目录
图像
上传图像
DSS Images Other Images
相关文章
BVRI Photometry of nz Gem, HD 73017, HD 77247, RT Vir and 104 Her
We examined single channel differential BVRI photometry of the coolstars NZ Gem, HD 73017, HD 77247, RT Vir and 104 Her obtained by thefirst author with the Four College Automated Photoelectric Telescopewith of order 100 observations taken over two or more years. Four ofthese stars are Small-Amplitude Red Variables (SARVs). The primaryperiod of NZ Gem (M3 II-IIIs) is about 33.70 days. HD 77247, theshortest period barium star with spectral type K0, has a photometricperiod of about 82 days which is close to its binary period of 80.53days. Its check star HD 73017, a non-variable in B, V and R, is variablein I due most likely to a previously unknown cooler companion. RT Vir(M8 III) is found to be a multiperiodic star whose observations areconsistent with the 155 day primary period of Lebzelter & Hinkle(2002). 104 Her (M3 III) is also multiperiodic with a primary period of21.48 days.
| Analysis of the Na, Mg, Al, and Si Abundances in the Atmospheres of Red Giants of Different Spectral Subgroups
We analyze the Na, Mg, Al, and Si abundances in the atmospheres of morethan 40 stars, includingred giants of different spectral subgroups(normal red giants, mild and classical barium stars) and severalsupergiants. All these elements exhibit abundance excesses, with theoverabundance increasing with the star’s luminosity. Thedependence of the overabundances for each of these elements on theluminosity (or log g) is the same for all the spectral subgroups,testifying to a common origin: they are all products of hydrogen burningin the NeNa and MgAl cycles that have been dredged up from the stellarinteriors to the outer atmospheric layers by convection that graduallydevelops during the star’s evolution from the main sequence to thered-giant stage. The sodium abundances derived for several stars arelower than for other stars with similar atmospheric parameters. The agesand kinematic characteristics of these two groups of stars suggest thatthey probably belong to different stellar generations.
| Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters
The availability of the Hipparcos Catalogue has triggered many kinematicand dynamical studies of the solar neighbourhood. Nevertheless, thosestudies generally lacked the third component of the space velocities,i.e., the radial velocities. This work presents the kinematic analysisof 5952 K and 739 M giants in the solar neighbourhood which includes forthe first time radial velocity data from a large survey performed withthe CORAVEL spectrovelocimeter. It also uses proper motions from theTycho-2 catalogue, which are expected to be more accurate than theHipparcos ones. An important by-product of this study is the observedfraction of only 5.7% of spectroscopic binaries among M giants ascompared to 13.7% for K giants. After excluding the binaries for whichno center-of-mass velocity could be estimated, 5311 K and 719 M giantsremain in the final sample. The UV-plane constructed from these datafor the stars with precise parallaxes (σπ/π≤20%) reveals a rich small-scale structure, with several clumpscorresponding to the Hercules stream, the Sirius moving group, and theHyades and Pleiades superclusters. A maximum-likelihood method, based ona Bayesian approach, has been applied to the data, in order to make fulluse of all the available stars (not only those with precise parallaxes)and to derive the kinematic properties of these subgroups. Isochrones inthe Hertzsprung-Russell diagram reveal a very wide range of ages forstars belonging to these groups. These groups are most probably relatedto the dynamical perturbation by transient spiral waves (as recentlymodelled by De Simone et al. \cite{Simone2004}) rather than to clusterremnants. A possible explanation for the presence of younggroup/clusters in the same area of the UV-plane is that they have beenput there by the spiral wave associated with their formation, while thekinematics of the older stars of our sample has also been disturbed bythe same wave. The emerging picture is thus one of dynamical streamspervading the solar neighbourhood and travelling in the Galaxy withsimilar space velocities. The term dynamical stream is more appropriatethan the traditional term supercluster since it involves stars ofdifferent ages, not born at the same place nor at the same time. Theposition of those streams in the UV-plane is responsible for the vertexdeviation of 16.2o ± 5.6o for the wholesample. Our study suggests that the vertex deviation for youngerpopulations could have the same dynamical origin. The underlyingvelocity ellipsoid, extracted by the maximum-likelihood method afterremoval of the streams, is not centered on the value commonly acceptedfor the radial antisolar motion: it is centered on < U > =-2.78±1.07 km s-1. However, the full data set(including the various streams) does yield the usual value for theradial solar motion, when properly accounting for the biases inherent tothis kind of analysis (namely, < U > = -10.25±0.15 kms-1). This discrepancy clearly raises the essential questionof how to derive the solar motion in the presence of dynamicalperturbations altering the kinematics of the solar neighbourhood: doesthere exist in the solar neighbourhood a subset of stars having no netradial motion which can be used as a reference against which to measurethe solar motion?Based on observations performed at the Swiss 1m-telescope at OHP,France, and on data from the ESA Hipparcos astrometry satellite.Full Table \ref{taba1} is 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/430/165}
