Statistics of Carbon Stars in the Galaxy
Omar Kurtanidze2000, Symposium - International Astronomical Union
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Carbon Stars at High Galactic Latitude
Photometry and kinematics are presented for a sample of objective prism selected carbon stars towards the north and south Galactic poles. Distances are determined by fitting the infrared colors to a giant branch. If these stars are like the carbon stars seen in dwarf spheroidal galaxies, the median distance of the sample is 28 kpc. If they are more like the carbon stars found recently in the Galactic bulge, they may be only half as distant. The surface density of carbon stars as a function of distance is remarkably consistent with an R 1/4 density profile for the Galactic halo. This density profile can be traced to ^ 15 scale radii and fills a volume similar to that occupied by globular clusters. The data yield an effective radius of either 7.0 or 3.5 kpc depending on choice of distance scale. The velocity dispersion of the sample is 96 + 12 km/s. A kinematic model in which vertical velocity dispersion is independent of height above the Galactic plane seems in best accord with the data.
Infrared carbon stars: new identifications and their space distribution in the Galaxy
Astronomy and …, 1998
We present JHKL photometry of a sample of 150 IRAS stars in the third and fourth galactic quadrant with |b| <2 • selected according to their IRAS colour (0.160≤[12-25]≤1.156). We identify 27 carbon star candidates using the [12-25] vs. K-L two-colour diagram method. Among them, 10 are listed in the Stephenson's catalogue of carbon stars and 17 are new infrared carbon stars (IRCS) candidates. Their distances are found to be larger than 3 kpc. These data are combined with previous data to study the space distribution of IRCS. The number density seems to be independent of the galactocentric distance (R) toward the Galactic Center and to decrease exponentially toward the anticenter. At the present stage, it is not possible to disentangle effects such as incompleteness of the sample, different space distribution law and dependence of the luminosity on metallicity. In particular, we suggest that the apparent scarcity of IRCS in the central direction of the Galaxy (R<5 kpc) might be due to a selection effect. From the available data, we have found no IRCS within 1 kpc of the Galactic Center.
NSCC-A NEW SCHEME OF CLASSIFICATION OF C-RICH STARS DEVISED FROM OPTICAL AND INFRARED OBSERVATIONS
Astrophysical Journal, 2009
A new classification system for carbon-rich stars is presented based on an analysis of 51 AGB carbon stars through the most relevant classifying indices available ). The extension incorporated, that also represents the major advantage of this new system, is the combination of the usual optical indices that describe the photospheres of the objects, with new infrared ones, which allow an interpretation of the circumstellar environment of the carbon-rich stars. This new system is presented with the usual spectral subclasses and C 2 -, j-, MS-and temperature indices, and also with the new SiC-(SiC/C.A. abundance estimation) and τ -(opacity) indices. The values for the infrared indices were carried out through a Monte Carlo simulation of the radiative transfer in the circumstellar envelopes of the stars. The full set of indices, when applied to our sample, resulted in a more efficient system of classification, since an examination in a wide spectral range allows us to obtain a complete scenario for carbon stars.
Investigation of faint Galactic carbon stars from the First Byurakan Spectral Sky Survey. II
Astrophysics, 2006
Using recent astronomical databases, we investigate the characteristics of a list of new Galactic carbon (C) stars. These stars were discovered on the First Byurakan Spectral Sky Survey (FBS) plates and constitute the second part of our search for such objects. This second list of FBS C stars contains 44 objects. Slit spectra obtained by us with the BAO 2.6-m telescope confirm the carbon-rich nature of all of them. The list comprises 12 N-type carbon stars and 32 CH-type stars. We consider spectral types, B and R magnitudes retrieved from the USNO-B1.0 catalog, and JHK s near-infrared photometry for stars extracted from the 2MASS point-source catalog. The R magnitudes of our objects are in the range 10 to 14. We derive distance estimates for all objects and find that most of the stars are located between approximately 3 and 20 kpc from the Sun. Their heights above or below the Galactic plane are in the range 1.5 to 13.0 kpc.
