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AKARI's infrared view on nearby stars. Using AKARI infrared camera all-sky survey, 2MASS, and Hipparcos catalogs
Context. The AKARI, a Japanese infrared space mission, has performed anAll-Sky Survey in six infrared-bands from 9 to 180 ?m with higherspatial resolutions and better sensitivities than IRAS. Aims: Weinvestigate the mid-infrared (9 and 18 ?m) point source catalog (PSC)obtained with the infrared camera (IRC) onboard AKARI, in order tounderstand the infrared nature of the known objects and to identifypreviously unknown objects. Methods: Color-color diagramsand a color-magnitude diagram were plotted with the AKARI-IRC PSCand other available all-sky survey catalogs. We combined the Hipparcosastrometric catalog and the 2MASS all-sky survey catalog with theAKARI-IRC PSC. We furthermore searched literature and SIMBADastronomical database for object types, spectral types, and luminosityclasses. We identified the locations of representative stars and objectson the color-magnitude and color-color diagram schemes. Theproperties of unclassified sources can be inferred from their locationson these diagrams. Results: We found that the (B-V) vs.(V-S9W) color-color diagram is useful for identifying thestars with infrared excess emerged from circumstellar envelopes ordisks. Be stars with infrared excess are separated well from other typesof stars in this diagram. Whereas (J-L18W) vs. (S9W-L18W)diagram is a powerful tool for classifying several object types.Carbon-rich asymptotic giant branch (AGB) stars and OH/IR stars formdistinct sequences in this color-color diagram. Young stellarobjects (YSOs), pre-main sequence (PMS) stars, post-AGB stars, andplanetary nebulae (PNe) have the largest mid-infrared color excess andcan be identified in the infrared catalog. Finally, we plot the L18W vs.(S9W-L18W) color-magnitude diagram, using the AKARI data togetherwith Hipparcos parallaxes. This diagram can be used to identify low-massYSOs and AGB stars. We found that this diagram is comparable to the [24]vs. ([8.0]-[24]) diagram of Large Magellanic Cloud sources usingthe Spitzer Space Telescope data. Our understanding of Galactic objectswill be used to interpret color-magnitude diagram of stellar populationsin the nearby galaxies that Spitzer Space Telescope observed. Conclusions: Our study of the AKARI color-color andcolor-magnitude diagrams will be used to explore properties ofunknown objects in the future. In addition, our analysis highlights afuture key project to understand stellar evolution with a circumstellarenvelope, once the forthcoming astronometrical data with GAIA areavailable.Catalog (full Tables 3 and 4) are only 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/514/A2
| The chemical composition of carbon stars. The R-type stars
Aims. The aim of this work is to shed some light on the problem of theformation of carbon stars of R-type from a detailed study of theirchemical composition. Methods: We use high-resolution and highsignal-to-noise optical spectra of 23 R-type stars (both early- andlate-types) selected from the Hipparcos catalogue. The chemical analysisis made using spectral synthesis in LTE and state-of-the-art carbon-richspherical model atmospheres. We derive their CNO content (including the12C/13C ratio), average metallicity, lithium, andlight (Sr, Y, Zr) and heavy (Ba, La, Nd, Sm) s-element abundances. Theobserved properties of the stars (galactic distribution, kinematics,binarity, photometry and luminosity) are also discussed. Results:Our analysis shows that late-R stars are carbon stars with identicalchemical and observational characteristics as the normal (N-type) AGBcarbon stars. The s-element abundance pattern derived can be reproducedby low-mass AGB nucleosynthesis models where the 13C(?,n)16O reaction is the main neutron donor. We confirm theresults of the sole previous abundance analysis of early-R stars, namelythat they are carbon stars with near solar metallicity showing enhancednitrogen, low 12C/13C ratios and no s-elementenhancements. In addition, we have found that early-R stars have Liabundances larger than expected for post RGB tip giants. We also findthat a significant number (~40%) of the early-R stars in our sample arewrongly classified, probably being classical CH stars and normal Kgiants. Conclusions: On the basis of the chemical analysis, weconfirm the previous suggestion that late-R stars are just misclassifiedN-type carbon stars in the AGB phase of evolution. Their photometric,kinematic, variability and luminosity properties are also compatiblewith this. In consequence, we suggest that the number of true R stars isconsiderably lower than previously believed. This alleviates the problemof considering R stars as a frequent stage in the evolution of low-massstars. We briefly discuss the different scenarios proposed for theformation of early-R stars. The mixing of carbon during an anomalousHe-flash is favoured, although no physical mechanism able to triggerthat mixing has been found yet. The origin of these stars still remainsa mystery.
| Do Hydrogen-Deficient Carbon Stars have Winds?
