Садржај
Слике
Уплоадјуј своје слике
DSS Images Other Images
Везани чланци
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
| Re-processing the Hipparcos Transit Data and Intermediate Astrometric Data of spectroscopic binaries. I. Ba, CH and Tc-poor S stars
Only 235 entries were processed as astrometric binaries with orbits inthe Hipparcos and Tycho Catalogue (\cite{Hipparcos}). However, theIntermediate Astrometric Data (IAD) and Transit Data (TD) made availableby ESA make it possible to re-process the stars that turned out to bespectroscopic binaries after the completion of the Catalogue. This paperillustrates how TD and IAD may be used in conjunction with the orbitalparameters of spectroscopic binaries to derive astrometric parameters.The five astrometric and four orbital parameters (not already known fromthe spectroscopic orbit) are derived by minimizing an objective function(chi 2) with an algorithm of global optimization. This codehas been applied to 81 systems for which spectroscopic orbits becameavailable recently and that belong to various families ofchemically-peculiar red giants (namely, dwarf barium stars, strong andmild barium stars, CH stars, and Tc-poor S stars). Among these 81systems, 23 yield reliable astrometric orbits. These 23 systems make itpossible to evaluate on real data the so-called ``cosmic error''described by Wielen et al. (1997), namely the fact that an unrecognizedorbital motion introduces a systematic error on the proper motion.Comparison of the proper motion from the Hipparcos catalogue with thatre-derived in the present work indicates that the former are indeed faroff the present value for binaries with periods in the range 3 to ~ 8years. Hipparcos parallaxes of unrecognized spectroscopic binaries turnout to be reliable, except for systems with periods close to 1 year, asexpected. Finally, we show that, even when a complete orbital revolutionwas observed by Hipparcos, the inclination is unfortunately seldomprecise. Based on observations from the Hipparcos astrometric satelliteoperated by the European Space Agency (ESA 1997).
| Insights into the formation of barium and Tc-poor S stars from an extended sample of orbital elements
The set of orbital elements available for chemically-peculiar red giant(PRG) stars has been considerably enlarged thanks to a decade-longCORAVEL radial-velocity monitoring of about 70 barium stars and 50 Sstars. When account is made for the detection biases, the observedbinary frequency among strong barium stars, mild barium stars andTc-poor S stars (respectively 35/37, 34/40 and 24/28) is compatible withthe hypothesis that they are all members of binary systems. Thesimilarity between the orbital-period, eccentricity and mass-functiondistributions of Tc-poor S stars and barium stars confirms that Tc-poorS stars are the cooler analogs of barium stars. A comparative analysisof the orbital elements of the various families of PRG stars, and of asample of chemically-normal, binary giants in open clusters, revealsseveral interesting features. The eccentricity - period diagram of PRGstars clearly bears the signature of dissipative processes associatedwith mass transfer, since the maximum eccentricity observed at a givenorbital period is much smaller than in the comparison sample of normalgiants. be held The mass function distribution is compatible with theunseen companion being a white dwarf (WD). This lends support to thescenario of formation of the PRG star by accretion of heavy-element-richmatter transferred from the former asymptotic giant branch progenitor ofthe current WD. Assuming that the WD companion has a mass in the range0.60+/-0.04 Msb ȯ, the masses of mild and strong barium starsamount to 1.9+/-0.2 and 1.5+/-0.2 Msb ȯ, respectively. Mild bariumstars are not restricted to long-period systems, contrarily to what isexpected if the smaller accretion efficiency in wider systems were thedominant factor controlling the pollution level of the PRG star. Theseresults suggest that the difference between mild and strong barium starsis mainly one of galactic population rather than of orbital separation,in agreement with their respective kinematical properties. There areindications that metallicity may be the parameter blurring the period -Ba-anomaly correlation: at a given orbital period, increasing levels ofheavy-element overabundances are found in mild barium stars, strongbarium stars, and Pop.II CH stars, corresponding to a sequence ofincreasingly older, i.e., more metal-deficient, populations. PRG starsthus seem to be produced more efficiently in low-metallicitypopulations. Conversely, normal giants in barium-like binary systems mayexist in more metal-rich populations. HD 160538 (DR Dra) may be such anexample, and its very existence indicates at least that binarity is nota sufficient condition to produce a PRG star. This paper is dedicated tothe memory of Antoine Duquennoy, who contributed many among theobservations used in this study
| Barium stars, galactic populations and evolution.
