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Infrared photometry and evolution of mass-losing AGB stars. I. Carbon stars revisited
As part of a reanalysis of galactic Asymptotic Giant Branch (AGB) starsat infrared (IR) wavelengths, we discuss a sample (357) of carbon starsfor which mass loss rates, near-IR photometry and distance estimatesexist. For 252 sources we collected mid-IR fluxes from the MSX (6C) andthe ISO-SWS catalogues. Most stars have spectral energy distributions upto 21 μm, and some (1/3) up to 45 μm. This wide wavelengthcoverage allows us to obtain reliable bolometric magnitudes. Theproperties of our sample are discussed with emphasis on ~70 stars withastrometric distances. We show that mid-IR fluxes are crucial toestimate the magnitude of stars with dusty envelopes. We construct HRdiagrams and show that the luminosities agree fairly well with modelpredictions based on the Schwarzschild's criterion, contrary to what iswidely argued in the literature. A problem with the brightness of Cstars does not appear to exist. From the relative number of Mira andSemiregular C-variables, we argue that the switch between these classesis unlikely to be connected to thermal pulses. The relevance of the twopopulations varies with the evolution, with Miras dominating the finalstages. We also analyze mass loss rates, which increase for increasingluminosity, but with a spread that probably results from a dependence ona number of parameters (like e.g. different stellar masses and differentmechanisms powering stellar winds). Instead, mass loss rates are wellmonitored by IR colours, especially if extended to 20 μm and beyond,where AGB envelopes behave like black bodies. From these colours theevolutionary status of various classes of C stars is discussed.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| The mass loss of C-rich giants
The mass loss rates, expansion velocities and dust-to-gas density ratiosfrom millimetric observations of 119 carbon-rich giants are compared, asfunctions of stellar parameters, to the predictions of recenthydrodynamical models. Distances and luminosities previously estimatedfrom HIPPARCOS data, masses from pulsations and C/O abundance ratiosfrom spectroscopy, and effective temperatures from a new homogeneousscale, are used. Predicted and observed mass loss rates agree fairlywell, as functions of effective temperature. The signature of the massrange M≤4 Mȯ of most carbon-rich AGB stars is seenas a flat portion in the diagram of mass loss rate vs. effectivetemperature. It is flanked by two regions of mass loss rates increasingwith decreasing effective temperature at nearly constant stellar mass.Four stars with detached shells, i.e. episodic strong mass loss, andfive cool infrared carbon-rich stars with optically-thick dust shells,have mass loss rates much larger than predicted values. The latter(including CW Leo) could be stars of smaller masses (M≃ 1.5-2.5Mȯ) while M≃ 4 Mȯ is indicated formost of the coolest objects. Among the carbon stars with detachedshells, R Scl returned to a predicted level (16 times lower) accordingto recent measurements of the central source. The observed expansionvelocities are in agreement with the predicted velocities at infinity ina diagram of velocities vs. effective temperature, provided the carbonto oxygen abundance ratio is 1≤ɛ C/ɛO≤2, i.e. the range deduced from spectra and modelatmospheres of those cool variables. Five stars with detached shellsdisplay expansion velocities about twice that predicted at theireffective temperature. Miras and non-Miras do populate the same locus inboth diagrams at the present accuracy. The predicted dust-to-gas densityratios are however about 2.2 times smaller than the values estimatedfrom observations. Recent drift models can contribute to minimize thediscrepancy since they include more dust. Simple approximate formulaeare proposed.This research has made use of the Simbad database operated at CDS.Partially based on data from the ESA HIPPARCOS astrometry satellite.Table 3 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/429/235
| 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
| Carbon-rich giants in the HR diagram and their luminosity function
