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NSCC—A New Scheme of Classification of C-Rich Stars Devised from Optical and Infrared Observations
A new classification system for carbon-rich stars is presented based onan analysis of 51 asymptotic giant branch carbon stars through the mostrelevant classifying indices available. The extension incorporated,which also represents the major advantage of this new system, is thecombination of the usual optical indices that describe the photospheresof the objects, with new infrared ones, which allow an interpretation ofthe circumstellar environment of the carbon-rich stars. This new systemis presented with the usual spectral subclasses and C2-, j-,MS-, and temperature indices, and also with the new SiC- (SiC/C.A.abundance estimation) and ?- (opacity) indices. The values for theinfrared indices were carried out through a Monte Carlo simulation ofthe radiative transfer in the circumstellar envelopes of the stars. Thefull set of indices, when applied to our sample, resulted in a moreefficient system of classification, since an examination in a widespectral range allows us to obtain a complete scenario for carbon stars.
| AGB variables and the Mira period-luminosity relation
Published data for large-amplitude asymptotic giant branch variables inthe Large Magellanic Cloud (LMC) are re-analysed to establish theconstants for an infrared (K) period-luminosity relation of the formMK = ρ[logP - 2.38] + δ. A slope of ρ = -3.51+/- 0.20 and a zero-point of δ = -7.15 +/- 0.06 are found foroxygen-rich Miras (if a distance modulus of 18.39 +/- 0.05 is used forthe LMC). Assuming this slope is applicable to Galactic Miras we discussthe zero-point for these stars using the revised Hipparcos parallaxestogether with published very long baseline interferometry (VLBI)parallaxes for OH masers and Miras in globular clusters. These result ina mean zero-point of δ = -7.25 +/- 0.07 for O-rich Galactic Miras.The zero-point for Miras in the Galactic bulge is not significantlydifferent from this value.Carbon-rich stars are also discussed and provide results that areconsistent with the above numbers, but with higher uncertainties. Withinthe uncertainties there is no evidence for a significant differencebetween the period-luminosity relation zero-points for systems withdifferent metallicity.
| The Mira variable S Orionis: relationships between the photosphere, molecular layer, dust shell, and SiO maser shell at 4 epochs
Aims:We present the first multi-epoch study that includes concurrentmid-infrared and radio interferometry of an oxygen-rich Mira star. Methods: We obtained mid-infrared interferometry of S Ori withVLTI/MIDI at four epochs in December 2004, February/March 2005, November2005, and December 2005. We concurrently observed v=1, J=1-0 (43.1 GHz),and v=2, J=1-0 (42.8 GHz) SiO maser emission toward S Ori with the VLBAin January, February, and November 2005. The MIDI data are analyzedusing self-excited dynamic model atmospheres including molecular layers,complemented by a radiative transfer model of the circumstellar dustshell. The VLBA data are reduced to the spatial structure and kinematicsof the maser spots. Results: The modeling of our MIDI dataresults in phase-dependent continuum photospheric angular diameters of9.0 ± 0.3 mas (phase 0.42), 7.9 ± 0.1 mas (0.55), 9.7± 0.1 mas (1.16), and 9.5 ± 0.4 mas (1.27). The dust shellcan best be modeled with Al2O3 grains using phase-dependent innerboundary radii between 1.8 and 2.4 photospheric radii. The dust shellappears to be more compact with greater optical depth near visualminimum (?_V˜ 2.5), and more extended with lower optical depthafter visual maximum (?_V˜ 1.5). The ratios of the 43.1GHz/42.8 GHz SiO maser ring radii to the photospheric radii are 2.2± 0.3/2.1 ± 0.2 (phase 0.44), 2.4 ± 0.3/2.3± 0.4 (0.55), and 2.1 ± 0.3/1.9 ± 0.2 (1.15). Themaser spots mark the region of the molecular atmospheric layers justbeyond the steepest decrease in the mid-infrared model intensityprofile. Their velocity structure indicates a radial gas expansion. Conclusions: S Ori shows significant phase-dependences of photosphericradii and dust shell parameters. Al2O3 dust grains and SiO maser spotsform at relatively small radii of ~1.8-2.4 photospheric radii. Ourresults suggest increased mass loss and dust formation close to thesurface near the minimum visual phase, when Al2O3 dust grains areco-located with the molecular gas and the SiO maser shells, and a moreexpanded dust shell after visual maximum. Silicon does not appear to bebound in dust, as our data show no sign of silicate grains.Based on observations made with the Very Large Telescope Interferometer(VLTI) at the Paranal Observatory under program IDs 074.D-0075 and076.D-0338. Based on observations made with the Very Long Baseline Array(VLBA) under project BB192. The VLBA is operated by the National RadioAstronomy Observatory (NRAO). The National Radio Astronomy Observatoryis a facility of the National Science Foundation operated undercooperative agreement by Associate Universities, Inc. Tables A.1-A.4 areonly available 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/470/191 Color versions ofFigs. 