In this paper HIPPARCOS astrometric and kinematical data together withradial velocities from other sources are used to calibrate bothluminosity and kinematics parameters of Ba stars and to classify them.We confirm the results of our previous paper (where we used data fromthe HIPPARCOS Input Catalogue), and show that Ba stars are aninhomogeneous group. Five distinct classes have been found i.e. somehalo stars and four groups belonging to disk population: roughlysuper-giants, two groups of giants (one on the giant branch, the otherat the clump location) and dwarfs, with a few subgiants mixed with them.The confirmed or suspected duplicity, the variability and the range ofknown orbital periods found in each group give coherent resultssupporting the scenario for Ba stars that are not too highly massivebinary stars in any evolutionary stages but that all were previouslyenriched with Ba from a more evolved companion. The presence in thesample of a certain number of ``false'' Ba stars is confirmed. Theestimates of age and mass are compatible with models for stars with astrong Ba anomaly. The mild Ba stars with an estimated mass higher than3Msun_ may be either stars Ba enriched by themselves or``true'' Ba stars, which imposes new constraints on models.
| Absolute magnitudes and kinematics of barium stars.
The absolute magnitude of barium stars has been obtained fromkinematical data using a new algorithm based on the maximum-likelihoodprinciple. The method allows to separate a sample into groupscharacterized by different mean absolute magnitudes, kinematics andz-scale heights. It also takes into account, simultaneously, thecensorship in the sample and the errors on the observables. The methodhas been applied to a sample of 318 barium stars. Four groups have beendetected. Three of them show a kinematical behaviour corresponding todisk population stars. The fourth group contains stars with halokinematics. The luminosities of the disk population groups spread alarge range. The intrinsically brightest one (M_v_=-1.5mag,σ_M_=0.5mag) seems to be an inhomogeneous group containing bariumbinaries as well as AGB single stars. The most numerous group (about 150stars) has a mean absolute magnitude corresponding to stars in the redgiant branch (M_v_=0.9mag, σ_M_=0.8mag). The third group containsbarium dwarfs, the obtained mean absolute magnitude is characteristic ofstars on the main sequence or on the subgiant branch (M_v_=3.3mag,σ_M_=0.5mag). The obtained mean luminosities as well as thekinematical results are compatible with an evolutionary link betweenbarium dwarfs and classical barium giants. The highly luminous group isnot linked with these last two groups. More high-resolutionspectroscopic data will be necessary in order to better discriminatebetween barium and non-barium stars.
| 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.
| UBV photometry of barium stars
Magnitudes in V and B-V and U-B colors observed by the 91-cm telescopeat Okayama are presented for 109 stars including both classical andmarginal barium stars. The two-color diagram shows a fair amount ofspread. This can be interpreted by interstellar reddening and variableamounts of line blocking effect. Both classical and marginal bariumstars form a fairly homogeneous group.
| Taxonomy of barium stars
Spectral classification, barium intensity, radial velocity, luminosity,and kinematical properties are determined for 389 barium stars byanalyzing image-tube spectra and photometric observation data. Diskkinematics for the stars are based on whether they are Ba weak or Bastrong. Weak barium stars in general have smaller velocity dispersions,brighter apparent magnitude, and lower luminosity than strong bariumstars. These characteristics are confirmed by solving for meanspectroscopic distances, z-scale height distances, and reduced propermotions.
