,000 yr. During this phase, a star of initially at least 20 solarmasses returns perhaps 3-10 solar masses into the interstellar medium.
| Statistical characteristics of the ten-micron silicate emission in M-type stars
The statistical characteristics of 10 micron silicate emission wereexamined for 1427 M-type stars in the catalog of the Two-Micron SkySurvey using the low-resolution spectra obtained by IRAS. Correlationswere examined of 10 micron silicate emission with the spectralclassification in the visual wavelength region, with near-infrared colorI - K, with a variability type, and with the period of variation. It wasfound that supergiants show silicate emission more frequently than dogiants. Silicate emission was found in stars of all three variabilitytypes: irregular, semiregular, and Mira variables. The proportion ofstars with silicate emission was found to be larger for Mira variables.Most of the Mira variables with periods of variation longer than about450 d were found to show silicate emission.
| Infrared circumstellar shells - Origins, and clues to the evolution of massive stars
The infrared fluxes, spatial and spectral characteristics for a sampleof 111 supergiant stars of spectral types F0 through M5 are tabulated,and correlations examined with respect to the nature of theircircumstellar envelopes. One-fourth of these objects were spatialyresolved by IRAS at 60 microns and possess extended circumstellar shellmaterial, with implied expansion ages of about 10 to the 5th yr.Inferences about the production of dust, mass loss, and the relation ofthese characteristics of the evolution of massive stars, are discussed.
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