2-8, 10, and 11 are available in electronic form viahttp://www.aanda.org
| Temporal variations of the outer atmosphere and the dust shell of the carbon-rich Mira variable V Ophiuchi probed with VLTI/MIDI
Aims.We present the first multi-epoch N-band spectro-interferometricobservations of the carbon-rich Mira variable V Ophusing MIDI at the ESO's Very Large Telescope Interferometer. Our aim isto study temporal variations of physical properties of the outeratmosphere and the circumstellar dust shell based onspectrally-dispersed N-band visibilities over the C2H2 (+HCN) featuresand the dust emission. Methods: Our MIDI observations werecarried out at three different phases 0.18, 0.49, and 0.65, with threedifferent baselines (projected baseline lengths of 42-124 m) using four8.2 m Unit Telescopes (UT2-UT4, UT1-UT4, and UT2-UT3 baselineconfigurations). Results: The wavelength dependence of theuniform-disk diameters obtained at all epochs is characterized by aroughly constant region between 8 and 10 μm with a slight dipcentered at 9.5 μm and a gradual increase longward of 10 μm.These N-band angular sizes are significantly larger than the estimatedphotospheric size of V Oph. The angular sizes observed at differentepochs reveal that the object appears smaller at phase 0.49 (minimumlight) with uniform-disk diameters of 5-12 mas than at phases 0.18 (12-20 mas) and 0.65 ( 9-15 mas). We interpret these results with a modelconsisting of optically thick C2H2 layers and an optically thin dustshell. Our modeling suggests that the C2H2 layers around V Oph are moreextended ( 1.7-1.8 Rstar) at phases 0.18 and 0.65 than atphase 0.49 ( 1.4 Rstar) and that the C2H2 column densitiesappear to be the smallest at phase 0.49. We also find that the dustshell consists of amorphous carbon and SiC with an inner radius of 2.5Rstar, and the total optical depths of τV ≈0.6-0.9 (τ11.3 μm ≈ 0.003 and 0.004 for amorphouscarbon and SiC, respectively) found at phases 0.18 and 0.65 are higherthan the value obtained at phase 0.49, τV ≈ 0.3(τ11.3 μm ≈ 0.001 and 0.002 for amorphous carbonand SiC, respectively). Conclusions: Our MIDI observations andmodeling indicate that carbon-rich Miras also have extended layers ofpolyatomic molecules as previously confirmed in oxygen-rich Miras. Thetemporal variation of the N-band angular size is largely governed by thevariations of the opacity and the geometrical extension of the C2H2layers and the dust shell, and consequently, this masks the sizevariation of the photosphere. Also, the observed weakness of themid-infrared C2H2 absorption in carbon-rich Miras can be explained bythe emission from the extended C2H2 layers and the dust shell.Based on observations made with the Very Large Telescope Interferometerof the European Southern Observatory. Program ID: 075.D-0607. Table 4 isonly available 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/466/1099
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| Carbon-rich Mira variables: kinematics and absolute magnitudes
The kinematics of Galactic C-Miras are discussed on the basis of thebolometric magnitudes and radial velocities of Papers I and II of thisseries. Differential Galactic rotation is used to derive a zero-pointfor the bolometric period-luminosity relation which is in satisfactoryagreement with that inferred from the Large Magellanic Cloud (LMC)C-Miras. We find for the Galactic Miras, Mbol = -2.54 logP +2.06(+/-0.24), where the slope is taken from the LMC. The mean velocitydispersion, together with the data of Nordström et al. and thePadova models, leads to a mean age for our sample of C-Miras of 1.8 +/-0.4Gyr and a mean initial mass of 1.8 +/- 0.2 Msolar.Evidence for a variation of velocity dispersion with period is found,indicating a dependence of period on age and initial mass, the longerperiod stars being younger. We discuss the relation between the O- andC-Miras and also their relative numbers in different systems.