| The binary nature of the barium and CH stars. III - Orbital parameters
Results are presented from a 10-year program to monitor the velocityvariations of Ba II and CH stars, showing that all Ba II and CH starsare binaries. Radial-velocity observations for Ba II and CH binaries aregiven. Also, the results of orbit calculations and orbital elementdeterminations are analyzed. It is shown that the eccentricities of BaII star orbits are significantly lower than the eccentricities for asample of normal G and K giants. In addition, the eccentricities of CHstar orbits are significantly lower than those of Ba II stars,suggesting dissipation due to mass exchange, probably from a previousAGB star. The mass functions for Ba II and CH stars indicate that thestars come from samples of binary systems with a small dispersion inmass ratios. If the Ba II and CH stars are assumed to have masses of 1.5and 0.8 solar mass, respectively, then their companions would havemasses near 0.6 solar mass, similar to the values expected for whitedwarfs.
| Kinematic and spatial distributions of barium stars - Are the barium stars and AM stars related?
The possibility of an evolutionary link between Am stars and bariumstars is considered, and an examination of previous data suggests thatbarium star precursors are main-sequence stars of intermediate mass, aremost likely A and/or F dwarfs, and are intermediate-mass binaries withclose to intermediate orbital separations. The possible role of masstransfer in the later development of Am systems is explored. Masstransfer and loss from systems with a range of masses and orbitalseparations may explain such statistical peculiarities of barium starsas the large dispersion in absolute magnitude, the large range ofelemental abundances from star to star, and the small number of starswith large peculiar velocities.
| Spectroscopic binaries - 15th complementary catalog
Published observational data on the orbital characteristics of 436spectroscopic binaries, covering the period 1982-1986, are compiled intables. The data sources and the organization of the catalog are brieflydiscussed, and notes are provided for each item.
| Notre article de synthèse: Les étoiles à Baryum expliquées?
Not Available
| Additional late-type stars with technetium
The results of a survey of 279 late-type giants and supergiants for thespectral lines of the radioactive element technetium (Tc I) at 4297,4262, and 4238 A are presented. The following conclusions are reached:(1) the presence of Tc correlates very strongly with the existence oflight variability; (2) evolutionary MS stars show Tc and spectroscopicMS stars do not show Tc; (3) single S stars show Tc; (4) SC stars showTc; (5) about 75 percent of the C stars show Tc; and (6) Ba II stars donot show Tc. The findings are compatible with predictions from stellarevolution theory.
| Photoelectric photometry of carbon and barium stars in the Vilnius seven-color system and their color excesses
Not Available
| E. W. Fick Observatory stellar radial velocity measurements. I - 1976-1984
Stellar radial velocity observations made with the large vacuumhigh-dispersion photoelectric radial velocity spectrometer at FickObservatory are reported. This includes nearly 2000 late-type starsobserved during 585 nights. Gradual modifications to this instrumentover its first eight years of operation have reduced the observationalerror for high-quality dip observations to + or - 0.8 km/s.
| Luminosity classification with the Washington system
The DDO 51 filter has been added to the Washington photometric system.The strong surface gravity sensitivity of the Mg I 'b' triplet and MgHbands which it monitors allows the system to easily discriminate betweendwarfs and giants of late G and K spectral type. The system isespecially suited as a membership criterion for abundance studies ofdistant cluster giants. The Mg index is insensitive to surface gravityvariations among G giants. The metallicity sensitivity among giants isalso relatively weak. Population I and II giants can be distinguishedbut no further differentiation is evident.
| Lithium in the barium stars
New high-resolution spectra of the lithium resonance doublet haveprovided lithium abundances or upper limits for 26 classical and mildbarium stars. The lithium lines always are present in the classicalbarium stars. Lithium abundances in these stars obey a trend withstellar masses consistent with that previously derived for ordinary Kgiants. This supports the notion that classical barium stars arepost-core-He-flash or core-He-burning stars. Lithium contents in themild barium stars, however, often are much smaller than those of theclassical barium stars; sometimes only upper limits may be determined.The cause for this difference is not easily understood, but may berelated to more extensive mass loss by the mild barium stars.
| A search for light variations in barium stars
Seventeen barium stars have been investigated for possible lightvariations. Ten of these stars have been monitored for twelve years.
