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UIR bands in the ISO SWS spectrum of the carbon star TU Tauri
Polycyclic Aromatic Hydrocarbon (PAH) molecules are thought to form inthe ejecta of carbon-rich Asymptotic Giant Branch (AGB) stars. Fifty ISOSWS spectra of warm carbon-rich AGB stars have been investigated for theUnidentified IR (UIR) emission due to fluorescence by PAH molecules. Inthis sample the binary star TU Tau, which has a blue companion, showsinteresting spectral structure in the appropriate wavelength regions.The profiles of the UIR bands in TU Tau have been derived by comparingto suitable carbon-star spectra. The presence of the UIR bands in TU Tauis attributed to UV photons originating from the A2 companion star whichare necessary to excite PAH molecules. The absence of the UIR bands inthe remainder of the sample is ascribed to the lack of UV (or visible)photons in their environment. Hence, the absence of UIR bands does notnecessarily imply the absence of circumstellar PAHs in these sources.The derived UIR band profiles have been compared to UIR band profilesfrom Reflection Nebulae, Planetary Nebulae (PNe), Hii regions, YoungStellar Objects, evolved stars and Galaxies. The profiles of TU Tau areshown to have the most resemblance to those from PNe. Integrated bandflux ratios have also been determined and compared to object type fluxratio correlations found in other studies. Here no definite match wasfound. TU Tau is the only binary with a blue companion in this sample ofAGB stars. In line with earlier studies, we suggest that the bluephotons provided by this companion are required for efficient excitationof PAH molecules in AGB ejecta. In addition, we argue that these bluephotons may promote complex chemistry in the ejecta of TU Tau. Thesimilarity in the peak profiles observed in the spectrum of TU Tau withthose in the spectra of PNe indicates that PAHs are formed in thecircumstellar envelope of carbon-rich AGB stars and make it largelyunmodified into the PNe phase. The variations in the band strengthratios between the different objects has been linked to the ionizationstate of PAHs and reflects the different physical environments betweenthis AGB star and PNe. In contrast, the variation in UIR band profilesbetween stellar ejecta and the Interstellar Medium (ISM) are largelyattributed to chemical modifications during the ISM phase.
| 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.
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| Three-micron spectra of AGB stars and supergiants in nearby galaxies
The dependence of stellar molecular bands on the metallicity is studiedusing infrared L-band spectra of AGB stars (both carbon-rich andoxygen-rich) and M-type supergiants in the Large and Small MagellanicClouds (LMC and SMC) and in the Sagittarius Dwarf Spheroidal Galaxy. Thespectra cover SiO bands for oxygen-rich stars, and acetylene (C2H2), CHand HCN bands for carbon-rich AGB stars. The equivalent width ofacetylene is found to be high even at low metallicity. The high C2H2abundance can be explained with a high carbon-to-oxygen (C/O) ratio forlower metallicity carbon stars. In contrast, the HCN equivalent width islow: fewer than half of the extra-galactic carbon stars show the 3.5μm HCN band, and only a few LMC stars show high HCN equivalent width.HCN abundances are limited by both nitrogen and carbon elementalabundances. The amount of synthesized nitrogen depends on the initialmass, and stars with high luminosity (i.e. high initial mass) could havea high HCN abundance. CH bands are found in both the extra-galactic andGalactic carbon stars. One SMC post-AGB star, SMC-S2, shows the 3.3μm PAH band. This first detection of a PAH band from an SMC post-AGBstar confirms PAHs can form in these low-metallicity stars. None of theoxygen-rich LMC stars show SiO bands, except one possible detection in alow quality spectrum. The limits on the equivalent widths of the SiObands are below the expectation of up to 30 Å for LMC metallicity.Several possible explanations are discussed, mostly based on the effectof pulsation and circumstellar dust. The observations imply that LMC andSMC carbon stars could reach mass-loss rates as high as their Galacticcounterparts, because there are more carbon atoms available and morecarbonaceous dust can be formed. On the other hand, the lack of SiOsuggests less dust and lower mass-loss rates in low-metallicityoxygen-rich stars. The effect on the ISM dust enrichment is discussed.