| Carbon-rich Mira variables: radial velocities and distances
Optical radial velocities have been measured for 38 C-type Miravariables (C-Miras). These data together with others in the literatureare used to study the differences between optical and CO millimetre (mm)observations for C-Miras and the necessary corrections to the opticalvelocities are derived in order to obtain the true radial velocities ofthe variables. The difference between absorption and emission-linevelocities is also examined. A particularly large difference (+30kms-1) is found in the case of the Hα line. A catalogue isgiven of 177 C-Miras with estimated distances and radial velocities. Thedistances are based on bolometric magnitudes derived in Paper I usingSouth African Astronomical Observatory (SAAO) observations or (for 60 ofthe stars) using non-SAAO photometry. In the latter case, the necessarytransformations to the SAAO system are derived. These data will be usedin Paper III to study the kinematics of the C-Miras.
| Near-infrared photometry of carbon stars
Near-infrared, JHKL, photometry of 239 Galactic C-rich variable stars ispresented and discussed. From these and published data, the stars wereclassified as Mira or non-Mira variables, and amplitudes and pulsationperiods, ranging from 222 to 948 d for the Miras, were determined formost of them. A comparison of the colour and period relations with thoseof similar stars in the Large Magellanic Cloud indicates minordifferences, which may be the consequence of sample selection effects.Apparent bolometric magnitudes were determined by combining the meanJHKL fluxes with mid-infrared photometry from IRAS and MSX. Then, usingthe Mira period luminosity relation to set the absolute magnitudes,distances were determined - to greater accuracy than has hitherto beenpossible for this type of star. Bolometric corrections to the Kmagnitude were calculated and prescriptions derived for calculatingthese from various colours. Mass-loss rates were also calculated andcompared to values in the literature.Approximately one-third of the C-rich Miras and an unknown fraction ofthe non-Miras exhibit apparently random obscuration events that arereminiscent of the phenomena exhibited by the hydrogen-deficient RCoronae Borealis stars. The underlying cause of this is unclear, but itmay be that mass loss, and consequently dust formation, is very easilytriggered from these very extended atmospheres.Based on observations made at the South African AstronomicalObservatory.E-mail: paw@saao.ac.za
| The mid- and far-infrared colours of AGB and post-AGB stars
With the advent of space missions, like SPITZER and ASTRO-F, withsensitive detectors in the near- and mid-infra red covering a reasonablefield-of-view and having a good spatial resolution, it will be possibleto detect individual AGB stars in Local Group galaxies. The filters usedby these missions are non-standard and different from mission tomission. In this paper, the colours of mass-losing AGB and post-AGBstars are calculated in the broad-band filters of the SPITZER andASTRO-F missions, as well as Bessell V,I and 2MASS J,H,K to connectthese results to existing ground-based data. The models are calculatedfor carbon- and oxygen-rich chemistry and cover different effectivetemperatures and dust compositions.
| Proposal of observational program of CCD monitoring of 30 carbon Miras in V, R and I
We present a new long-term observational program of CCD monitoring of 30selected carbon Miras (V 374 Aql, S Aur, UV Aur, AU Aur, AZ Aur, S Cam,R CMi, W Cas, X Cas, HV Cas, S Cep, V CrB, U Cyg, V Cyg, RS Cyg, WX Cyg,T Dra, R For, VX Gem, ZZ Gem, V Hya, CZ Hya, R Lep, U Lyr, CL Mon, VOph, RZ Peg, SY Per, RU Vir, SS Vir) in the standard V, RC and I Johnsonian filters. The aim of the program is to reveal and describephotometric behavior of above mentioned objects and to ascertain thereliability of visual observations of these variable stars. The authorswill send interested persons the pertinent finding charts and they willsee to process rough CCD exposures taken in desired colors themselves.