| Analysis of Atmospheric Abundances in Classical Barium Stars
We present our analysis of elemental abundances in the atmospheres of 16classical barium stars derived from high-resolution spectra and modelatmospheres. Comparison of the results with analogous data for moderatebarium stars and normal red giants shows that the abundance patterns forelements before the iron peak are the same for all three groups of redgiants, testifying to a similar origin. For binary systems, we confirmthe influence of the orbital period and, hence, the componentseparation, on the overabundance of s-process elements. The amount ofenrichment in s-process elements is also influenced by mass,metallicity, and evolutionary phase. Any of these parameters can beimportant in individual objects.
| Studies of Classical Barium Stars
Using atmosphere models based on high-resolution spectra, we havederived the abundances of chemical elements in the atmospheres of sevenclassical barium stars and compared them with the elemental abundancesof moderate barium stars and normal red giants. The behavior of elementsup to the iron peak is the same in all three groups of giants, providingevidence that they have a common origin. The dependence of the anomalousabundances of s-process elements on stellar mass and metallicity isqualitatively similar for all three groups, probably indicating that asubstantial role is played by the evolutionary phase of the stars. Weconclude that the barium-star phenomenon and the overabundances ofs-process elements in barium stars cannot be explained as a consequenceof binarity alone. The extent to which the s-process elements areoverabundant is affected by the mass, metallicity, and evolutionaryphase of the given star, and any of these parameters may prove to beimportant in a specific object.
| The heavy-element abundances of AGB stars and the angular momentum conservation model of wind accretion for barium stars
Adopting new s-process nucleosynthesis scenario and branch s-processpath, we calculate the heavy-element abundances of solar metallicity3Msun thermal pulse asymptotic giant branch (hereafterTP-AGB) stars, and then discuss the correlation between heavy-elementabundances and C/O ratio. 13C(alpha ,n)16Oreaction is the major neutron source, which is released in radiativecondition during the interpulse period, hence gives rise to an efficients-processing that depends on the 13C profile in the13C pocket. A second small neutron burst from 22Nesource marginally operates during convective pulses over previouslys-processed material diluted with fresh Fe seed and H-burning ashes. Thecalculated heavy-element abundances and C/O ratio on the surfaces of AGBstars are compared with the observations of MS, S and C (N-type) stars.The observations are characterized by a spread in neutron exposures:0.5-2.5 times of the corresponding exposures reached in the three zonesof the 13C pocket showed by Fig. 1 of Gallino et al. (1998).The evolutionary sequence from M to S to C stars is explained naturallyby the calculated heavy-element abundances and C/O ratio. Then theheavy-element abundances on the surfaces of TP-AGB stars are used tocalculate the heavy-element overabundances of barium stars, which aregenerally believed to belong to binary systems and their heavy-elementoverabundances are produced by the accreting material from thecompanions (the former TP-AGB stars and the present white dwarfs). Toachieve this, firstly, the change equations of binary orbital elementsare recalculated by taking the angular momentum conservation in place ofthe tangential momentum conservation, and the change of delta r/r termis considered; then the heavy-element overabundances of barium stars arecalculated, in a self-consistent manner, through wind accretion duringsuccessive pulsed mass ejection, followed by mixing. The calculatedrelationships of heavy-element abundances to orbital periods P of bariumstars can fit the observations within the error ranges. Moreover, thecalculated abundances of nuclei of different atomic charge Z,corresponding to different neutron exposures of TP-AGB stars, can fitthe observational heavy-element abundances of 14 barium stars in theerror ranges. Our results suggest that the barium stars with longerorbital period P>1600 d may form through accreting part of the ejectafrom the intrinsic AGB stars through stellar wind, and the massaccretion rate is in the range of 0.1-0.5 times of Bondi-Hoyle'saccretion rate. Those with shorter orbital period P<600 d may beformed through other scenarios: dynamically stable late case C masstransfer or common envelope ejection.
