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Atmospheric dynamics and the mass loss process in red supergiant stars
Context: Red supergiant stars represent a key phase in the evolution ofmassive stars. Recent radiative hydrodynamic simulations suggest thattheir atmospheres may be the location of large-scale convective motions. Aims: As supergiant convection is expected to generate supersonicmotions and shocks, we seek constraints on these atmospheric motions andtheir possible relation with mass-loss rates. Methods: We presenthigh-resolution, visible spectroscopy of a sample of red supergiants(spectral type M I) and analyse them with a tomographic technique. Results: We observe steep velocity gradients, characterising both upwardand downward supersonic motions, which are time variable on time scalesof a few hundred days. Conclusions: These convective motions willgenerate turbulent pressure, which will strongly decrease the effectivegravity. We suggest that this decrease, combined with radiative pressureon molecular lines, initiate the mass loss in red supergiant stars.
| Proper-motion binaries in the Hipparcos catalogue. Comparison with radial velocity data
Context: .This paper is the last in a series devoted to the analysis ofthe binary content of the Hipparcos Catalogue. Aims: .Thecomparison of the proper motions constructed from positions spanning ashort (Hipparcos) or long time (Tycho-2) makes it possible to uncoverbinaries with periods of the order of or somewhat larger than the shorttime span (in this case, the 3 yr duration of the Hipparcos mission),since the unrecognised orbital motion will then add to the propermotion. Methods: .A list of candidate proper motion binaries isconstructed from a carefully designed χ2 test evaluatingthe statistical significance of the difference between the Tycho-2 andHipparcos proper motions for 103 134 stars in common between the twocatalogues (excluding components of visual systems). Since similar listsof proper-motion binaries have already been constructed, the presentpaper focuses on the evaluation of the detection efficiency ofproper-motion binaries, using different kinds of control data (mostlyradial velocities). The detection rate for entries from the NinthCatalogue of Spectroscopic Binary Orbits (S_B^9) is evaluated, as wellas for stars like barium stars, which are known to be all binaries, andfinally for spectroscopic binaries identified from radial velocity datain the Geneva-Copenhagen survey of F and G dwarfs in the solarneighbourhood. Results: .Proper motion binaries are efficientlydetected for systems with parallaxes in excess of ~20 mas, and periodsin the range 1000-30 000 d. The shortest periods in this range(1000-2000 d, i.e., once to twice the duration of the Hipparcos mission)may appear only as DMSA/G binaries (accelerated proper motion in theHipparcos Double and Multiple System Annex). Proper motion binariesdetected among S_B9 systems having periods shorter than about400 d hint at triple systems, the proper-motion binary involving acomponent with a longer orbital period. A list of 19 candidate triplesystems is provided. Binaries suspected of having low-mass(brown-dwarf-like) companions are listed as well. Among the 37 bariumstars with parallaxes larger than 5 mas, only 7 exhibit no evidence forduplicity whatsoever (be it spectroscopic or astrometric). Finally, thefraction of proper-motion binaries shows no significant variation amongthe various (regular) spectral classes, when due account is taken forthe detection biases.Full Table [see full textsee full text] is only available in electronicform at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/464/377
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| Statistical Constraints for Astrometric Binaries with Nonlinear Motion
Useful constraints on the orbits and mass ratios of astrometric binariesin the Hipparcos catalog are derived from the measured proper motiondifferences of Hipparcos and Tycho-2 (Δμ), accelerations ofproper motions (μ˙), and second derivatives of proper motions(μ̈). It is shown how, in some cases, statistical bounds can beestimated for the masses of the secondary components. Two catalogs ofastrometric binaries are generated, one of binaries with significantproper motion differences and the other of binaries with significantaccelerations of their proper motions. Mathematical relations betweenthe astrometric observables Δμ, μ˙, and μ̈ andthe orbital elements are derived in the appendices. We find a remarkabledifference between the distribution of spectral types of stars withlarge accelerations but small proper motion differences and that ofstars with large proper motion differences but insignificantaccelerations. The spectral type distribution for the former sample ofbinaries is the same as the general distribution of all stars in theHipparcos catalog, whereas the latter sample is clearly dominated bysolar-type stars, with an obvious dearth of blue stars. We point outthat the latter set includes mostly binaries with long periods (longerthan about 6 yr).