The luminosity function (LF) of nearly 300 Galactic carbon giants isderived. Adding BaII giants and various related objects, about 370objects are located in the RGB and AGB portions of the theoretical HRdiagram. As intermediate steps, (1) bolometric corrections arecalibrated against selected intrinsic color indices; (2) the diagram ofphotometric coefficients 1/2 vs. astrometric trueparallaxes varpi are interpreted in terms of ranges of photosphericradii for every photometric group; (3) coefficients CR andCL for bias-free evaluation of mean photospheric radii andmean luminosities are computed. The LF of Galactic carbon giantsexhibits two maxima corresponding to the HC-stars of the thick disk andto the CV-stars of the old thin disk respectively. It is discussed andcompared to those of carbon stars in the Magellanic Clouds and Galacticbulge. The HC-part is similar to the LF of the Galactic bulge,reinforcing the idea that the Bulge and the thick disk are part of thesame dynamical component. The CV-part looks similar to the LF of theLarge Magellanic Cloud (LMC), but the former is wider due to thesubstantial errors on HIPPARCOS parallaxes. The obtained meanluminosities increase with increasing radii and decreasing effectivetemperatures, along the HC-CV sequence of photometric groups, except forHC0, the earliest one. This trend illustrates the RGB- and AGB-tracks oflow- and intermediate-mass stars for a range in metallicities. From acomparison with theoretical tracks in the HR diagram, the initial massesMi range from about 0.8 to 4.0 Msun for carbongiants, with possibly larger masses for a few extreme objects. A largerange of metallicities is likely, from metal-poor HC-stars classified asCH stars on the grounds of their spectra (a spheroidal component), tonear-solar compositions of many CV-stars. Technetium-rich carbon giantsare brighter than the lower limit Mbol =~ -3.6+/- 0.4 andcentered at =~-4.7+0.6-0.9 at about =~(2935+/-200) K or CV3-CV4 in our classification. Much like the resultsof Van Eck et al. (\cite{vaneck98}) for S stars, this confirms theTDU-model of those TP-AGB stars. This is not the case of the HC-stars inthe thick disk, with >~ 3400 K and>~ -3.4. The faint HC1 and HC2-stars( =~ -1.1+0.7-1.0) arefound slightly brighter than the BaII giants ( =~-0.3+/-1.3) on average. Most RCB variables and HdC stars range fromMbol =~ -1 to -4 against -0.2 to -2.4 for those of the threepopulation II Cepheids in the sample. The former stars show the largestluminosities ( <~ -4 at the highest effectivetemperatures (6500-7500 K), close to the Mbol =~ -5 value forthe hot LMC RCB-stars (W Men and HV 5637). A full discussion of theresults is postponed to a companion paper on pulsation modes andpulsation masses of carbon-rich long period variables (LPVs; Paper IV,present issue). This research has made use of the Simbad databaseoperated at CDS, Strasbourg, France. Partially based on data from theESA HIPPARCOS astrometry satellite. Table 2 is only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/390/967
| 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.
| 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).
| The effective temperatures of carbon-rich stars
We evaluate effective temperatures of 390 carbon-rich stars. Theinterstellar extinction on their lines of sights was determined andcircumstellar contributions derived. The intrinsic (dereddened) spectralenergy distributions (SEDs) are classified into 14 photometric groups(HCi, CVj and SCV with i=0,5 and j=1,7). The newscale of effective temperatures proposed here is calibrated on the 54angular diameters (measured on 52 stars) available at present from lunaroccultations and interferometry. The brightness distribution on stellardiscs and its influence on diameter evaluations are discussed. Theeffective temperatures directly deduced from those diameters correlatewith the classification into photometric groups, despite the large errorbars on diameters. The main parameter of our photometric classificationis thus effective temperature. Our photometric < k right >1/2 coefficients are shown to be angular diameters on arelative scale for a given photometric group, (more precisely for agiven effective temperature). The angular diameters are consistent withthe photometric data previously shown to be consistent with the trueparallaxes from HIPPARCOS observations (Knapik, et al. \cite{knapik98},Sect. 6). Provisional effective temperatures, as constrained by asuccessful comparison of dereddened SEDs from observations to modelatmosphere predictions, are in good agreement with the values directlycalculated from the observed angular diameters and with those deducedfrom five selected intrinsic color indices. These three approaches wereused to calibrate a reference angular diameter Phi 0 and theassociated coefficient CT_eff. The effective temperatureproposed for each star is the arithmetic