| The eccentricities of the barium stars
We investigate the eccentricities of barium (Baii) stars formed via astellar wind accretion model. We carry out a series of Monte Carlosimulations using a rapid binary evolution algorithm, which incorporatesfull tidal evolution, mass loss and accretion, and nucleosynthesis anddredge-up on the thermally pulsing asymptotic giant branch. We followthe enhancement of barium in the envelope of the accreting main-sequencecompanion and dilution into its convective envelope once the starascends the giant branch. The observed eccentricities of Baii stars aresignificantly smaller than those of an equivalent set of normal redgiants but are nevertheless non-zero. We show that such a distributionof eccentricities is consistent with a wind accretion model for Baiistar production with weak viscous tidal dissipation in the convectiveenvelopes of giant stars. We successfully model the distribution oforbital periods and the number of observed Baii stars. The actualdistribution of eccentricities is quite sensitive to the strength of thetides, so that we are able to confirm that this strength is close to,but less than, what is expected theoretically and found with alternativeobservational tests. Two systems - one very short-period but eccentric,and one long-period and highly eccentric - still lie outside theenvelope of our models, and so require a more exotic formationmechanism. All our models, even those which were a good fit to theobserved distributions, overproduced the number of high-period bariumstars, a problem that could not be solved by some combination of thethree parameters: tidal strength, tidal enhancement and wind accretionefficiency.
| 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).
| Catalogs of temperatures and [Fe/H] averages for evolved G and K stars
A catalog of mean values of [Fe/H] for evolved G and K stars isdescribed. The zero point for the catalog entries has been establishedby using differential analyses. Literature sources for those entries areincluded in the catalog. The mean values are given with rms errors andnumbers of degrees of freedom, and a simple example of the use of thesestatistical data is given. For a number of the stars with entries in thecatalog, temperatures have been determined. A separate catalogcontaining those data is briefly described. Catalog only available atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| A re-analysis of the heavy-element abundance of barium stars.
Not Available
| 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.
| Mesures de vitesses radiales. VIII. Accompagnement AU sol DU programme d'observation DU satellite HIPPARCOS
We publish 1879 radial velocities of stars distributed in 105 fields of4^{\circ} \times 4^{\circ}. We continue the PPO series \cite[(Fehrenbachet al. 1987;]{Feh87} \cite[Duflot et al. 1990, 1992 and 1995),]{Du90}using the Fehrenbach objective prism method. Table 1 only available inelectronic form at CDS via to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| 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.
| The formation of barium and CH stars and related objects
We investigate the formation of barium (Ba) and CH stars via binaryinteractions. We consider four evolutionary channels for theirformation: wind accretion, wind exposure, stable Roche lobe overflow(RLOF), and common-envelope (CE) ejection, and carry out Monte Carlosimulations. We explore the effects of model parameters, such as atidal-enhancement parameter for stellar wind, a maximum stellar mass fors-processing, and a minimum core mass for thermal pulsation, on ourresults. We also explore the effects of various assumptions about age,mass-ratio distribution and wind velocity. Our results show that binaryinteraction is successful in explaining the formation of Ba and CHstars. We successfully explain the distribution of orbital periods, thedistribution of mass functions, and the number of observed Ba stars. Wealso support the views (a) that a tidally enhanced stellar wind exists,(b) that thermal pulsation may begin at an earlier phase during theasymptotic giant branch (AGB) than is usually assumed, and (c) that themaximum stellar mass for s-processing is about 2 M_solar. We find thatthe degree of Ba pollution is strongly correlated with orbital period.The average mass of strong Ba stars is estimated to be 1.8 M_solar, andof all Ba stars 1.7 M_solar the average mass for the white dwarf (WD)companions in the Ba-star binaries is estimated to be 0.60 M_solar. Theaverage mass of strong CH stars is estimated to be 1.2 M_solar, and theaverage mass for their WD companions is estimated to be 0.62 M_solar.The total number of Ba stars in the Galaxy brighter than 10th apparentmagnitude is estimated to be 6000, while that of CH stars is much less.We also investigate the formation of pre-Ba/CH stars, cataclysmicvariables, Algols, double degenerates and symbiotics. Some encouragingresults are found, although much work needs to be done in order tounderstand fully their formation, especially of pre-Ba/CH stars and ofsymbiotics.