The origin of carbon, investigated by spectral analysis of solar-type stars in the Galactic Disk
Arxiv preprint astro-ph/ …, 1998
Abundance analysis of carbon has been performed in a sample of 80 late F and early G type dwarf stars in the metallicity range -1.06 ≤ [Fe/H] ≤ 0.26 using the forbidden [C i] line at 8727 Å. This line is presumably less sensitive to temperature, atmospheric structure and departures from LTE than alternative carbon criteria. We find that [C/Fe] decreases slowly with increasing [Fe/H] with an overall slope of -0.17 ± 0.03. Our results are consistent with carbon enrichment by superwinds of metal-rich massive stars but inconsistent with a main origin of carbon in low-mass stars. This follows in particular from a comparison between the relation of [C/O] with metallicity for the Galactic stars and the corresponding relation observed for dwarf irregular galaxies. The significance of intermediate-mass stars for the production of carbon in the Galaxy is still somewhat unclear.
Preliminary analysis of light curves of the seven carbon stars
2003
We present a preliminary analysis of light curves of the following carbon stars: WZ Cas, VY UMa, Y CVn, RY Dra, T Lyr, HK Lyr and TT Cyg, constructed on the basis of our own BV photoelectric observations done at the Brno Observatory in 1979-94 and Hipparcos observations. The analysis suggests that semiregular light curves of all studied stars can be faithfully expressed by a superposition of long-term changes and a set of medium-term harmonic variations (possibly pulsations) with periods from 50 to 500 days.
The R Coronae Borealis stars: carbon abundances from forbidden carbon lines
Monthly Notices of the Royal Astronomical Society, 2004
Spectra of several R Coronae Borealis (RCB) stars at maximum light have been examined for the [C I] 9850-and 8727-Å absorption lines. The 9850-Å line is variously blended with an Fe II and CN lines, but positive identifications of the [C I] line are made for R CrB and SU Tau. The 8727-Å line is detected in the spectrum of the five stars observed in this wavelength region. Carbon abundances are derived from the [C I] lines using the model atmospheres and atmospheric parameters used by Asplund et al. Although the observed strength of a C I line is constant from cool to hot RCB stars, the strength is lower than predicted by an amount equivalent to a factor of 4 reduction of the gf-value of a line. Asplund et al. dubbed this 'the carbon problem' and discussed possible solutions. The [C I] 9850-Å line seen clearly in R CrB and SU Tau confirms the magnitude of the carbon problem revealed by the C I lines. The [C I] 8727-Å line measured in five stars shows an enhanced carbon problem. The gf-value required to fit the observed [C I] 8727-Å line is a factor of 15 less than the well-determined theoretical gf-value. We suggest that the carbon problem for all lines may be alleviated to some extent by a chromospheric-like temperature rise in these stars. The rise far exceeds that predicted by our non-local thermodynamic equilibrium calculations, and requires a substantial deposition of mechanical energy.
Reprocessing the Hipparcos data for evolved giant stars II. Absolute magnitudes for the R-type carbon stars
Astronomy and Astrophysics, 2001
The Hipparcos Intermediate Astrometric Data for carbon stars have been reprocessed using an algorithm which provides an objective criterion for rejecting anomalous data points and constrains the parallax to be positive. New parallax solutions have been derived for 317 cool carbon stars, mostly of types R and N. In this paper we discuss the results for the 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 red clump giants in the Hertzsprung-Russell diagram. The average absolute magnitude MK for early R-type stars (with V − K < 4) has been derived from a Monte-Carlo simulation implicitly incorporating all possible biases. It appears that the simulated magnitude distribution for a population with a true Gaussian distribution of mean MK = −2.0 and intrinsic standard deviation 1.0 mag provides a satisfactory match to the observed distribution. These values are consistent with the average absolute magnitude MK = −1.6 for clump red giants in the solar neighborhood (Alves 2000). Further, early R-type stars are non-variable, and their infrared photometric properties show that they are not undergoing mass loss, properties similar to those of the red clump giants. Stars with subtypes R4 -R9 tend to be cooler and have similar luminosity to the N-type carbon stars, as confirmed by their position in the (J − H, H − K) color-color diagram. The sample of early R-type stars selected from the Hipparcos Catalogue appears to be approximately complete to magnitude K0 ∼ 7, translating into a 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 that volume, they comprise about 0.04% (0.14% for MK = −1) of the red clump stars in the solar neighborhood. Identification with the red clump locates these stars at the helium core burning stage of stellar evolution, while the N stars are on the asymptotic giant branch, where helium shell burning occurs. The present analysis suggests that for a small fraction of the helium core burning stars (far lower than the fraction of helium shell-burning stars), carbon produced in the interior is mixed to the atmosphere in sufficient quantities to form a carbon star.
