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Revised classification of the SBS carbon star candidates including the discovery of a new emission line dwarf carbon star
Context. Faint high-latitude carbon stars are rare objects commonlythought to be distant, luminous giants. For this reason, they are oftenused to probe the structure of the Galactic halo; however, more accurateinvestigation of photometric and spectroscopic surveys has revealed anincreasing percentage of nearby objects with luminosities of mainsequence stars. Aims: In the General Catalogue of the SecondByurakan Survey (SBS) only ten objects are indicated as carbon starcandidates. This work aims at clarifying the nature of these stars. Methods: We analyzed new optical spectra and photometry and usedastronomical databases available on the web. Results: We verifiedthat two stars are N-type giants already confirmed by other surveys. Wefound that four candidates are M type stars and confirmed the carbonnature of the remaining four stars; the characteristics of three of themare consistent with an early CH giant type. The fourth candidate,SBS 1310+561 identified with a high proper motionstar, is a rare type of dwarf carbon showing emission lines in itsoptical spectrum. We estimated absolute magnitudes and distances to thedwarf carbon and the three CH stars. Conclusions: Our limitedsample confirmed the increasing evidence that spectroscopy or colouralone are not conclusive luminosity discriminants for CH-type carbonstars.Based on observations made at the 1.52 m telescope of the BolognaObservatory and 1.83 m telescope of the Asiago Observatory.Figures 1, 3,and 5 are available in electronic form at http://www.aanda.orgThe spectra (asciifiles) are only available at CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/532/A69
| The CH fraction of carbon stars at high Galactic latitudes
CH stars form a distinct class of objects with characteristic propertieslike iron deficiency, enrichment of carbon and overabundance of heavyelements. These properties can provide strong observational constraintsfor the theoretical computation of nucleosynthesis at low metallicity.An important issue is the relative surface density of CH stars, whichcan provide valuable input to our understanding of the role of low- tointermediate-mass stars in early Galactic chemical evolution.Spectroscopic characterization provides an effective way of identifyingCH stars. The present analysis aims at a quantitative assessment of thefraction of CH stars in a sample using a set of spectral classificationcriteria. The sample consists of 92 objects selected from a collectionof candidate faint high-latitude carbon stars from the Hamburg/ESOsurvey. Medium-resolution (?/?? ~ 1300) spectra forthese objects were obtained using the Optomechanics Research (OMR)spectrograph at the Vainu Bappu Observatory (VBO), Kavalur and theHimalaya Faint Object Spectrograph (HFOSC) at the Himalayan ChandraTelescope (HCT), Indian Astronomical Observatory, Hanle, during2007-2009, spanning a wavelength range 3800-6800Å. Spectralanalysis shows 36 of the 92 objects to be potential CH stars; combinedwith our earlier studies this implies ~37 per cent (of 243 objects) asthe CH fraction. We present spectral descriptions of the newlyidentified CH star candidates. Estimated effective temperatures,12C/13C isotopic ratios and their locations on thetwo-colour J - H versus H - K plot are used to support theiridentification.
| 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.
| Low-resolution spectroscopy of high Galactic latitude objects: A search for CH stars
Properties of CH stars like iron deficiency and enrichment of carbon andheavy elements can provide valuable inputs to our understanding ofnucleosynthesis. In particular, these parameters provide strongobservational constraints for theoretical studies of nucleosynthesis ofheavy elements at low-metallicity. Accurate identification andspectroscopic characterization of CH stars are therefore very essential.We have undertaken a programme with a prime objective to search forthese objects in a mixed sample of carbon stars taken from HamburggESO survey. The spectra of the objects were obtained using OMR at VBO,Kavalur and HFOSC at HCT, IAO, Hanle, during 2005 and 2006. Here, wereport a detection of twenty-one CH stars from a sample of sixtyobjects based on low-resolution spectral analysis. Estimated effectivetemperatures, ^{12}Cg^{13}C isotopic ratios, and their location in thetwo colour J-H vs H-K plot support their identification with the classof CH stars. Detection of these potential CH star candidates and theirspectral description is the main theme of this paper.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| Tycho-2 stars with infrared excess in the MSX Point Source Catalogue
Stars of all evolutionary phases have been found to have excess infraredemission due to the presence of circumstellar material. To identify suchstars, we have positionally correlated the infrared Mid-Course SpaceExperiment (MSX) Point Source Catalogue and the Tycho-2 opticalcatalogue. Near-mid-infrared colour criteria have been developed toselect infrared excess stars. The search yielded 1938 excess stars; overhalf (979) have never previously been detected by IRAS. The excess starswere found to be young objects such as Herbig Ae/Be and Be stars, andevolved objects such as OH/IR (infrared) and carbon stars. A number ofB-type excess stars were also discovered whose infrared colours couldnot be readily explained by known catalogued objects.