We present high resolution spectra of the five known hydrogen-deficientcarbon (HdC) stars in the vicinity of the 10830 Å line of neutralhelium. In R Coronae Borealis (RCB) stars the He I line is known to bestrong and broad, often with a P Cygni profile, and must be formedin the powerful winds of those stars. RCB stars have similar chemicalabundances as HdC stars and also share greatly enhanced 18Oabundances with them, indicating a common origin for these two classesof stars, which has been suggested to be white dwarf mergers. A narrowHe I absorption line may be present in the hotter HdC stars, but no lineis seen in the cooler stars, and no evidence for a wind is found in anyof them. The presence of wind lines in the RCB stars is stronglycorrelated with dust formation episodes so the absence of wind lines inthe HdC stars, which do not make dust, is as expected.
| The chemical composition of R-stars
The preliminary results of the chemical analysis of a sample of 22galactic R-stars with measured parallaxes are presented. We have derivedthe C/O and 12C/13C ratios, the averagemetallicity ([M/H]) and the Li abundances. We find that most of thestars have 12C/13C below 20 with nosignificant difference between cool and hot R-stars. The C/O ratioranges between 1 to 2. We obtain a clear separation in the Liabundance between hot and cool R stars, with a mean value of log epsilon(Li) = +0.90 and log epsilon (Li) =-0.50, respectively. Cool stars areof near solar metallicity whereas hot stars show a larger spread,-0.5< [Fe/H] < +0.1. Concerning the possibility of s-elementenhancements, we obtain [Rb/M] > 0 in seven hot stars and in three ofthem (R-hot) the analysis of the 5924 {Å} TcI line might becompatible with Tc detection. However, the detection of other s-elementenhancements is necessary to elucidate the evolutionary stage of thesecarbon stars of which origin is still unknown.
| 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
| Reprocessing the Hipparcos data for evolved giant stars II. Absolute magnitudes for the R-type carbon stars
The Hipparcos Intermediate Astrometric Data for carbon stars have beenreprocessed using an algorithm which provides an objective criterion forrejecting anomalous data points and constrains the parallax to bepositive. New parallax solutions have been derived for 317 cool carbonstars, mostly of types R and N. In this paper we discuss the results forthe R stars. The most important result is that the early R stars (i.e.,R0 - R3) have absolute magnitudes and V-K colors locating them among redclump giants in the Hertzsprung-Russell diagram. The average absolutemagnitude MK for early R-type stars (with V - K < 4) hasbeen derived from a Monte-Carlo simulation implicitly incorporating allpossible biases. It appears that the simulated magnitude distributionfor a population with a true Gaussian distribution of mean MK= -2.0 and intrinsic standard deviation 1.0 mag provides a satisfactorymatch to the observed distribution. These values are consistent with theaverage absolute magnitude MK = -1.6 for clump red giants inthe solar neighborhood (Alves 2000). Further, early R-type stars arenon-variable, and their infrared photometric properties show that theyare not undergoing mass loss, properties similar to those of the redclump giants. Stars with subtypes R4 - R9 tend to be cooler and havesimilar luminosity to the N-type carbon stars, as confirmed by theirposition in the (J-H, H-K) color-color diagram. The sample of earlyR-type stars selected from the Hipparcos Catalogue appears to beapproximately complete to magnitude K0 ~ 7, translating intoa completeness distance of 600 pc if all R stars had MK= -2(400 pc if MK= -1). With about 30 early R-type stars in thatvolume, they comprise about 0.04% (0.14% for MK= -1) of thered clump stars in the solar neighborhood. Identification with the redclump locates these stars at the helium core burning stage of stellarevolution, while the N stars are on the asymptotic giant branch, wherehelium shell burning occurs. The present analysis suggests that for asmall fraction of the helium core burning stars (far lower than thefraction of helium shell-burning stars), carbon produced in the interioris mixed to the atmosphere in sufficient quantities to form a carbonstar. Based on observations from the Hipparcos astrometric satelliteoperated by the European Space Agency (ESA 1997).
| 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.
| The Role of Binaries in the Carbon Stars Pheonomenon
Not Available
| Absolute magnitudes of carbon stars from HIPPARCOS parallaxes
Hipparcos trigonometric parallaxes and photometric data for about 40bright carbon stars have been analysed. Individual absolute visual andbolometric magnitudes, normal color indices (B-V)_0, absorption valuesand distance moduli were determined. By comparison with stellarevolutionary tracks for initial mass 1<= M/M_ȯ<=4 it is foundthat the majority of CH- and R-stars are on the giant and subgiantbranches, but N-stars occupy a region -4
| Carbon Stars
Absolute magnitudes are estimated for carbon stars of various subtypesin the Hipparcos catalogue and as found in the Magellanic Clouds.Stellar radii fall within the limits of 2.4-4.7 AU. The chemicalcomposition of carbon stars indicates that the C-N stars show nearlysolar C/H, N/H, and ^12C/^13C ratios. This indicates that much of the Cand N in our Galaxy came from mass-losing carbon stars. Special carbonstars such as the C-R, C-H, and dC stars are described. Mass loss fromasymptotic giant branch (AGB) carbon stars, at rates up to several x10^-5 M{solar} year^-1, contributes about half of the total mass returnto the interstellar medium. R stars do not lose mass and may becarbon-rich red giants. The mass loss rates for Miras are about 10 timeshigher than for SRb and Lb stars, whose properties are similar enough toshow that they are likely to belong to the same population. Thedistribution of carbon star mass loss rates peaks at about 10^-7M{solar} year^-1, close to the rate of growth of the core mass anddemonstrative of the close relationship between mass loss and evolution.Infrared spectroscopy shows that dust mixtures can occur. Detachedshells are seen around some stars; they appear to form on the timescales of the helium shell flashes and to be a normal occurrence incarbon star evolution.