| CHARM2: An updated Catalog of High Angular Resolution Measurements
We present an update of the Catalog of High Angular ResolutionMeasurements (CHARM, Richichi & Percheron \cite{CHARM}, A&A,386, 492), which includes results available until July 2004. CHARM2 is acompilation of direct measurements by high angular resolution methods,as well as indirect estimates of stellar diameters. Its main goal is toprovide a reference list of sources which can be used for calibrationand verification observations with long-baseline optical and near-IRinterferometers. Single and binary stars are included, as are complexobjects from circumstellar shells to extragalactic sources. The presentupdate provides an increase of almost a factor of two over the previousedition. Additionally, it includes several corrections and improvements,as well as a cross-check with the valuable public release observationsof the ESO Very Large Telescope Interferometer (VLTI). A total of 8231entries for 3238 unique sources are now present in CHARM2. Thisrepresents an increase of a factor of 3.4 and 2.0, respectively, overthe contents of the previous version of CHARM.The catalog is 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/431/773
| 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
| Heavy element abundances in AGB stars . The Hyades giants
This research summarises our methodology for obtaining equivalent widthsand abundances in giant stars. As an initial study, two of the fourgiants from the Hyades cluster have been analysed for heavy elementabundances, specifically s-process elements. This paper displays theresults obtained for HD28305 and HD27371, with most heavy elementabundances proving to be the same in both stars and similar to thoseobtained in previous studies. The extension of these techniques to M, Sand C stars is also discussed.
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| Carbon Stars in the Uves Paranal Observatory Project
The high resolution spectra of five cool carbon stars (X TrA, TW Hor, WOri, U Ant and U Hya) obtained in the UVES Paranal Observatory Projectwere used to examine the quality of R. A. Bell's line-list forsynthesizing the spectra of cool carbon stars. We propose theimprovements of this line-list and estimate the abundances of severalchemical elements.
| The Indo-US Library of Coudé Feed Stellar Spectra
We have obtained spectra for 1273 stars using the 0.9 m coudéfeed telescope at Kitt Peak National Observatory. This telescope feedsthe coudé spectrograph of the 2.1 m telescope. The spectra havebeen obtained with the no. 5 camera of the coudé spectrograph anda Loral 3K×1K CCD. Two gratings have been used to provide spectralcoverage from 3460 to 9464 Å, at a resolution of ~1 Å FWHMand at an original dispersion of 0.44 Å pixel-1. For885 stars we have complete spectra over the entire 3460 to 9464 Åwavelength region (neglecting small gaps of less than 50 Å), andpartial spectral coverage for the remaining stars. The 1273 stars havebeen selected to provide broad coverage of the atmospheric parametersTeff, logg, and [Fe/H], as well as spectral type. The goal ofthe project is to provide a comprehensive library of stellar spectra foruse in the automated classification of stellar and galaxy spectra and ingalaxy population synthesis. In this paper we discuss thecharacteristics of the spectral library, viz., details of theobservations, data reduction procedures, and selection of stars. We alsopresent a few illustrations of the quality and information available inthe spectra. The first version of the complete spectral library is nowpublicly available from the National Optical Astronomy Observatory(NOAO) via ftp and http.