| Secular Evolution in Mira Variable Pulsations
Stellar evolution theory predicts that asymptotic giant branch (AGB)stars undergo a series of short thermal pulses that significantly changetheir luminosity and mass on timescales of hundreds to thousands ofyears. These pulses are confirmed observationally by the existence ofthe short-lived radioisotope technetium in the spectra of some of thesestars, but other observational consequences of thermal pulses are subtleand may only be detected over many years of observations. Secularchanges in these stars resulting from thermal pulses can be detected asmeasurable changes in period if the star is undergoing Mira pulsations.It is known that a small fraction of Mira variables exhibit largesecular period changes, and the detection of these changes among alarger sample of stars could therefore be useful in evolutionary studiesof these stars. The American Association of Variable Star Observers(AAVSO) International Database currently contains visual data for over1500 Mira variables. Light curves for these stars span nearly a centuryin some cases, making it possible to study the secular evolution of thepulsation behavior on these timescales. In this paper we present theresults of our study of period change in 547 Mira variables using datafrom the AAVSO. We use wavelet analysis to measure the period changes inindividual Mira stars over the span of available data. By making linearfits to the period versus time measurements, we determine the averagerates of period change, dlnP/dt, for each of these stars. We findnonzero dlnP/dt at the 2 σ significance level in 57 of the 547stars, at the 3 σ level in 21 stars, and at the level of 6 σor greater in eight stars. The latter eight stars have been previouslynoted in the literature, and our derived rates of period change largelyagree with published values. The largest and most statisticallysignificant dlnP/dt are consistent with the rates of period changeexpected during thermal pulses on the AGB. A number of other starsexhibit nonmonotonic period change on decades-long timescales, the causeof which is not yet known. In the majority of stars, the periodvariations are smaller than our detection threshold, meaning theavailable data are not sufficient to unambiguously measure slowevolutionary changes in the pulsation period. It is unlikely that morestars with large period changes will be found among heretoforewell-observed Mira stars in the short term, but continued monitoring ofthese and other Mira stars may reveal new and serendipitous candidatesin the future.
| Atlas of Hα emission lines and V light curves of 30 carbon Miras
This paper presents an atlas of V light curves and Hα emissionlines of 30 carbon Miras observed in various photometrical phases. Thevisualization of both photometric and spectral variations allowed us toreveal a strong correlation between the equivalent widths of theHα emission of carbon Miras and their V brightnesses as a functionof the photometric phase.
| 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
| Letter to the Editor: Brighter Maxima of 30 Selected Mira-Type Variable Stars for the Period 1978-1977
Letter to the Editor
| 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
| 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
| 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
| High Angular Resolution Observations of Late-Type Stars
This paper presents speckle observations of Mira (o Cet) and late-typestars with the PISCO speckle camera of Pic du Midi during the period1995-1998. A survey for binarity among a sample of late-type stars wasperformed, which led to seven positive detections out of 36 objects.Photometric and color variations of the companion of Mira were searchedfor, but no significant brightness variations could be found over atimescale of ~5-10 minutes. The position and photometry measurements,the restored images with high angular resolution of the binary systemMira A-B (ADS 1778) are in full agreement with Hubble Space Telescopedata obtained at the same epoch. A new orbit has been derived for MiraA-B.
| 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.
| 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
| 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.
| Infrared colours for Mira-like long-period variables found in the (Mȯ<~10-7 Msolar yr-1) Hipparcos Catalogue
Near-infrared, JHKL, photometry is presented for 193 Mira andsemi-regular variables that were observed by Hipparcos; periods,bolometric magnitudes and amplitudes are derived for 92 of them. Becauseof the way in which the Hipparcos targets were selected, this group ofstars provides a useful data base of Miras with low mass-loss rates(Mȯ<~10-7Msolaryr-1).Various period-colour relationships are discussed in detail. The colour,particularly BCK = 10.86 - 38.10 K (J - K)0 +64.16(J - K)20 - 50.72(J -K)30 + 19, K-L, at a given period is found todepend on the pulsation amplitude of the star. A comparison with modelssuggests that this is a consequence of atmospheric extension, in thesense that large-amplitude pulsators have very extended atmospheres andredder Mȯ<10-7Msolaryr-1, K-L and H-K but bluerJ-H than their lower amplitude counterparts. The stars with veryextended atmospheres also have higher values of K-[12] and hence highermass-loss rates. This finding provides further evidence for the causalconnection between pulsation and mass loss. Two sequences are identifiedin the Hp-K versus logP diagram (where Hp is the Hipparcos broad-bandmagnitude) at short periods (logP<2.35). At a given period these twogroups have, on average, the same pulsation amplitude, but differentJHKL colours and spectral types. The short-period stars in the bluersequence have similar near-infrared colours to the Miras found inglobular clusters. Long-term trends in the infrared light curves arediscussed for stars that have sufficient data.