mean of two estimates, one(``bolometric'') from a reference integrated flux F0, theother (``spectral'') from calibrated color indices which arerepresentative of SED shapes. Effective temperatures for about 390carbon stars are provided on this new homogeneous scale, together withvalues for some stars classified with oxygen-type SEDs with a total of438 SEDs (410 stars) studied. Apparent bolometric magnitudes are given.Objects with strong infrared excesses and optically thick circumstellardust shells are discussed separately. The new effective temperaturescale is shown to be compatible and (statistically) consistent with thesample of direct values from the observed angular diameters. Theeffective temperatures are confirmed to be higher than the mean colortemperatures (from 140 to 440 K). They are in good agreement with thepublished estimates from the infrared flux method forTeff>= 3170 K, while an increasing discrepancy is observedtoward lower temperatures. As an illustration of the efficiency of thephotometric classification and effective temperature scale, the C/Oratios and the Merrill-Sanford (M-S) band intensities are investigated.It is shown that the maximum value, mean value and dispersion of C/Oincrease along the photometric CV-sequence, i.e. with decreasingeffective temperature. The M-S bands of SiC2 are shown tohave a transition from ``none'' to ``strong'' at Teff =~(2800+/- 150right ) K. Simultaneously, with decreasing effectivetemperature, the mean C/O ratio increases from 1.04 to 1.36, thetransition in SiC2 strength occurring while 1.07<= C/O<= 1.18. This research has made use of the Simbad database operatedat CDS, Strasbourg, France. Table 10 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/369/178
| General Catalog of Galactic Carbon Stars by C. B. Stephenson. Third Edition
The catalog is an updated and revised version of Stephenson's Catalogueof Galactic Cool Carbon Stars (2nd edition). It includes 6891 entries.For each star the following information is given: equatorial (2000.0)and galactic coordinates, blue, visual and infrared magnitudes, spectralclassification, references, designations in the most significantcatalogs and coordinate precision classes. The main catalog issupplemented by remarks containing information for which there was noplace in entries of the main part, as well as some occasional notesabout the peculiarities of specific stars.
| Coordinates and Identifications for Sonneberg Variables on MVS 308-316
Not Available
| 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.
| Quantitative analysis of carbon isotopic ratios in carbon stars. I. 62 N-type and 15 SC-type carbon stars.
We present a result of quantitative analysis of ^12^C/^13^C ratios in 62N-type and 15 SC-type carbon stars. By the use of CCD as a detector wecan obtain spectra of resolution ~20,000 with enough signal-to-noiseratios for a large number of carbon stars, for which ^12^C/^13^C ratioshave not yet been derived. Carbon isotopic ratios are determined fromlines of the CN red system around 8000A, based on the iso-intensitymethod and line-blanketed model atmospheres. The average of ^12^C/^13^Cratios in 62 N-type carbon stars is found to be 27+/-11 (standarddeviation). The majority of the N-type carbon stars studied (about 85%)are found to have ^12^C/^13^C ratios less than 40, and the number ofstars which have ^12^C/^13^C ratios larger than 40 is found to berelatively small. This result shows a marked contrast to some of theprevious results that have shown the opposite distribution, namely,^12^C/^13^C ratios mostly larger than 40 in N-type carbon stars. Theaverage of ^12^C/^13^C ratios in 15 SC-type carbon stars is found to be22+/-14 (standard deviation). Most of the SC-type carbon stars studiedare found to have ^12^C/^13^C ratios larger than 10, while only three ofthem turn out to be ^13^C-rich. This is in contrast with the earlierclassification based on low resolution spectra which classified them asJ-type, that is, ^13^C-rich. The earlier temperature scale whichclassified SC-type carbon stars as the latest (C8-9) based on theirstrong NaI D lines can not be necessarily justified. The strong NaI Dlines of SC stars should be attributed to the peculiar atmosphericstructure due to C/O ratios very near to unity. The resulting^12^C/^13^C ratios are partly consistent with the scenario in which Mgiants evolve through SC-type to N-type carbon stars, as ^12^C producedduring the helium shell flash is added to the envelope.
| Spectral indexes of cool carbon stars in the near-infrared region. III.