| Molecular and dust features of 29 SiC carbon AGB stars
We have reduced and analyzed the Infrared Space Observatory (ISO)Short-Wavelength Spectrometer (SWS) spectra of 29 infrared carbon starswith a silicon carbide feature at 11.30 μm, 17 of which have not beenpreviously published. Absorption or emission features of C2,HCN, C2H2, C3 and silicon carbide (SiC)have been identified in all 17 unpublished carbon stars. In addition,two unidentified absorption features at 3.50 and 3.65 μm are listedfor the first time in this paper. We classify these 29 carbon stars intogroups A, B, C and D according to the shapes of their spectral energydistribution, and this classification seems to show an evolutionarysequence of carbon stars with an SiC feature. Moreover we have found thefollowing results for the different groups: on average, the relativeintegrated flux of the 3.05 μm C2H2+HCNabsorption feature increases gradually from group A to B and C; that ofthe 5.20 μm C3 absorption feature becomes gradually weakerfrom group A to B and C; that of the 11.30 μm SiC emission featureincreases gradually from group A to B and C but weakens in group D; andin contrast, that of the 13.70 μm C2H2absorption feature weakens gradually from group A to B and C but becomesstronger in group D. We suggest that the evolution of the IR spectra ofcarbon stars along the sequence A to D is a result of the followingphenomena: as the near-IR black-body temperature (Tnir)decreases, the circumstellar envelope becomes thicker; also theeffective temperature (Teff) of the photosphere of thecentral star decreases gradually and the C/O ratio increases from A toB.Based on observations with ISO, an ESA project with instruments fundedby ESA Member States (especially the PI countries: France, Germany, TheNetherlands and the UK) with the participation of ISAS and NASA.
| MgS in detached shells around carbon stars. Mining the mass-loss history
We investigate the dust composition of detached shells around carbonstars, with a focus to understand the origin of the coolmagnesium-sulfide (MgS) material around warm carbon stars, which hasbeen detected around several of these objects\citep{2002A&A...390..533H}. We build a radiative transfer model ofa carbon star surrounded by an expanding detached shell of dust. Theshell contains amorphous carbon grains and MgS grains. We find that asmall fraction of MgS dust (2% of the dust mass) can give a significantcontribution to the IRAS 25 μm flux. However, the presence of MgS inthe detached shell cannot be inferred from the IRAS broadband photometryalone but requires infrared spectroscopy.We apply the model to the detached-shell sources R Scl and U Cam, bothexhibiting a cool MgS feature in their ISO/SWS spectra. We use the shellparameters derived for the molecular shell, using the CO submillimetremaps \citep{1999A&A...351L...1L,2001A&A...368..969S}. Themodels, with MgS grains located in the detached shell, explain the MgSgrain temperature, as derived from their ISO spectra, very well. Thisdemonstrates that the MgS grains are located at the distance of thedetached shell, which is a direct indication that these shells originatefrom a time when the stellar photosphere was already carbon-rich. In thecase of R Scl, the IRAS photometry is simultaneously explained by thesingle shell model. In the case of U Cam, the IRAS photometry is underpredicted, pointing to a contribution from cooler dust located evenfarther away from the star than the molecular shell.We present a simple diagnostic to constrain the distance of the shellusing the profile of the MgS emission feature. The emission featureshifts to longer wavelength with decreasing grain temperature. One cantherefore infer a temperature and a corresponding distance to the starfrom the observed profile. Such a diagnostic might prove useful forfuture studies of such systems with SIRTF or SOFIA.based on observations obtained with ISO, an ESA project with instrumentsfunded by ESA member states (especially the PI countries: France,Germany, the Netherlands and UK) with the participation of ISAS andNASA.}
| Infrared investigation from earth and space on the evolutionary state of a sample of LPV
We selected a sample of highly reddened AGB stars among the sourcesobserved with the SWS instrument on the ISO satellite. These SWS dataallow us to compute the source's photometry in the mid-IR filters of thecamera TIRCAM at the TIRGO telescope. Our photometric data, supplementedwith other measurements taken from the literature, permit to select thecarbon-rich sources in the sample. For these stars, a linear relationholds between dust mass loss and the color index [8.8]-[12.5]. One maythen, from photometric data alone, evaluate the total mass loss (forwhich we used the estimate of \citet{loup}, based on radio data). Theoxygen-rich sources, on the other hand, are distributed in two branches,of which the upper one appears superimposed with carbon stars; the starsin this group have both high luminosity and high wind velocity andtherefore higher masses. Finally S stars lie between the carbon-starbranch and the low-mass oxygen-rich stars, in agreement with theirintermediate evolutionary status.
