Contenuti
Immagini
Carica la tua immagine
DSS Images Other Images
Articoli relazionati
The Geneva-Copenhagen survey of the solar neighbourhood. III. Improved distances, ages, and kinematics
Context: Ages, chemical compositions, velocity vectors, and Galacticorbits for stars in the solar neighbourhood are fundamental test datafor models of Galactic evolution. The Geneva-Copenhagen Survey of theSolar Neighbourhood (Nordström et al. 2004; GCS), amagnitude-complete, kinematically unbiased sample of 16 682 nearby F andG dwarfs, is the largest available sample with complete data for starswith ages spanning that of the disk. Aims: We aim to improve theaccuracy of the GCS data by implementing the recent revision of theHipparcos parallaxes. Methods: The new parallaxes yield improvedastrometric distances for 12 506 stars in the GCS. We also use theparallaxes to verify the distance calibration for uvby? photometryby Holmberg et al. (2007, A&A, 475, 519; GCS II). We add newselection criteria to exclude evolved cool stars giving unreliableresults and derive distances for 3580 stars with large parallax errorsor not observed by Hipparcos. We also check the GCS II scales of T_effand [Fe/H] and find no need for change. Results: Introducing thenew distances, we recompute MV for 16 086 stars, and U, V, W,and Galactic orbital parameters for the 13 520 stars that also haveradial-velocity measurements. We also recompute stellar ages from thePadova stellar evolution models used in GCS I-II, using the new valuesof M_V, and compare them with ages from the Yale-Yonsei andVictoria-Regina models. Finally, we compare the observed age-velocityrelation in W with three simulated disk heating scenarios to show thepotential of the data. Conclusions: With these revisions, thebasic data for the GCS stars should now be as reliable as is possiblewith existing techniques. Further improvement must await consolidationof the T_eff scale from angular diameters and fluxes, and the Gaiatrigonometric parallaxes. We discuss the conditions for improvingcomputed stellar ages from new input data, and for distinguishingdifferent disk heating scenarios from data sets of the size andprecision of the GCS.Full Table 1 is 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/501/941
| 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.
| CNO Abundances of Hydrogen-Deficient Carbon and R Coronae Borealis Stars: A View of the Nucleosynthesis in a White Dwarf Merger
We present high-resolution (R ~ 50, 000) observations of near-IRtransitions of CO and CN of the five known hydrogen-deficient carbon(HdC) stars and four R Coronae Borealis (RCB) stars. We perform anabundance analysis of these stars by using spectrum synthesis andstate-of-the-art MARCS model atmospheres for cool hydrogen-deficientstars. Our analysis confirms reports by Clayton and colleagues thatthose HdC stars exhibiting CO lines in their spectrum and the cool RCBstar S Aps are strongly enriched in 18O (with16O/18O ratios ranging from 0.3 to 16). Nitrogenand carbon are in the form of 14N and 12C,respectively. Elemental abundances for CNO are obtained from C I,C2, CN, and CO lines. Difficulties in deriving the carbonabundance are discussed. Abundances of Na from Na I lines and Sfrom S I lines are obtained. Elemental and isotopic CNO abundancessuggest that HdC and RCB stars may be related objects, and that theyprobably formed from a merger of an He white dwarf with a C-O whitedwarf.
| Fluorine in R Coronae Borealis Stars
Neutral fluorine (F I) lines are identified in the optical spectra ofseveral R Coronae Borealis stars (RCBs) at maximum light. These linesprovide the first measurement of the fluorine abundance in these stars.Fluorine is enriched in some RCBs by factors of 800-8000 relative to itslikely initial abundance. The overabundances of fluorine are evidencefor the synthesis of fluorine. These results are discussed in the lightof the scenario that RCBs are formed by accretion of an He white dwarfby a CO white dwarf. Sakurai's object (V4334 Sgr), a final He-shellflash product, shows no detectable F I lines.
| Galactic distributions and statistics of the HD stars in the michigan spectral catalogue.