Not Available
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| A Catalog of li Abundances and Equivalent Widths in a Sample of Galactic C-Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&AS..102..361B&db_key=AST
| Evolution from visual to infrared carbon stars: Interrupted mass-loss model
a set of self-consistent model calulations of the evolution from visualcarbon stars to infrared carbon stars is presented. A two-shell systemmodel, the interrurpted mass-loss model (oxygen-rich detached shell andnewly forming SiC dust shell), has been developed. This model overcomesthe shortcomings of the single detached-shell model (Chan and Kwok 1988)and the SiC shell model (Chan and Kwok 1990). A new mass-loss formula,which describes the gradually increasing mass-loss rate at the earlystage of the infrared carbon stars, is introduced to simulate the effectof the newly forming SiC shell. The model tracks successfully explain a'C' -shaped distribution of carbon stars in the color-color diagram. Theenergy distributions of approximately 110 transition objects are fittedwith devloping SiC dust shells using the interrupted mass-loss model.The existence of these transition objects with infrared propertiesintermediate between visual and infrared carbon stars, lends futhersupport to the idea of an evolutionary link between visual and infraredcabon stars.
| The radio properties of high-redshift quasars. I - Dual-frequency observations of 79 steep-spectrum quasars at Z over 1.5
We have made sensitive VLA observations of virtually all knownhigh-redshift radio-loud QSOs with extended radio morphologies. Theresulting images have angular resolutions of typically 0.4 and 0.15arcsec and are compiled here. This compilation of maps will permit theextraction of numerous radio source parameters, constituting a data basefor comprehensive statistical analyses to be explored in subsequentpapers. The data base is particularly useful for statistical studies.The key characteristics of the sample are the narrow redshift range, thenarrow distribution in linear resolutions of the maps, the narrowdistribution of map sensitivity to emitting regions of standard physicalcharacteristics, and the relatively narrow range of source luminosities.As a result of these properties, the sample enjoys relative freedom fromthe effects of parameter correlations with redshift and luminosity. Abrief discussion of the sample characteristics and some elaboration ofthe particular advantages of this sample are presented. Some cleartrends in the data are discussed briefly.
| Circumstellar shells resolved in the IRAS survey data. I - Data processing procedure, results, and confidence tests
We have examined the IRAS 60 and 100 micron survey data covering 512evolved stars and young planetary nebulae for evidence of spatiallyresolved structure. A simple model, consisting of a central unresolvedsource surrounded by a resolved isothermal shell, was fitted to the datafor each star. Seventy-six stars were found to be resolved in the 60micron data. Tests have been performed to verify that the extendedstructure seen is not an artifact of the data-processing algorithm.
| Photoelectric photometry of carbon stars in the Vilnius system
A total of 368 observations of magnitudes and color indices of 178carbon stars in the Vilnius seven-color photometric system are given.The observations are presented in a catalog.
| Photoelectric photometry of carbon, barium and related stars in the Vilnius system and their colour excesses. II
The paper contains a catalogue of 63 galactic field carbon, barium, andrelated stars. The catalogue presents the results of photoelectricphotometry in the Vilnius system, together with the data compiled fromthe literature. Several methods are used to estimate color excessesE(B-V) of the stars.
| Spectral indexes of cool carbon stars in the near-infrared region. II
Following the previous paper (Tanaka et al., 1990, hereafter as PaperI), near-infrared spectroscopic observations of cool carbon stars havebeen continued with the Fourier transform spectrometer and the 188 cmreflector at Okayama Astrophysical Observatory. Sixty-six spectra of 63carbon stars were analyzed. Eighteen stars were newly added to theprogram stars, and the total number of the analyzed carbon stars reached101. Three spectral indexes defined in Paper I; the color index, theCO-index, and the C2-index were measured. The same analysis was madeindependently as before, because the spectra were taken at differentphases of their variabilities and their signal-to-noise ratios were muchimproved by careful observations. General trends of the results obtainedin Paper I are confirmed.