| On the Origin of Long Secondary Periods in Semiregular Variables
The presence of a long secondary period (LSP) in the light curves ofsome local semiregular variables has been known for many years.Furthermore, the LSPs have recently been found in the light curves ofapproximately 25% of the semiregular variables in the LMC. Theytypically have a length of ~500-4000 days, some 5-15 times longer thanthe primary period. Binarity, pulsation, periodic dust ejection, androtation have been suggested as the origin of the LSPs. Here we analyzeechelle spectra of a group of local semiregular variables with LSPs(hereafter LSPVs) in order to try to distinguish between thesesuggestions. In general, we find that LSPVs do not have broader spectralfeatures than semiregulars without a long secondary period (hereafternon-LSPVs). The general upper limit on the equatorial rotation velocityof 3 km s-1 rules out rotating spot and similar models. OneLSPV, V Hya, does have broader spectral lines than similar carbon stars,but it is shown here that rotation alone is not a good model forexplaining the broad lines. Mid-infrared colors of LSPs and non-LSPVsare similar and there are no LSPVs showing the large (60-25) μm IRAScolor exhibited by some R Coronae Borealis (RCB) stars. Thus, there isno evidence for periodic dust ejection from LSPVs. Finally, we find thatthe LSPVs show larger radial velocity variations than non-LSPVs, whichsuggests that LSPs are caused either by binarity or by pulsation. Asimilar conclusion was derived by Hinkle and co-workers.
| Infrared Colors and Variability of Evolved Stars from COBE DIRBE Data
For a complete 12 μm flux-limited sample of 207 IRAS sources(F12>=150 Jy, |b|>=5deg), the majority ofwhich are AGB stars (~87%), we have extracted light curves in seveninfrared bands between 1.25 and 60 μm using the database of theDiffuse Infrared Background Experiment (DIRBE) instrument on the CosmicBackground Explorer (COBE) satellite. Using previous infrared surveys,we filtered these light curves to remove data points affected by nearbycompanions and obtained time-averaged flux densities and infraredcolors, as well as estimates of their variability at each wavelength. Inthe time-averaged DIRBE color-color plots, we find clear segregation ofsemiregulars, Mira variables, carbon stars, OH/IR stars, and red giantswithout circumstellar dust (i.e., V-[12]<5) and with little or novisual variation (ΔV<0.1 mag). The DIRBE 1.25-25 μm colorsbecome progressively redder and the variability in the DIRBE databaseincreases along the oxygen-rich sequence nondusty slightly varying redgiants-->SRb/Lb-->SRa-->Mira-->OH/IR and the carbon-richSRb/Lb-->Mira sequence. This supports previous assertions that theseare evolutionary sequences involving the continued production andejection of dust. The carbon stars are redder than their oxygen-richcounterparts for the same variability type, except in theF12/F25 ratio, where they are bluer. Of the 28sources in the sample not previous noted to be variable, 18 are clearlyvariable in the DIRBE data, with amplitudes of variation of ~0.9 mag at4.9 μm and ~0.6 mag at 12 μm, consistent with them being verydusty Mira-like variables. We also present individual DIRBE light curvesof a few selected stars. The DIRBE light curves of the semiregularvariable L2 Pup are particularly remarkable. The maxima at1.25, 2.2, and 3.5 μm occur 10-20 days before those at 4.9 and 12μm, and, at 4.9 and 12 μm, another maximum is seen between the twonear-infrared maxima.
| Technetium and the third dredge up in AGB stars. I. Field stars
We searched for Tc in a sample of long period variables selected bystellar luminosity derived from Hipparcos parallaxes. Tc, as an unstables-process element, is a good indicator for the evolutionary status ofstars on the asymptotic giant branch (AGB). In this paper we study theoccurrence of Tc as a function of luminosity to provide constraints onthe minimum luminosity for the third dredge up as estimated from recentstellar evolution models.A large number of AGB stars above the estimated theoretical limit forthe third dredge up are found not to show Tc. We confirm previousfindings that only a small fraction of the semiregular variables show Tclines in their spectra. Contrary to earlier results by Little et al.(\cite{llmb87}) we find also a significant number of Miras without Tc.The presence and absence of Tc is discussed in relation to the massdistribution of AGB stars. We find that a large fraction of the stars ofour sample must have current masses of less than 1.5 Msun .Combining our findings with stellar evolution scenarios we conclude thatthe fraction of time a star is observed as a SRV or a Mira is dependenton its mass.Partly based on observations collected at the European SouthernObservatory, Paranal, Chile (ESO-Programme 65.L-0317(A)).