| 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.
| Radio continuum emission from stars: a catalogue update.
An updated version of my catalogue of radio stars is presented. Somestatistics and availability are discussed.
| Examination of the wind accretion scenario for barium stars
In this note, we confront the results of a spectroscopic analysis givings-process element abundances in a sample of barium stars withtheoretical predictions from the wind accretion scenario of Boffin &Jorissen (1988). This comparison is done in the overabundance-orbitaqlperiod plane.
| A Spectroscopic Analysis of Barium Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1994A&A...283..937Z&db_key=AST
| 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.
| Discovery of the first eclipsing binary barium star
Photometric monitoring of barium stars is discussed with particularattention given to the first eclipsing binary barium star, HD 46407. Thespectroscopic ephemeris of HD 46407 was used to predict the times of apossible eclipse of the companion by the barium star. It is concludedthat the light curve of HD 46407 derived from the photometricobservations in the D50 system displays a sharp 'primary' eclipse(companion behind the barium star) and a possible shallow 'secondary'eclipse. The primary eclipse occurred in November 1988 and had a depthof about 0.02 mag.
| 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.
| Radio-continuum observations of a variety of cool stars
Radio-continuum observations at 2 and 6 cm are presented for 26 coolstars (F0 and later), including 10 F-K main-sequence stars and 16 F-Mgiant and supergiant stars. The detection of two M giants, g Her and RLyr, is reported for the first time; a redetection of the unusualinfrared carbon star IRC + 10216 is also reported. Some generalconclusions are made concerning the radio-emission properties of thevarious types of cool stars observed. For both the detected andnondetected stars, constraints are obtained on the ionized component oftheir mass-loss rates.
| 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.
| Spectroscopical study of barium stars. IV. Chemical composition of HD 77247, 130386, 131670, 139409, 202109, 218356.
Not Available
| The Perkins catalog of revised MK types for the cooler stars
A catalog is presented listing the spectral types of the G, K, M, and Sstars that have been classified at the Perkins Observatory in therevised MK system. Extensive comparisons have been made to ensureconsistency between the MK spectral types of stars in the Northern andSouthern Hemispheres. Different classification spectrograms have beengradually improved in spite of some inherent limitations. In thecatalog, the full subclasses used are the following: G0, G5, G8, K0, K1,K2, K3, K4, K5, M0, M1, M2, M3, M4, M5, M6, M7, and M8. Theirregularities are the price paid for keeping the general scheme of theoriginal Henry Draper classification.
| 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 Study of Barium Stars - Part Two - Chemical Composition of HD16458 HD204075 HD199394 HD199939 and HD196678
Not Available
| 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.
| Can a barium star be produced by wind accretion in a detached binary?
Using the example of Zeta Capricorni, it is shown that the windaccretion model is better suited than Roche lobe overflow scenarios forexplaining barium stars. In the model, it is assumed that barium starsresult from the accretion of part of the matter ejected through a windand a planetary nebula by a heavy element-rich asymptotic branch star.It is found that the contamination of the barium star depends only onthe present values of the orbital separation and of the mass of thewhite dwarf companion.
|
提交文章
相关链接
提交链接
下列团体成员
|
观测天体数据
目录:
|