| Guilt by Association: The 13 Micron Dust Emission Feature and Its Correlation to Other Gas and Dust Features
A study of all full-scan spectra of optically thin oxygen-richcircumstellar dust shells in the database produced by the ShortWavelength Spectrometer on ISO reveals that the strength of severalinfrared spectral features correlates with the strength of the 13 μmdust feature. These correlated features include dust features at 19.8and 28.1 μm and the bands produced by warm carbon dioxide molecules(the strongest of which are at 13.9, 15.0, and 16.2 μm). The databasedoes not provide any evidence for a correlation of the 13 μm featurewith a dust feature at 32 μm, and it is more likely that a weakemission feature at 16.8 μm arises from carbon dioxide gas ratherthan dust. The correlated dust features at 13, 20, and 28 μm tend tobe stronger with respect to the total dust emission in semiregular andirregular variables associated with the asymptotic giant branch than inMira variables or supergiants. This family of dust features also tendsto be stronger in systems with lower infrared excesses and thus lowermass-loss rates. We hypothesize that the dust features arise fromcrystalline forms of alumina (13 μm) and silicates (20 and 28 μm).Based on observations with the ISO, a European Space Agency (ESA)project with instruments funded by ESA member states (especially thePrincipal Investigator countries: France, Germany, the Netherlands, andthe United Kingdom) and with the participation of the Institute of Spaceand Astronautical Science (ISAS) and the National Aeronautics and SpaceAdministration (NASA).
| 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
| Stars with the Largest Hipparcos Photometric Amplitudes
A list of the 2027 stars that have the largest photometric amplitudes inHipparcos Photometry shows that most variable stars are all Miras. Thepercentage of variable types change as a function of amplitude. Thiscompilation should also be of value to photometrists looking forrelatively unstudied, but large amplitude stars.
| 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
| Silicate and hydrocarbon emission from Galactic M supergiants
Following our discovery of unidentified infrared (UIR) band emission ina number of M supergiants in h and chi Per, we have obtained 10-μmspectra of a sample of 60 galactic M supergiants. Only three newsources, V1749 Cyg, UW Aql and IRC+40 427, appear to show the UIR bands;the others show the expected silicate emission or a featurelesscontinuum. The occurrence of UIR-band emission in M supergiants istherefore much higher in the h and chi Per cluster than in the Galaxy asa whole. Possible explanations for the origin and distribution of UIRbands in oxygen-rich supergiants are discussed. We use our spectra toderive mass-loss rates ranging from 10^-8 to 10^-4 M_solar yr^-1 for thenew sample, based on the power emitted in the silicate feature. Therelationship between mass-loss rate and luminosity for M supergiants isdiscussed, and correlations are explored between their mid-infraredemission properties.
| The Infrared Spectral Classification of Oxygen-rich Dust Shells
This paper presents infrared spectral classifications for a flux-limitedsample of 635 optically identified oxygen-rich variables includingsupergiants and sources on the asymptotic giant branch (AGB). Severalclasses of spectra from oxygen-rich dust exist, and these can bearranged in a smoothly varying sequence of spectral shapes known as thesilicate dust sequence. Classification based on this sequence revealsseveral dependencies of the dust emission on the properties of thecentral star. Nearly all S stars show broad emission features fromalumina dust, while most of the supergiants exhibit classic featuresfrom amorphous silicate dust. Mira variables with symmetric light curvesgenerally show broad alumina emission, while those with more asymmetriclight curves show classic silicate emission. These differences may arisefrom differences in the photospheric C/O ratio.
| 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.
| A Renewed Search for Water Maser Emission from Mira Variables.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114.1602L&db_key=AST
| 1--4 MU M Spectroscopy of Very Red Stars Found in an I-Band Objective Prism Survey
We present the 1.2--4.2 mu m spectroscopy of stars found in an objectiveprism survey of the galactic plane by Stephenson (1992, AAA 55.002.010).These stars were thought by Stephenson to be heavily reddened byinterstellar absorption. However, almost all of them have turned out tobe late-type stars with clear 2.3 mu m CO absorption, which means thatthey are intrinsically red as well. A few stars have AV ~ 9, but mostof them are only moderately reddened (AV = 1--5).
| 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.
| Determination of two groups of high luminosity red variable stars.