| Reprocessing the Hipparcos data of evolved stars. III. Revised Hipparcos period-luminosity relationship for galactic long-period variable stars
We analyze the K band luminosities of a sample of galactic long-periodvariables using parallaxes measured by the Hipparcos mission. Theparallaxes are in most cases re-computed from the Hipparcos IntermediateAstrometric Data using improved astrometric fits and chromaticitycorrections. The K band magnitudes are taken from the literature andfrom measurements by COBE, and are corrected for interstellar andcircumstellar extinction. The sample contains stars of several spectraltypes: M, S and C, and of several variability classes: Mira, semiregularSRa, and SRb. We find that the distribution of stars in theperiod-luminosity plane is independent of circumstellar chemistry, butthat the different variability types have different P-L distributions.Both the Mira variables and the SRb variables have reasonablywell-defined period-luminosity relationships, but with very differentslopes. The SRa variables are distributed between the two classes,suggesting that they are a mixture of Miras and SRb, rather than aseparate class of stars. New period-luminosity relationships are derivedbased on our revised Hipparcos parallaxes. The Miras show a similarperiod-luminosity relationship to that found for Large Magellanic CloudMiras by Feast et al. (\cite{Feast-1989:a}). The maximum absolute Kmagnitude of the sample is about -8.2 for both Miras and semi-regularstars, only slightly fainter than the expected AGB limit. We show thatthe stars with the longest periods (P>400 d) have high mass lossrates and are almost all Mira variables.Based on observations from the Hipparcos astrometric satellite operatedby the European Space Agency (ESA \cite{Hipparcos}).Table \ref{Tab:data1} 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/403/993
| How many Hipparcos Variability-Induced Movers are genuine binaries?
Hipparcos observations of some variable stars, and especially oflong-period (e.g. Mira) variables, reveal a motion of the photocentercorrelated with the brightness variation (variability-induced mover -VIM), suggesting the presence of a binary companion. A re-analysis ofthe Hipparcos photometric and astrometric data does not confirm the VIMsolution for 62 among the 288 VIM objects (21%) in the Hipparcoscatalogue. Most of these 288 VIMs are long-period (e.g. Mira) variables(LPV). The effect of a revised chromaticity correction, which accountsfor the color variations along the light cycle, was then investigated.It is based on ``instantaneous'' V-I color indices derived fromHipparcos and Tycho-2 epoch photometry. Among the 188 LPVs flagged asVIM in the Hipparcos catalogue, 89 (47%) are not confirmed as VIM afterthis improved chromaticity correction is applied. This dramatic decreasein the number of VIM solutions is not surprising, since the chromaticitycorrection applied by the Hipparcos reduction consortia was based on afixed V-I color. Astrophysical considerations lead us to adopt a morestringent criterion for accepting a VIM solution (first-kind risk of0.27% instead of 10% as in the Hipparcos catalogue). With this moresevere criterion, only 27 LPV stars remain VIM, thus rejecting 161 ofthe 188 (86%) of the LPVs defined as VIMs in the Hipparcos catalogue.Based on observations from the Hipparcos astrometric satellite operatedby the European Space Agency (ESA 1997).Table 1 is also 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/399/1167
| 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
| Classification of 2.4-45.2 Micron Spectra from the Infrared Space Observatory Short Wavelength Spectrometer
The Infrared Space Observatory observed over 900 objects with the ShortWavelength Spectrometer in full-grating scan mode (2.4-45.2 μm). Wehave developed a comprehensive system of spectral classification usingthese data. Sources are assigned to groups based on the overall shape ofthe spectral energy distribution (SED). The groups include naked stars,dusty stars, warm dust shells, cool dust shells, very red sources, andsources with emission lines but no detected continuum. These groups arefurther divided into subgroups based on spectral features that shape theSED such as silicate or carbon-rich dust emission, silicate absorption,ice absorption, and fine-structure or recombination lines. Caveatsregarding the data and data reduction, as well as biases intrinsic tothe database, are discussed. We also examine how the subgroups relate tothe evolution of sources to and from the main sequence and how thisclassification scheme relates to previous systems. Based on observationswith the Infrared Space Observatory (ISO), a European Space Agency (ESA)project with instruments funded by ESA Member States (especially thePrinciple Investigator countries: France, Germany, Netherlands, andUnited Kingdom) and with the participation of the Institute of Space andAstronautical Science and the National Aeronautics and SpaceAdministration (NASA).