Interpretation of carbon overabundances in the atmospheres of carbon stars
Astrophysics and Space Science, 1978
An attempt is made to estimate the rate of accretion of interstellar grains by red giants. It seems possible for a red giant traversing dust clouds to acquire, under realistic conditions, an amount of carbon sufficient to turn its spectrum into that of a carbon star. Coarse grains exceeding 10-3 cm in diameter are most effective in this process.
Near-Infrared Spectra of 29 Carbon Stars: Simple Estimates of Effective Temperature
Publications of the Astronomical Society of Japan, 2007
ABSTRACT
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Faint High-Latitude Carbon Stars Discovered by the Sloan Digital Sky Survey: An Initial Catalog
Astronomical Journal, 2004
A search of more than 3,000 square degrees of high latitude sky by the Sloan Digital Sky Survey has yielded 251 faint high-latitude carbon stars (FHLCs), the large majority previously uncataloged. We present homogeneous spectroscopy, photometry, and astrometry for the sample. The objects lie in the 15.6 < r < 20.8 range, and exhibit a wide variety of apparent photospheric temperatures, ranging from spectral types near M to as early as F. Proper motion measurements for 222 of the objects show that at least 50%, and quite probably more than 60%, of these objects are actually low luminosity dwarf carbon (dC) stars, in agreement with a variety of recent, more limited investigations which show that such objects are the numerically dominant type of star with C_2 in the spectrum. This SDSS homogeneous sample of ~110 dC stars now constitutes 90% of all known carbon dwarfs, and will grow by another factor of 2-3 by the completion of the Survey. As the spectra of the dC and the faint halo giant C stars are very similar (at least at spectral resolution of 1,000) despite a difference of 10 mag in luminosity, it is imperative that simple luminosity discriminants other than proper motion be developed. We use our enlarged sample of FHLCs to examine a variety of possible luminosity criteria, including many previously suggested, and find that, with certain important caveats, JHK photometry may segregate dwarfs and giants.
The APM Survey for cool carbon stars in the Galactic halo -- II. The search for dwarf carbon stars
Monthly Notices of the Royal Astronomical Society, 2000
1 D epartm ent of P hysics, K eel e U niversity,K eel e, Sta ordshire, ST 5 5B G , U K 2 Institute of A stronom y, M adingl ey R oad, C am bridge C B 3 1H A , U K 3 South A frican A stronom icalO bservatory, P .O . B ox 9, 7935 O bservatory, S. A frica D raft version A B ST R A C T W e presentproperm oti on m easurem ents forcarbon starsfound duri ng the A PM Survey forC oolC arbon Starsi n the G al acti c H al o (Totten & Irw i n,1998).M easurem ents are obtai ned usi ng a com bi nati on ofPO SSI,PO SSII and U K ST survey pl ates suppl em ented w here necessary by C C D fram es taken at the Isaac N ew ton Tel escope. W e nd no si gni cant proper m oti on for any ofthe new A PM col our-sel ected carbon stars and so concl ude that there are no dwarfcarbon stars present w i thi n thi s sampl e.W e al so present proper m oti on m easurem ents for three previ ousl y know n dwarf carbon stars and dem onstrate that these m easurem ents agree favourabl y w i th those previ ousl y quoted i n the l i terature,veri fyi ng our m ethod ofdeterm i ni ng proper m oti ons. R esul ts from a com pl i m entary program of JH K photom etry obtai ned at the South A fri can A stronom i calO bservatory are al so presented.D warfcarbon stars are bel i eved to have anom al ous near-i nfrared col ours,and thi s feature i s used for further i nvesti gati on of the nature of the A PM carbon stars. O ur resul ts support the use ofJH K photom tery as a dwarf/gi ant di scri m i nator and al so rei nforce the concl usi on that none ofthe new A PM -sel ected carbon stars are dwarfs.Fi nal l y,proper m oti on m easurem ents com bi ned w i th extant JH K photom etry are presented for a sam pl e of previ ousl y know n H al o carbon stars, suggesti ng that one of these stars, C LS29, i s l i kel y to be a previ ousl y unrecogni sed dwarfcarbon star. K ey w ords: stars:carbon { stars:surveys { astrom etry:stars { i nfrared:stars c 1997 R A S