Not Available
| An evolutionary catalogue of galactic post-AGB and related objects
Aims.With the ongoing AKARI infrared sky survey, of much greatersensitivity than IRAS, a wealth of post-AGB objects may be discovered.It is thus time to organize our present knowledge of known post-AGBstars in the galaxy with a view to using it to search for new post-AGBobjects among AKARI sources. Methods: We searched the literatureavailable on the NASA Astrophysics Data System up to 1 October 2006, anddefined criteria for classifying sources into three categories: verylikely, possible and disqualified post-AGB objects. The category of verylikely post-AGB objects is made up of several classes. Results: We havecreated an evolutionary, on-line catalogue of Galactic post-AGB objects,to be referred to as the Toruń catalogue of Galactic post-AGB andrelated objects. The present version of the catalogue contains 326 verylikely, 107 possible and 64 disqualified objects. For the very likelypost-AGB objects, the catalogue gives the available optical and infraredphotometry, infrared spectroscopy and spectral types, and links tofinding charts and bibliography.A stable version of the catalogue is available 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/469/799
| Very Large Excesses of 18O in Hydrogen-deficient Carbon and R Coronae Borealis Stars: Evidence for White Dwarf Mergers
We have found that at least seven hydrogen-deficient carbon (HdC) and RCoronae Borealis (RCB) stars, have 16O/18O ratiosclose to and in some cases less than unity, values that are orders ofmagnitude lower than measured in other stars (the solar value is 500).Greatly enhanced 18O is evident in every HdC and RCB we havemeasured that is cool enough to have detectable CO bands. The three HdCstars measured have 16O/18O<1, lower valuesthan any of the RCB stars. These discoveries are important clues indetermining the evolutionary pathways of HdC and RCB stars, for whichtwo models have been proposed: the double degenerate (white dwarf [WD]merger) and the final helium-shell flash (FF). No overproduction of18O is expected in the FF scenario. We have quantitativelyexplored the idea that HdC and RCB stars originate in the mergers of CO-and He-WDs. The merger process is estimated to take only a few days,with accretion rates of 150 Msolar yr-1 producingtemperatures at the base of the accreted envelope of(1.2-1.9)×108 K. Analysis of a simplified one-zonecalculation shows that nucleosynthesis in the dynamically accretingmaterial may provide a suitable environment for a significant productionof 18O, leading to very low values of16O/18O, similar to those observed. We also findqualitative agreement with observed values of 12C/13C and with the CNO elemental ratios. H-admixture during theaccretion process from the small H-rich C/O WD envelope may play animportant role in producing the observed abundances. Overall, ouranalysis shows that WD mergers may very well be the progenitors ofO18-rich RCB and HdC stars, and that more detailedsimulations and modeling are justified.
| An Extremely Large Excess of 18O in the Hydrogen-deficient Carbon Star HD 137613
We report the discovery of a uniquely large excess of 18O inthe hydrogen-deficient carbon (HdC) star HD 137613 based on a spectrumof the first-overtone bands of CO at 2.3-2.4 μm in which three strongabsorption bands of 12C18O are clearly present.Bands of 12C16O also are present, but no bands of13C16O or 12C17O are seen.We estimate an isotopic ratio 16O/18O <~ 1. Thesolar value of this ratio is ~500. Neither He-core burning nor He-shellflash burning can produce the isotopic ratios of oxygen and carbonobserved in HD 137613. However, a remarkable similarity exists betweenthe observed abundances and those found in the outer layers of the broadHe shell of early-asymptotic giant branch (AGB) stars, soon after theend of He-core burning. It is not known how the outer envelope down tothe He shell could be lost, but some mechanism of enhanced mass lossmust be involved. HD 137613 may be a post-early-AGB star with the outerlayers of the former He-burning shell as its photosphere. The unusualelemental abundances of the HdC stars resemble those of the R CoronaeBorealis (RCB) stars, but HdC stars do not produce clouds of dust thatproduce declines in brightness. None of the other RCB or HdC starsobserved show significant 18O.