| s-Process Nucleosynthesis in Carbon Stars
We present the first detailed and homogeneous analysis of the s-elementcontent in Galactic carbon stars of N type. Abundances of Sr, Y, Zr(low-mass s-elements, or ls), Ba, La, Nd, Sm, and Ce (high-masss-elements, or hs) are derived using the spectral synthesis techniquefrom high-resolution spectra. The N stars analyzed are of nearly solarmetallicity and show moderate s-element enhancements, similar to thosefound in S stars, but smaller than those found in the only previoussimilar study (Utsumi 1985), and also smaller than those found insupergiant post-asymptotic giant branch (post-AGB) stars. This is inagreement with the present understanding of the envelope s-elementenrichment in giant stars, which is increasing along the spectralsequence M-->MS-->S-->SC-->C during the AGB phase. Wecompare the observational data with recent s-process nucleosynthesismodels for different metallicities and stellar masses. Good agreement isobtained between low-mass AGB star models (M<~3 Msolar)and s-element observations. In low-mass AGB stars, the13C(α, n)16O reaction is the main source ofneutrons for the s-process a moderate spread, however, must exist in theabundance of 13C that is burnt in different stars. Bycombining information deriving from the detection of Tc, the infraredcolors, and the theoretical relations between stellar mass, metallicity,and the final C/O ratio, we conclude that most (or maybe all) of the Nstars studied in this work are intrinsic, thermally pulsing AGB stars;their abundances are the consequence of the operation of third dredge-upand are not to be ascribed to mass transfer in binary systems.
| 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
| The carrier of the ``30'' mu m emission feature in evolved stars. A simple model using magnesium sulfide
We present 2-45 mu m spectra of a large sample of carbon-rich evolvedstars in order to study the ``30'' mu m feature. We find the ``30'' mu mfeature in a wide range of sources: low mass loss carbon stars, extremecarbon-stars, post-AGB objects and planetary nebulae. We extract theprofiles from the sources by using a simple systematic approach to modelthe continuum. We find large variations in the wavelength and width ofthe extracted profiles of the ``30'' mu m feature. We modelled the wholerange of profiles in a simple way by using magnesium sulfide (MgS) dustgrains with a MgS grain temperature different from the continuumtemperature. The systematic change in peak positions can be explained bycooling of MgS grains as the star evolves off the AGB. In severalsources we find that a residual emission excess at ~ 26 mu m can also befitted using MgS grains but with a different grains shape distribution.The profiles of the ``30'' mu m feature in planetary nebulae arenarrower than our simple MgS model predicts. We discuss the possiblereasons for this difference. We find a sample of warm carbon-stars withvery cold MgS grains. We discuss possible causes for this phenomenon. Wefind no evidence for rapid destruction of MgS during the planetarynebula phase and conclude that the MgS may survive to be incorporated inthe ISM. Based on observations obtained with ISO, an ESA project withinstruments funded by ESA Member states (especially the PI countries:France, Germany, The Netherlands and the United Kingdom) with theparticipation of ISAS and NASA. Appendix A (Figs. A.1 and A.2) is onlyavailable in electronic form at http://www.edpsciences.org
| CHARM: A Catalog of High Angular Resolution Measurements
The Catalog of High Angular Resolution Measurements (CHARM) includesmost of the measurements obtained by the techniques of lunaroccultations and long-baseline interferometry at visual and infraredwavelengths, which have appeared in the literature or have otherwisebeen made public until mid-2001. A total of 2432 measurements of 1625sources are included, along with extensive auxiliary information. Inparticular, visual and infrared photometry is included for almost allthe sources. This has been partly extracted from currently availablecatalogs, and partly obtained specifically for CHARM. The main aim is toprovide a compilation of sources which could be used as calibrators orfor science verification purposes by the new generation of largeground-based facilities such as the ESO Very Large Interferometer andthe Keck Interferometer. The Catalog is available in electronic form atthe 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/386/492, and from theauthors on CD-Rom.