Faint High-Latitude Carbon Stars Discovered by the Sloan Digital Sky Survey: Methods and Initial Results
We report the discovery of 39 Faint High Latitude Carbon Stars (FHLCs) from Sloan Digital Sky Survey commissioning data. The objects, each selected photometrically and verified spectroscopically, range over 16.6 < r * < 20.0, and show a diversity of temperatures as judged by both colors and NaD line strengths. Although a handful
The Infrared Spectrum of Two Carbon Stars from 4000 to 6700 cm^{-1}
Publications of the Astronomical Society of the Pacific, 1973
The infrared spectra of Y CVn and U Hya from 4000 to 6700 cm -1 are presented. Preliminary identifications of molecular and atomic features have been made. The bearing of these observations on observed C 12 /C 13 ratios is discussed. The spectra are corrected for atmospheric extinction to a reference altitude of 14 km.
Characterisation of Galactic carbon stars and related stars from Gaia EDR3
Astronomy & Astrophysics
The third early Gaia data release (EDR3) has improved the accuracy of the astrometric parameters of numerous long-period variable (LPV) stars. Many of these stars are on the asymptotic giant branch (AGB), showing either a C-rich or O-rich envelope and are characterised by high luminosity, changing surface composition, and intense mass loss. This make them very useful for stellar studies. In a previous investigation, we used Gaia DR2 astrometry to derive the luminosity function, kinematic properties, and stellar population membership of a flux-limited sample of carbon stars in the solar neighbourhood of different spectral types. Here, we extend this initial study to more recent surveys with a greater number of Galactic carbon stars and related stars by adopting the more accurate EDR3 astrometry measurements. Based on a much larger statistics, we confirm that N- and SC-type carbon stars share a very similar luminosity function, while the luminosities of J-type stars (Mbol) are fainter...
Carbon abundances of reference late-type stars from 1D analysis of atomic C i and molecular CH lines
Monthly Notices of the Royal Astronomical Society, 2015
A comprehensive model atom was constructed for C I using the most up-to-date atomic data. We evaluated non-local thermodynamical equilibrium (NLTE) line formation for neutral carbon in classical one-dimensional (1D) models representing atmospheres of late-type stars, where carbon abundance varies from the solar value down to [C/H] = −3. NLTE leads to stronger C I lines compared with their local thermodynamical equilibrium (LTE) strength and negative NLTE abundance corrections, NLTE. The deviations from LTE are large for the strong lines in the infrared (IR), with NLTE = −0.10 to −0.45 dex, depending on stellar parameters, and minor for the weak lines in the visible spectral range, with | NLTE | ≤ 0.03 dex. The NLTE abundance corrections were found to be dependent on the carbon abundance in the model. As the first application of the treated model atom, carbon NLTE abundances were determined for the Sun and eight late-type stars with well-determined stellar parameters that cover the −2.56 ≤ [Fe/H] ≤ −1.02 metallicity range. Consistent abundances from the visible and IR lines were found for the Sun and the most metal-rich star of our sample, when applying a scaling factor of S H = 0.3 to the Drawinian rates of C+H collisions. Carbon abundances were also derived from the molecular CH lines and agree with those from the atomic C I lines for each star. We present the NLTE abundance corrections for lines of C I in the grid of model atmospheres applicable to carbon-enhanced (CEMP) stars.