| A library of 0.5 to 2.5 mu m spectra of luminous cool stars
We present a library of 0.5-2.5 mu m digital spectra of cool, mostlyvariable, giant and supergiant stars which should be useful for spectralsynthesis applications, as well as for comparison with theoretical modelatmosphere calculations. The library includes carbon stars, GalacticBulge and Magellanic Cloud stars, and OH/IR stars. The stars observedcover a range of metallicities and masses. Most variable objects wereobserved several times, at different phases of their pulsation cycle. Wediscuss the effects of various fundamental parameters and of variabilityon the spectra. Based on period-luminosity relations and stellarevolutionary tracks, we tentatively assign initial masses to eachobject.
| Trend analysis of 51 carbon long-period variables.
Not Available
| On the distance and mass-loss rate of carbon stars showing the silicon carbide emission feature
The distances and the mass-loss rates of carbon stars are in generalvery poorly known. The various estimates of the distances, taken fromthe general literature, show considerable discrepancies, while theevaluations of the mass-loss rates can be in error by more than an orderof magnitude. In this work we have evaluated these two important stellarparameters for a previously selected sample of 55 carbon stars showingthe 11.3 mu m band, commonly attributed to silicon carbide (SiC) grains.To perform the calculation we have used the values of geometrical andphysical parameters of these sources obtained from the best fits oftheir observed spectra. Using the distance values derived in this wayand the 11.3 mu m band intensity, we have evaluated the absolute bandstrength and we have found that, in agreement with other authors, thereis a correlation between this quantity and the mass-loss rate. Thiscorrelation can be very useful to determine the mass-loss rate of othercarbon stars not included in our sample, by means of the intensity ofthe SiC band, without using the usual technique based on COobservations. The same procedure can be conveniently applied to the sameas well as to other carbon stars, whose spectra will be available to thecommunity in the next future (i.e. the infrared spectra of sourcesobserved by the Infrared Satellite Observatory, ISO).
| Millimeter and some near infra-red observations of short-period Miras and other AGB stars
Millimeter observations of 48 oxygen- and 20 carbon-rich AGB Miras withperiods shorter than 400 days are presented. In addition, observationsof 14 O-rich and 15 C-stars with longer, or no known, periods have alsobeen obtained. The detection statistics is as follows: in12CO J=1-0 and 2-1 we observed 97 stars, and detected 66 inat least one line. We find 24 new detections in the 1-0 line, 38 newdetections in the 2-1 line, and 29 stars have been detected for thefirst time in one or both lines. In 12CO J=3-2 we observed 14stars and detected 11, with 4 new detections. In 13CO J=2-1,3-2 we observed 2 stars and had one new detection. In HCN(1-0) weobserved 5 carbon stars and detected 3, one new. In SO(6_5-5_4) weobserved the same 5 stars and detected none. In CS(3-2) we observed 8carbon stars and detected 3, all new. In SiO(3-2, v=0) we observed 34O-rich stars and detected 25, all new except one. Near-infrared JHKphotometry is presented for seven stars. For four stars it is the firstNIR data published. The luminosity and dust mass loss rate are obtainedfor seven very red stars with unknown pulsation period from modellingthe spectral energy distribution (SED) and IRAS LRS spectra. Thereby, anew IR supergiant is confirmed (AFGL 2968). For the rest of the sample,luminosity and distance are obtained in a variety of ways: usinghipparcos parallaxes, period-luminosity and period-M_K-relationscombined with apparent K magnitudes, and kinematic distances. The dustmass loss rate is obtained from model fitting of the SED (either fromthe literature, or presented in the present paper), or from the observedIRAS 60 mu m flux, corrected for the photospheric contribution. The gasmass loss rate is derived from the observed CO line intensities, aspresented here, combined with existing literature data, if any. Thisallows the derivation of the dust-to-gas ratio. Our and literature CO J= 3-2 data has been used to calibrate the relation between mass lossrate and peak intensity of the CO(3-2) line. Diagrams showing mass lossrate, dust-to-gas ratio and expansion velocity versus pulsation periodare presented. Our observations confirm the existence of an upper limitfor the expansion velocity of C- and O-rich stars, and that this maximumis larger for C-stars, as predicted by the theory of radiation pressureon dust particles. The James Clerk Maxwell Telescope is operated by theObservatories on behalf of the Science and Engineering Council of theUK, the Netherlands Organization for Scientific Research, and theNational Research Council of Canada. Based on observations made with theCarlos Sanchez telescope operated on the island of Tenerife in theSpanish Observatorio del Teide of the Instituto de Astrof\'\i sica deCanarias. Based on observations collected at the European SouthernObservatory, La Silla, Chile within programs ESO 57.E-0105, 59.E-0198and 61.E-0254. Based on data from the ESA Hipparcos astrometrysatellite.