| 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.
| 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.
| The 85Kr s-Process Branching and the Mass of Carbon Stars
We present new spectroscopic observations for a sample of C(N)-type redgiants. These objects belong to the class of asymptotic giant branchstars, experiencing thermal instabilities in the He-burning shell(thermal pulses). Mixing episodes called third dredge-up enrich thephotosphere with newly synthesized 12C in the He-rich zone,and this is the source of the high observed ratio between carbon andoxygen (C/O>=1 by number). Our spectroscopic abundance estimatesconfirm that, in agreement with the general understanding of the lateevolutionary stages of low- and intermediate-mass stars, carbonenrichment is accompanied by the appearance of s-process elements in thephotosphere. We discuss the details of the observations and of thederived abundances, focusing in particular on rubidium, a neutrondensity sensitive element, and on the s-elements Sr, Y, and Zr belongingto the first s-peak. The critical reaction branching at 85Kr,which determines the relative enrichment of the studied species, isdiscussed. Subsequently, we compare our data with recent models fors-processing in thermally pulsing asymptotic giant branch stars, atmetallicities relevant for our sample. A remarkable agreement betweenmodel predictions and observations is found. Thanks to the differentneutron density prevailing in low- and intermediate-mass stars,comparison with the models allows us to conclude that most C(N) starsare of low mass (M<~3 Msolar). We also analyze the12C/13C ratios measured, showing that most of themcannot be explained by canonical stellar models. We discuss how thisfact would require the operation of an ad hoc additional mixing,currently called cool bottom process, operating only in low-mass starsduring the first ascent of the red giant branch and, perhaps, alsoduring the asymptotic giant branch.
| Polarimetry of 167 Cool Variable Stars: Data
Multicolor photoelectric polarimetry is presented for 167 stars, most ofwhich are variable stars. The observations constitute a data set thatfor some stars covers a time span of 35 yr. Complex variations are foundover time and wavelength and in both the amount of polarization and itsposition angle, providing constraints for understanding the polarizingenvironments in and around these cool stars.
| Speckle Interferometry of New and Problem Hipparcos Binaries. II. Observations Obtained in 1998-1999 from McDonald Observatory
The Hipparcos satellite made measurements of over 9734 known doublestars, 3406 new double stars, and 11,687 unresolved but possible doublestars. The high angular resolution afforded by speckle interferometrymakes it an efficient means to confirm these systems from the ground,which were first discovered from space. Because of its coverage of adifferent region of angular separation-magnitude difference(ρ-Δm) space, speckle interferometry also holds promise toascertain the duplicity of the unresolved Hipparcos ``problem'' stars.Presented are observations of 116 new Hipparcos double stars and 469Hipparcos ``problem stars,'' as well as 238 measures of other doublestars and 246 other high-quality nondetections. Included in these areobservations of double stars listed in the Tycho-2 Catalogue andpossible grid stars for the Space Interferometry Mission.
| 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).
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Dades d'Observació i Astrometria
| Constel·lació: | Orion |
| Ascensió Recta: | 05h05m23.70s |
| Declinació: | +01°10'39.0" |
| Magnitud Aparent: | 6.17 |
| Distancia: | 214.592 parsecs |
| Moviment propi RA: | 7.5 |
| Moviment propi Dec: | -1.4 |
| B-T magnitude: | 10.777 |
| V-T magnitude: | 6.293 |
Catàlegs i designacions:
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