| The mass range of carbon stars
This paper considers the existence of a population of carbon stars thatis more massive than that described by Claussen et al. (1987) (1.2-1.6solar mass). These more massive stars are characterized by molecularenvelopes that expand at velocities V-infinity not less than 17.5 km/sand confinemenet to low Galactic latitude. An exponential fit to heightabove the Galactic plane demonstrates that the carbon stars with highV-infinity are described by a smaller scale height, 107 pc, than thatwhich characterizes carbon stars with low V-infinity, 270 pc. A 100-pcscale height is characteristic of main-sequence stars of mass not lessthan 2.5-4 solar masses. The larger ratio of 12 to 2 micron fluxes forhigh V-infinity carbon stars as compared with other carbon starsdemonstrates that the former group is more dust obscured. Based on theincidence of optical designations, H-alpha emission, and the12-micron/2-micron ratio, the stars with larger V-infinity generallyhave larger mass-loss rates and might dominate the mass returned bycarbon stars to the ISM.
| Mass loss from red giant stars. II - Carbon stars
A millimeter-wave survey has been made of bright relatively unobscured,carbon stars, chosen on the basis of their optical properties. Out of 26program objects, (J = 2-1)CO emission is detected from 15. Most of thesehad not been previously detected. There are many differences among theobserved objects, but one rather interesting trend emerges: a positivecorrelation, at moderate IR excesses, between the IR dust emission andthe expansion velocity of the dense wind. A similar, positivecorrelation with the mass-loss rate implies that stars with larger massfluxes also accelerate them to larger velocities. At high-IR excesses,both correlations break down, and the momentum rate may be limited bythe momentum rate of the stellar radiation. All these effects could beascribed to differences in the gas-to-dust ratio, assuming thatradiation pressure initiates and accelerates the wind.
| Outflow velocities from carbon stars
A plot of outflow velocity versus galactic latitude for a sample of 103galactic stars suggests that carbon stars must originate from stars thathad a fairly wide range of masses when they were on the main sequence.The CO rotational emission J = 2 to 1 or 1 to 0 has been detected in thecircumstellar envelopes around 22 red giant stars and one planetarynebula. The molecular gas toward NGC 6302 is shown to be associated withthe planetary nebula.
| A general catalogue of cool carbon stars
Not Available
| The Analyses of Molecular Spectrum of N-Type Stars with the Model Atmospheres
Not Available
| IRAS low-resolution spectra of cool carbon stars. II - Stars with thin circumstellar shells. III - Stars with thick circumstellar shells
IRAS low-resolution spectra and broad-band data and near-IR photometryare analyzed for 72 carbon stars with near-IR color temperatures over2000 K. Seven stars have an almost featureless spectrum without dustemission in the LRS wavelength region. The majority of the sample starshave the 11.5 micron SiC and an unidentified 8.6 micron emission featuresuperposed on the stellar continuum. The strength of the latter featurecorrelates with the strength of the 3 micron absorption band and isprobably of molecular origin. The broad-band data exhibit a 60 micronexcess which is ascribed to a cool dust shell. The IR spectral energydistributions of those stars with thick circumstellar shells areanalyzed. The slope of the far-IR flux can best be explained by theexistence of a well-defined outer boundary of the dust shell. Thetemperature at this outer boundary implies that the present high massloss rate started 100-1000 yr ago.
| On the violet flux of N type carbon stars
New six-color violet photometry of 26 carbon stars is presented. Theseobservations reveal the shape of the spectrum between 3400 and 4500 Aand provide a measurement of the violet flux deficiency. The strength ofthe 11.5-micron SiC emission feature was also measured usingground-based infrared spectrophotometry and the IRAS low-resolutionspectral catalog. The lack of correlation between the 11.5-micronemission and the violet flux deficiency leads to the conclusion that SiCis not the predominant violet opacity source in N type carbon stars. Theviolet photometry presented here does not quantitatively agree withprevious spectrophotometry that supported C3 as the opacity source. Theobservations alone do not rule out the C3 opacity, but when they arecombined with IUE data, the C3 opacity appears less plausible.
| Speckle-interferometric search for multiple carbon stars.
Not Available
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