| The Hydrogen-Deficient Carbon Star XX Cam
The high resolution and high S/N spectra of a nonvariablehydrogen-deficient carbon star XX Cam were analyzed and the chemicalcomposition derived. The atmospheric parameters of XX Cam areTeff=7250 K, log g= 0.8 and mean ξt=5 kms-1. The microturbulent velocity is variable with depth inthe star's atmosphere. The extreme hydrogen deficiency of XX Cam isconfirmed. No lithium is found. The abundances of other light elementsare close to the abundances in the majority group of R CrB stars. Theabundances of s-process elements are not enhanced.
| The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of 14 000 F and G dwarfs
We present and discuss new determinations of metallicity, rotation, age,kinematics, and Galactic orbits for a complete, magnitude-limited, andkinematically unbiased sample of 16 682 nearby F and G dwarf stars. Our63 000 new, accurate radial-velocity observations for nearly 13 500stars allow identification of most of the binary stars in the sampleand, together with published uvbyβ photometry, Hipparcosparallaxes, Tycho-2 proper motions, and a few earlier radial velocities,complete the kinematic information for 14 139 stars. These high-qualityvelocity data are supplemented by effective temperatures andmetallicities newly derived from recent and/or revised calibrations. Theremaining stars either lack Hipparcos data or have fast rotation. Amajor effort has been devoted to the determination of new isochrone agesfor all stars for which this is possible. Particular attention has beengiven to a realistic treatment of statistical biases and errorestimates, as standard techniques tend to underestimate these effectsand introduce spurious features in the age distributions. Our ages agreewell with those by Edvardsson et al. (\cite{edv93}), despite severalastrophysical and computational improvements since then. We demonstrate,however, how strong observational and theoretical biases cause thedistribution of the observed ages to be very different from that of thetrue age distribution of the sample. Among the many basic relations ofthe Galactic disk that can be reinvestigated from the data presentedhere, we revisit the metallicity distribution of the G dwarfs and theage-metallicity, age-velocity, and metallicity-velocity relations of theSolar neighbourhood. Our first results confirm the lack of metal-poor Gdwarfs relative to closed-box model predictions (the ``G dwarfproblem''), the existence of radial metallicity gradients in the disk,the small change in mean metallicity of the thin disk since itsformation and the substantial scatter in metallicity at all ages, andthe continuing kinematic heating of the thin disk with an efficiencyconsistent with that expected for a combination of spiral arms and giantmolecular clouds. Distinct features in the distribution of the Vcomponent of the space motion are extended in age and metallicity,corresponding to the effects of stochastic spiral waves rather thanclassical moving groups, and may complicate the identification ofthick-disk stars from kinematic criteria. More advanced analyses of thisrich material will require careful simulations of the selection criteriafor the sample and the distribution of observational errors.Based on observations made with the Danish 1.5-m telescope at ESO, LaSilla, Chile, and with the Swiss 1-m telescope at Observatoire deHaute-Provence, France.Complete Tables 1 and 2 are 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/418/989
| 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
| Hydrogen-Deficient Cargon Star HM Lib
The high and medium resolution spectra of a nonvariablehydrogen-deficient carbon star (HdC) HM Lib were analyzed and thechemical composition derived. The atmospheric parameters of HM Lib areTeff = 6000+/-200 K, log g = 1.3+/-0.5 and the microturbulentvelocity xi_t = 6.8+/-1.0 km/s. The high hydrogen deficiency isconfirmed. The abundances of other elements are close to those found forthe majority of warmer and variable R CrB stars. The medium resolutionspectrum of another HdC star HD 182040 is compared to that of HM Lib. Inthe spectrum of HD 182040 the CN red system bands are weaker due to 0.3dex lower N abundance.
| 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.