| The R Stars: Carbon Stars of a Different Kind
After $\sim$16 years of radial-velocity observations of a sample of 22R-type carbon stars, no evidence for binary motion has been detected inany of them. This is surprising considering that approximately 20\% ofnormal late-type giants are spectroscopic binaries, and the fraction isclose to 100\% in barium, CH, and subgiant/dwarf CH and barium stars. Itis suggested, therefore, that a process that has caused the mixing ofcarbon to the surface of these stars cannot act in a wide binary system.Possibly, the R stars were once all binaries, but with separations thatwould not allow them to evolve completely up the giant and asymptoticgiant branchs without coalescing. This coalescence may be the agentwhich causes carbon produced in the helium-core flash to be mixedoutwards to a region where convection zones can bring it to the surfaceof the star. (SECTION: Stars)
| A general catalogue of cool carbon stars
Not Available
| Photoelectric photometry of carbon and barium stars in the Vilnius seven-color system and their color excesses
Not Available
| Infrared flux excesses of the warm carbon stars
Infrared photometry of 31 stars having enhanced atmospheric carbonabundances (types R, CH, Ba II) has been obtained to test for thepresence of circumstellar dust emission reported by others. Supplementedby published ground-based and IRAS photometry, energy distributionsspanning the range 0.33-100 microns have been examined. No new excesseslarge enough to be ascribed to the presence of dust having T = 1000-1500K have been found in this survey of warm carbon stars. Some marginalevidence exists for the presence of warm (T = 300 K) dust associatedwith two stars. One star, BD + 17 deg 3325, earlier reported to haveexcess emission at 3.5 microns, has been shown to have no substantailflux excess at wavelengths as long as 4.6 microns, and perhaps 10.2microns. The distinctive colors of carbon-rich stars are found to becaused by increased line blanketing relative to the ordinary giants, andnot due to circumstellar dust emission.
| Ultraviolet spectra and chromospheres of R stars
Long-wavelength IUE spectra of 13 normal R stars and twohydrogen-deficient R0 supergiants were obtained. Early R stars are notedto have line spectra and levels of flux in the ultravioletcharacteristic of G5-K2 III stars, whereas late R stars were observed tohave colors and line spectra similar to late K and M stars, but withgreatly enhanced strength of low-lying multiplets of neutral metals.Hydrogen-deficient carbon stars show readily apparent differences fromthe normal early R stars, reflecting their luminosity and somewhathigher temperatures. The lines of neutral metals in these stars areweakened, while those of ionized metals are strengthened.
| The chemical composition and evolutionary state of the early stars
Using moderate to high-resolution data from the visible, near-infrared,and infrared, abundance analyses have been performed on a sample of 11R0-R5 stars in order to determine the general metallicity (Fe and Ti),any enhancement of s-process elements, the isotopic ratio C-12/C-13, andthe abundances of C, N, and O. The iron abundance of 10 stars is nearlysolar, and the s-process elements have no demonstrable enhancement inthe sample. A 0.7 dex enhancement of carbon relative to the G-K giantsis found in eight stars, while nitrogen is enhanced by a small amount.Oxygen has nearly the value found in the sun, while the C-12/C-13 ratioindicates an enrichment of C-13 with respect to the majority of faintstars. A discussion of the evolutionary state of the class of early Rstars based on these results is presented.
| A composite Hertzsprung-Russell diagram for the peculiar red giants
A composite H-R diagram for the peculiar red giants of the diskpopulation is constructed using the available data for stars of types R,N, S, SC, MS, and Ba, along with theoretical evolutionary tracks. The N,S, SC, and MS stars approximately coincide with the sequence of normal Mgiants in the H-R diagram and can be identified with thehelium-shell-flash phase of evolution. The early R stars and most Bastars occupy the same region of the H-R diagram as normal K giants; thepositions of these stars cannot be reconciled with currentstellar-evolution calculations.
| Ca II H and K reversals in carbon stars.
Abstract image available at:http://adsabs.harvard.edu/abs/1975ApJ...197..611R
| A general catalogue of cool carbon stars
Not Available
| Infra-red photometry of R Coronae borealis type variables and relatedobjects.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1973MNRAS.161..293F&db_key=AST
| Some Intrinsic Properties of Carbon Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1971ApJ...167..521R&db_key=AST
| The use of UBVR photometry for the discovery of peculiar stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970AJ.....75..169M&db_key=AST
| The magnitudes, colors and motions of stars of spectral class R.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1958AJ.....63..477V&db_key=AST
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