| A catalog of spectral classification and photometry of barium stars
Many other Ba II stars have been found, since the enhancement of theline of singly ionized barium (4554 A) in late-type, high-luminositystars was discovered by Bidelman and Keenan (1951). The majority ofstars so identified are listed in a study conducted by MacConnell et al.(1972). MacConnell et al. identified 150 'certain' barium stars and anadditional 90 'marginal' barium stars from inspection of objective-prismplates of the Michigan Spectral Survey of the southern sky. Since themajority of known Ba II stars were discovered with objective-prismplates, they have lacked high-quality spectral classifications. It hasbeen attempted to obtain these data along with broad- andintermediate-band photometry, in order to study the properties of thissubgroup of stars in greater detail than has heretofore been possible.Except for the stars recently identified by Bidelman (1981), the list ofspectroscopic and photometric data in Table 1 includes virtually allrecognized barium stars. The stars identified by Bidelman are listed inTable 2.
| The binary nature of the barium stars. II - Velocities, binary frequency, and preliminary orbits
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1983ApJ...268..264M&db_key=AST
| The Washington system - Photometric properties and standard stars
Observations on the Washington Photometric System (C,M,T1,T2), leadingto an expanded set of 79 standards, are presented. This primary standardlist extends to a V magnitude of approximately 12.0. A V filter has beenadded to the system, which permits V-T1 colors and V magnitudes on theJohnson system. Revised primary and secondary extinction values fromfour observatories are presented. The extent of errors in the standardcolors is discussed. Reddening effects are also discussed.
| Technetium in late-type stars. I - Observations
An analysis of about 90 spectra (11 or 13 A/mm) of nonvariable andvariable (mostly Mira variables) M, MS, S, CS, and C stars for thepresence of the radioactive element technetium (half-life of about200,000 y) suggests that Tc is most often present at certain variabilityperiods. Stars with no Tc I lines in their spectra can be found at mostperiods (mean period, 234 d), whereas stars with Tc I lines have periodsin most cases in excess of 300 days (mean period, 330 d + or - 83 d).Interpreting the data in terms of kinematic studies by Feast (1963)suggests that the stars with Tc are Pop I and that variables without Tcare largely Pop II type stars.
| 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.
| Broad-band photometry of G and K stars - The C, M, T/1/, T/2/ photometric system
An alternative broad-band photometric system is described which isdesigned to obtain accurate photometric temperatures, metal abundances,and a cyanogen blanketing index for G and K giants. The filters definingthe system are given along with the effective wavelength of eachbandpass, the bandpass width for one-half maximum responsivity, and theresponse function of the system. A comparison with the UBV broad-bandsystem shows that the C, M, T(1), T(2) system is more efficient since itrequires less observing time to obtain all three parameters than the UBVsystem needs just for two of them. The reduction of observations isoutlined, and the definition of the standard system is described indetail. Results are presented for abundance analyses of 36 G and Kgiants; 23 members of the Hyades, Praesepe, and M67; 7 super-metal-richstars; and also 26 G-type dwarfs. Effects of reddening and luminosity onthe metallicity and CN indices are examined.
| A comment on the spectral energy distributions of Ba II stars.
Abstract image available at:http://adsabs.harvard.edu/abs/1975MNRAS.173P..83F
| Absolute magnitudes of barium stars based on the width of H alpha in absorption.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1975PASP...87..537K&db_key=AST
| The absolute magnitudes of the barium stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972AJ.....77..384M&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 barium stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1965MNRAS.129..263W&db_key=AST
| A Search for BA II Stars
Not Available
|
Додај нови чланак
Линкови у сродству са темом
Додај нови линк
Чланови следећих група \:
|
Посматрања и Астрометриски подаци
| Сазвежђа: | Кочијаш |
| Ректацензија: | 04h59m03.73s |
| Deклинација: | +51°56'32.1" |
| Apparent магнитуда: | 8.116 |
| Даљина: | 220.264 parsecs |
| Proper motion RA: | -6.1 |
| Proper motion Dec: | -3.3 |
| B-T magnitude: | 9.839 |
| V-T magnitude: | 8.259 |
Каталог и designations:
|