| HIPPARCOS observations of hydrogen-deficient carbon stars
Parallax measurements for 21 hydrogen-deficient carbon stars have beenmade by the Hipparcos satellite. These stars include most of thebrighter R Coronae Borealis (RCB) variables, other coolhydrogen-deficient carbon (HdC) stars, and several higher-temperatureextreme helium (eHe) stars. Most of these stars have either negative orstatistically insignificant parallaxes, indicating that they lie beyondthe detection capability of Hipparcos. Although the distances to thegalactic hydrogen-deficient carbon stars remain unknown, at least theHipparcos observations do confirm that these objects must have highluminosity like the LMC RCB stars, for which M_bol = -4 to -5. Basedupon Hipparcos proper motions, we derive UVW velocities for the RCB andHdC stars, assuming M_bol = -3 and -5. The UW-velocity dispersion of theRCB/HdC stars is similar to that already reported for the eHe stars,further supporting that these groups of stars have predominantly bulgedistributions. However, UW Cen may be a second example of a halo RCBstar currently seen transitting the galactic plane.
| A catalogue of [Fe/H] determinations: 1996 edition
A fifth Edition of the Catalogue of [Fe/H] determinations is presentedherewith. It contains 5946 determinations for 3247 stars, including 751stars in 84 associations, clusters or galaxies. The literature iscomplete up to December 1995. The 700 bibliographical referencescorrespond to [Fe/H] determinations obtained from high resolutionspectroscopic observations and detailed analyses, most of them carriedout with the help of model-atmospheres. The Catalogue is made up ofthree formatted files: File 1: field stars, File 2: stars in galacticassociations and clusters, and stars in SMC, LMC, M33, File 3: numberedlist of bibliographical references The three files are only available inelectronic form at the Centre de Donnees Stellaires in Strasbourg, viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5), or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| The R Coronae Borealis stars - I. Infrared photometry and long-term variations
Extensive JHKL photometry is given for 12 R Coronae Borealis (RCB)stars, covering periods of up to 23 years. Limited infrared observationsof a few other RCB stars and five HdC stars are also reported. Thesedata are used to study the long-term variations of the stars (at J) andof the circumstellar dust (at L). All of the RCB stars show variationsin the flux from the dust on time-scales of from a few hundred days to afew thousand days. Dust flux amplitudes at L of up to 3mag are found,the larger amplitudes being associated with the longer time-scales.Secular variations over about 10000d are also sometimes seen. R CrBitself is atypical in showing evidence of semiregular variations (period~1260d). There is no direct relation between the occurrence ofobscuration minima and changes in the flux from the dust. However, thereis possibly a statistical relation between the dust flux and thefrequency of the obscuration minima. Models involving fixed geometry forthe ejection of dust from the star appear to be ruled out and the datasupport the random dust-puff model. High infrared excesses and highlevels of obscuration activity seem to be associated with a higher thanaverage hydrogen abundance.
| The radial velocity variations of cool hydrogen-deficient carbon stars
We have obtained a series of radial velocities for many of the brightgalactic R Coronae Borealis (RCB) and hydrogen-deficient carbon (HdC)stars, in order to characterize the pulsations of these types of coolhydrogen-deficient carbon stars. By comparing these velocities with theresults of long-term photometric monitoring, we investigate thepulsation properties of these objects, the link between pulsations andmass loss, and the relationship between these stars and the higher-T_effhydrogen-deficient stars, the extreme helium (eHe) stars. We find thatmost of the RCB stars have radial velocity and V light amplitudes of10-20kms^-1 and 0.2-0.3 mag, respectively. Pulsationally more-activestars such as RY Sgr are rare. Only one other RCB star, RT Nor, has asimilar photometric amplitude to RY Sgr, but this star has a much lowerradial velocity amplitude. With only one exception, HD 175893, all ofthe HdC stars have a lower pulsation amplitude than the RCB stars. Sincethe RCB and HdC stars appear to be distinguished by the large-amplitudedeclines and infrared excesses of the RCB stars, we suggest that thepulsation amplitude dictates whether significant mass loss occurs inthese objects. The radial velocity-to-light amplitude (RV/V) ratioappears to be temperature dependent, but we suspect that this is not anintrinsic effect. The 7000-K group of RCB stars haveRV/V~50kms^-1mag^-1, which is similar to radially pulsating Cepheids.The similar pulsation properties of the RCB and HdC stars and the coolereHe stars provide further evidence that these types of stars are closelyrelated.
| V854 Centauri - the first 3000 days.