| CH stars at high Galactic latitudes
Carbon-rich stars of Population II, such as CH stars, can provide directinformation on the role of low- to intermediate-mass stars of the haloin early Galactic evolution. Thus accurate knowledge of the CH stellarpopulation is a critical requirement for building up scenarios for earlyGalactic chemical evolution. In the present work, we report on severalCH stars identified in a sample of faint high-latitude carbon stars fromthe Hamburg survey and discuss their medium-resolution spectra coveringthe wavelength range 4000-6800 Å. Estimation of the depths of the(1,0)12C12C λ4737 and(1,0)12C13C λ4744 bands in these starsindicates an isotopic ratio 12C/13C ~ 3, apartfrom a few exceptions; these ratios are consistent with existingtheories of CH stellar evolution. The stars of the Hamburg survey, atotal of 403 objects, were reported to be carbon star candidates withstrong C2 and CN molecular bands. In the first phase ofobservation, we acquired spectra of 91 objects. Inspection of thespectra of those objects shows 51 objects with C2 molecularbands in their spectra, of which 13 stars have low flux below about 4300Å. There are 25 objects that show weak or moderate CH and CNbands, 12 objects that show weak but detectable CH bands, and threeobjects that do not show any molecular bands due to C2, CN orCH in their spectra. Objects with C2 molecular bands and withgood signals bluewards of 4300 Åthat show prominent CH bands intheir spectra are potential candidate CH stars. There were 35 suchcandidates found in the present sample of 91 objects observed so far.The set of CH stars identified could be the targets of subsequentobservation at high resolution for a detailed and comprehensive analysisto understand their role in early Galactic chemical evolution.
| 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
| 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).
| 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 Spectrum Near Maximum Light of the Unusual R Coronae Borealis Variable DY Persei
DY Per was confirmed photometrically as an R CrB variable by Alksnis in1994. Spectra near maximum light show the high-speed ejection of matter(sodium at -174 km/sec in DY Per) characteristic of many of thesevariable stars. Moderate hydrogen deficiency may also be present. DY Peris remarkable in having a temperature many hundreds of degrees lowerthan most of the R CrB variables. It is unusual also in not showingclear spectroscopic evidence of high luminosit. (SECTION: Stars)
| A Moderate-Resolution Spectral Atlas of Carbon Stars: R, J, N, CH, and Barium Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJS..105..419B&db_key=AST
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| Photometry and Radial Velocities of Southern Carbon Stars
Not Available
| A general catalogue of cool carbon stars
Not Available
| Identification Charts for 42 Variable Stars
Not Available
| Note on the autocorrelation analysis of the light curve of the RV Tauri variable R Scuti.
Abstract image available at:http://adsabs.harvard.edu/abs/1957AJ.....62..367K
| Carbon Stars in Two Northern Milky way Zones.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1957ApJ...125..195N&db_key=AST
| Contribution à l'étude des étoiles rouges carbonées II
Not Available
| Radial Velocities of 283 Stars of Spectral Classes R and N.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1944ApJ....99..145S&db_key=AST
| Objects having peculiar spectra.
Not Available
| Stars having peculiar spectra.
Not Available
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