The Spectroscopic Analysis o f Bright Carbon Stars , Y CVn and U Hya in the One
2006
No. 7] Spectroscopic Analysis in One-Micron Region 535 *' The identification table of them and the description of detailed results in this study will be published elsewhere very soon. No. 7] Spectroscopic Analysis in One-Micron Region 539
Carbon abundances of early B-type stars in the solar vicinity
Astronomy and Astrophysics, 2008
Context. Precise determinations of the chemical composition in early B-type stars constitute fundamental observational constraints on stellar and galactochemical evolution. Carbon, in particular, is one of the most abundant metals in the Universe but analyses in earlytype stars are known to show inconclusive results. Large discrepancies between analyses of different lines in C ii, a failure to establish the C ii/iii ionization balance and the derivation of systematically lower abundances than from other indicators like H ii regions and young FG-type stars pose long-standing problems. Aims. We discuss improvements to the non-LTE modelling of the visual line spectrum and to the spectral analysis of early B-type stars, as well as their consequences for stellar parameter and abundance derivations. The most relevant sources of systematic uncertainies and their effects on the analysis are investigated. Consequences for the present-day carbon abundance in the solar vicinity are discussed. Methods. We present a comprehensive and robust C ii/iii/iv model for non-LTE line-formation calculations based on carefully selected atomic data. The model is calibrated with high-S/N spectra of six apparently slow-rotating early B-type dwarfs and giants, which cover a wide parameter range and are randomly distributed in the solar neighbourhood. A self-consistent quantitative spectrum analysis is performed using an extensive iteration scheme to determine stellar atmospheric parameters and to select the appropriate atomic data used for the derivation of chemical abundances. Results. We establish the carbon ionization balance for all sample stars based on a unique set of input atomic data. Consistency is achieved for all modelled carbon lines of the sample stars. Highly accurate atmospheric parameters and a homogeneous carbon abundance of log (C/H) + 12 = 8.32 ± 0.04 with reduced systematic errors are derived. Present evolution models for massive stars indicate that this value may require only a small adjustment because of the effects of rotational mixing, by < +0.05 dex per sample star. This results in a present-day stellar carbon abundance in the solar neighbourhood, which is in good agreement with recent determinations of the solar value and with the gas-phase abundance of the Orion H ii region. Our finding of a homogeneous presentday carbon abundance also conforms with predictions of chemical-evolution models for the Galaxy. Moreover, the present approach allows us to constrain the effects of systematic errors on fundamental parameters and abundances. This suggests that most of the difficulties found in previous work may be related to large systematic effects in the atmospheric parameter determination and/or inaccuracies in the atomic data.
The Chromospheres of Carbon Stars
Proceedings of the International Astronomical Union
Most oxygen-rich late-type giant stars show evidence for chromospheres in their visual spectra (e.g. Call Η & Κ emission features). Cool (i.e. N-type) non-Mira carbon stars, however, have never been observed to have chromospheric emission in their Call Η & Κ lines. However, faint Mgll h & k lines were detected in emission in low-dispersion IUE spectra of the brightest cool carbon stars in the early 1980s. May 1984 saw the first (and only) successful high-dispersion IUE spectrum taken of a cool carbon star, TX Psc (NO; C6,2). Armed with this high-dispersion spectrum, as well as low-dispersion IUE and ground-based spectra, Luttermoser et al. (1989) made the first detailed attempt to semiempirically model the chromosphere of a cool carbon star. This model was successful in reproducing the Mgll lines, but it was not well constrained due to the lack of other observed high-resolution chromospheric profiles for comparison. Modeling carbon star chromospheres can now be addressed more accurately with HST/GHRS high-resolution spectra. New fluoresced emission features have been discovered in the GHRS spectra of carbon stars that are not present in their oxygen-rich counterparts.
Infrared observations of peculiar carbon stars
1997
We present a uniform and high quality set of infrared photometric (JHK) observations of the 6 peculiar carbon giant stars V Ari, UV Cam, BD+34 911, TU Gem, BD+57 2161 and BD+34 4134. All of these belong to the small group of known cool CH giants populating the Galactic halo. Comparison of the J − H and H − K colours to "normal" C stars show our stars to be "bluer" (i.e., having lower values of J − H and H − K) than the bulk of the Galactic C stars. Comparison with synthetic JHK colours reveal 5 of our 6 stars as having considerably lower metallicities and/or higher temperatures than the bulk. Using standard assumptions we derive estimates of their effective temperatures, gravities, luminosities and distances. Their derived luminosities place them close to (or below) the theoretical first He shell flash luminosity, although other observations indicate their carbon excess to be intrinsic.
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