Not Available
| 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
| A large, complete, volume-limited sample of G-type dwarfs. I. Completion of Stroemgren UVBY photometry
Four-colour photometry of potential dwarf stars of types G0 to K2,selected from the Michigan Spectral Catalogues (Vol. 1-3), has beencarried out. The results are presented in a catalogue containing 4247uvby observations of 3900 stars, all south of δ = -26deg. Theoverall internal rms errors of one observation (transformed to thestandard system) of a program star in the interval 8.5 < V < 10.5are 0.0044, 0.0021, 0.0039, and 0.0059, respectively, in V, b-y, m_1_ ,and c_1_. The purpose of the catalogue, combined with earliercatalogues, is to allow selection of a large, complete, volume-limitedsample of G- and K-type dwarfs, investigate their metallicitydistribution, and compare it to predictions of various models ofgalactic chemical evolution. Future papers in this series will discussthese subjects.
| Revised MK spectral classification of the red carbon stars
The spectral classification of the red carbon stars has been broughtinto the revised MK system by combining some of the features of the oldR, N, and C classifications, as modified by Yamashita, and addingnumerical abundance indices. The new types are intended to (1) definethe population to which the star belongs, (2) allow quick interpolationbetween the detailed atmospheric analyses of individual stars, and (3)indicate the differences between carbon stars in different parts of ourgalaxy, and in other galaxies. It is the flexibility of the notation,allowing the incorporation of improved criteria, that should make thenew system useful.
| A catalogue of Fe/H determinations - 1991 edition
A revised version of the catalog of Fe/H determinations published by G.Cayrel et al. (1985) is presented. The catalog contains 3252 Fe/Hdeterminations for 1676 stars. The literature is complete up to December1990. The catalog includes only Fe/H determinations obtained from highresolution spectroscopic observations based on detailed spectroscopicanalyses, most of them carried out with model atmospheres. The catalogcontains a good number of Fe/H determinations for stars from open andglobular clusters and for some supergiants in the Magellanic Clouds.
| The Photometric Characteristics of Cool Hydrogen Deficient Carbon Stars
Abstract image available at:http://adsabs.harvard.edu/abs/1990MNRAS.247...91L
| The 70th Name-List of Variable Stars
Not Available
| Photometry of R Coronae Borealis and hydrogen-deficient carbon stars, II 1986.
Not Available
| A general catalogue of cool carbon stars
Not Available
| Discovery of variability in the 'non-variable' hydrogen-deficient carbon stars
The supposedly nonvariable hydrogen-deficient carbon stars HD 137613,148839, 173409, 175893, and 182040 have been shown to be variable fromphotoelectric UBV and RI(KC) photometry during 1982-83 and 1986. HD175893 is found to have a range in V of at least 0.25 mag and magnitudeand color variations which are typical of RCB stars at maximum light.The other four stars show V, (B-V), and (U-B) variations of up to 0.07mag. All of the stars studied are shown to be small amplitude variableswith the possible exception of HD 173409.
| UBVRI observations of stars in the fields of five open clusters with nearby carbon stars
UBVRI photoelectric observations of stars in the fields of five openclusters with carbon stars in or very near the cluster area arereported. In three cases it is found that the carbon stars, treated asmembers of the clusters, receive absolute visual and bolometricmagnitudes within the range normally accepted for this class. In thecase of the other two clusters, the carbon stars are found to benonmembers, and at greater distances.
|
Sottometti un nuovo articolo
Link relazionati
Sottometti un nuovo link
Membro dei seguenti gruppi:
|
Osservazione e dati astrometrici
| Costellazione: | Triangolo Australe |
| Ascensione retta: | 16h35m45.78s |
| Declinazione: | -67°07'36.7" |
| Magnitudine apparente: | 8.268 |
| Distanza: | 680.272 parsec |
| Moto proprio RA: | -7.2 |
| Moto proprio Dec: | -3.7 |
| B-T magnitude: | 9.44 |
| V-T magnitude: | 8.365 |
Cataloghi e designazioni:
|