Not Available
| Photometry of Vv-Cephei Type 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.
| Photometry of variable AFGL sources
Results of infrared photometric observations of 63 AFGL sources over thepast 9 years are presented. Using these data together with previousmeasurements of these stars, pulsation periods and mean photometriccharacteristics are determined. These stars are found to lie midwaybetween optically identified Mira variables and the radio-luminous OH/IRstars in their period distribution and photometric properties. For thesample as a whole, there is no evidence for sudden or transient behaviorsuch as a switch in pulsation mode. Rather, these stars suggest rapid,but continuous, evolution from shorter period Miras with weak mass lossto longer periods and larger mass-loss rates. The carbon-rich stars inthe sample have the same period distribution as the oxygen-rich stars.None of the carbon stars have periods as long as those of the very longperiod radio-luminous OH/IR stars.
| 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.
| Infrared spectra and circumstellar emission of late-type stars
NIR photometry has been carried out for 63 M-type stars in eightphotometric bands. Four bands were the usual J, H, K, and L bands ofbroad-band photometry, and the other four were defined with relativelynarrow filters at 3.1, 3.3, 3.4, and 3.7 microns to measure the strengthof a stellar H2O absortion band centered at about 2.7 microns. Theeffects of circumstellar emission due to silicate dust on the energyspectra of oxygen-rich stars are extracted on the basis of the presentdata and IRAS photometric data. Peculiar carbon stars which exhibit asilicatelike emission feature at 10 microns were searched for from about1800 carbon stars. Eleven new candidate carbon stars were found.
| Circumstellar environments. III - M-supergiants
Spectra of M-supergiants in the 7-100-micron region are studied. Thecircumstellar silicate dust features at 9.7 and 18 microns are found tobe of variable width. Although most stars are shown to exhibit theclassical circumstellar silicate dust features typified by those ofAlpha Ori, some, such as VX SGr, exhibit much broader features.Mass-loss rates are given for 31 M-supergiants.
| Hot components and circumstellar grains in M supergiant syncretic binaries
Ultraviolet and infrared spectra were obtained in order to study grainsin cool star and hot star syncretic type binaries. Grains are found inonly about half of the syncretic systems. The results suggest thatgrains have not formed in many syncretic systems because of ultravioletradiation from the hot star. Circumstellar extinction could not beunambiguously detected in those systems with grains.
| The cool components of symbiotic stars. I - Optical spectral types
An analysis of prominent absorption features on red spectra of symbioticstars is presented. The depths of TiO and VO bands appear to becorrelated with the brightness of the system; this behavior is probablythe result of the secondary star heating the outer atmosphere of thecool giant. New spectral types and luminosity classes for the coolcomponents of symbiotics are derived, and these classifications suggesta division into semidetached systems and detached systems. Mass-lossrates for detached symbiotics, which do not contain Mira variables,remain higher than those estimated for single red giants of the samespectral type, suggesting that the presence of a binary companionenhances mass loss in these objects.
| Models for IRAS observations of circumstellar dust shells around late-type stars
IRAS observations of circumstellar dust shells around late-type starsare compared with the models of Rowan-Robinson and Harris (1982, 1983).It is shown that the IRAS data at 12 and 25 microns agree well withprevious observations and models. The predicted fluxes at 60 microns andabove are found to depend sensitively on the overall extent of the dustshells. Models for circumstellar dust shells around carbon and M starsare compared with IRAS observations at 60 and 100 microns and are foundto agree reasonably well with model predictions. For M stars, the IRASdata at 60 and 100 microns require a grain absorption efficiency between25-30 and 100 microns.
| IRAS catalogues and atlases - Atlas of low-resolution spectra
Plots of all 5425 spectra in the IRAS catalogue of low-resolutionspectra are presented. The catalogue contains the average spectra ofmost IRAS poiont sources with 12 micron flux densities above 10 Jy.
| Determination of the interstellar component in the linear polarization of the light of red supergiants
Not Available
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| קבוצת-כוכבים: | לטאה |
| התרוממות ימנית: | 22h47m43.43s |
| סירוב: | +55°09'30.3" |
| גודל גלוי: | 8.54 |
| מרחק: | 3846.154 פארסק |
| תנועה נכונה: | -2.7 |
| תנועה נכונה: | -4.7 |
| B-T magnitude: | 11.412 |
| V-T magnitude: | 8.778 |
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