| Dust extinction and intrinsic SEDs of carbon-rich stars. III. The Miras, CS, and SC stars
The present work is an extension of a recent study by Knapik &Bergeat (\cite{knapik97}), and Bergeat et al. (\cite{berge98b})henceforth called Papers I and II, respectively. The spectral energydistributions (SEDs) of about 440 carbon-rich stars and the interstellarextinction observed on their line of sights were analysed. The methodsoriginally developed for Semi-Regular (SR) and Irregular (L) variables(Paper I: our groups CV1 to CV6) were then extended (Paper II) to thehot carbon (HC) stars (our groups HC0 to HC5) and related objects (RCB,BaII and HdC stars). Shortly, this is a kind of a pair method making usesimultaneously of the whole SED from UV to IR. Our approach is appliedhere to the galactic cool carbon-rich variables which were notconsidered in Paper I, namely the carbon Miras and very cool non-Miras,and the CS and SC variables. The carbon Miras with infrared silicateemission are also studied. The photometric CV1 to CV6 classificationscheme of paper I is implemented, and we add here a later CV7-group anda specific SCV-group which corresponds to spectroscopic SC stars. Acontinuous S-SC-CS-C sequence is clearly supported by our results. Thecarbon stars with IR silicate emission included in our study do havecarbon-rich SEDs of the three consecutive groups HC5, CV1 and CV2. Theystand among the relatively hot carbon variables, in the 3600-3000 Krange in effective temperature. The carbon Miras are satisfactorilydescribed in this enlarged scheme. No specific extension is requiredsince non-Miras are also found in the CV7 and SCV-groups. The derivedgroup is however frequently phase-dependent in these large amplitudevariables. Additional selective extinction of circumstellar (CS) originis observed in variable amounts. The mean extinction law for theinterstellar diffuse medium as tabulated by Mathis (\cite{mathis}) isshown to be relevant. It applies to both interstellar and circumstellarextinction with a possible CS neutral extinction in addition which wouldremain undetected here. The corresponding colour excess E(B-V) is largerat minimum light or intermediate phases than what it is at maximum light(where it can amount to zero). It is associated to large IR excessesattributed to the emission from CS dust. Long-term variations onthousands of days may be interpreted in terms of varying CS dust opacityon the line of sight. The dust influence is discussed. It is shown thatscattering, if substantial on the line of sight in the observing lobe,has to be essentially wavelength-independent, i.e. due to large neutralscatterers, especially in high opacity objects like IRC +10216. Finally,with the HC0 to HC5 classification of HC stars (Paper II), we obtain afourteen groups sequence (HC0 to HC5 and then CV1 to CV7 from theearlier one to the latest one, and SCV for SC stars apart). The numberof studied stars amounts now to about 600 that is about 40 stars pergroup on the average when the oxygen-type SEDs are subtracted. Theeffective temperature calibration of this classification scheme iscurrently in preparation. This research has made use of the Simbaddatabase operated at CDS, Strasbourg, France.}\fnmsep\thanks{Partiallybased on data from the ESA HIPPARCOS astrometrysatellite}\fnmsep\thanks{Table~5 is only available in electronic form atthe CDS via anonymous ftp 130.79.128.5
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Osservazione e dati astrometrici
| Costellazione: | Ofiuco |
| Ascensione retta: | 16h26m43.70s |
| Declinazione: | -12°25'35.8" |
| Magnitudine apparente: | 8.137 |
| Distanza: | 273.973 parsec |
| Moto proprio RA: | -4 |
| Moto proprio Dec: | 6.5 |
| B-T magnitude: | 13.756 |
| V-T magnitude: | 8.601 |
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