Tartalom
Képek
Kép feltöltése
DSS Images Other Images
Kapcsolódó cikkek
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}
| The Indo-US Library of Coudé Feed Stellar Spectra
We have obtained spectra for 1273 stars using the 0.9 m coudéfeed telescope at Kitt Peak National Observatory. This telescope feedsthe coudé spectrograph of the 2.1 m telescope. The spectra havebeen obtained with the no. 5 camera of the coudé spectrograph anda Loral 3K×1K CCD. Two gratings have been used to provide spectralcoverage from 3460 to 9464 Å, at a resolution of ~1 Å FWHMand at an original dispersion of 0.44 Å pixel-1. For885 stars we have complete spectra over the entire 3460 to 9464 Åwavelength region (neglecting small gaps of less than 50 Å), andpartial spectral coverage for the remaining stars. The 1273 stars havebeen selected to provide broad coverage of the atmospheric parametersTeff, logg, and [Fe/H], as well as spectral type. The goal ofthe project is to provide a comprehensive library of stellar spectra foruse in the automated classification of stellar and galaxy spectra and ingalaxy population synthesis. In this paper we discuss thecharacteristics of the spectral library, viz., details of theobservations, data reduction procedures, and selection of stars. We alsopresent a few illustrations of the quality and information available inthe spectra. The first version of the complete spectral library is nowpublicly available from the National Optical Astronomy Observatory(NOAO) via ftp and http.
| Synthetic Lick Indices and Detection of α-enhanced Stars. II. F, G, and K Stars in the -1.0 < [Fe/H] < +0.50 Range
We present an analysis of 402 F, G, and K solar neighborhood stars, withaccurate estimates of [Fe/H] in the range -1.0 to +0.5 dex, aimed at thedetection of α-enhanced stars and at the investigation of theirkinematical properties. The analysis is based on the comparison of 571sets of spectral indices in the Lick/IDS system, coming from fourdifferent observational data sets, with synthetic indices computed withsolar-scaled abundances and with α-element enhancement. We useselected combinations of indices to single out α-enhanced starswithout requiring previous knowledge of their main atmosphericparameters. By applying this approach to the total data set, we obtain alist of 60 bona fide α-enhanced stars and of 146 stars withsolar-scaled abundances. The properties of the detected α-enhancedand solar-scaled abundance stars with respect to their [Fe/H] values andkinematics are presented. A clear kinematic distinction betweensolar-scaled and α-enhanced stars was found, although a one-to-onecorrespondence to ``thin disk'' and ``thick disk'' components cannot besupported with the present data.
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable 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/qcar?J/A+A/367/521
| Two K Giants with Supermeteoritic Lithium Abundances: HDE 233517 and HD 9746
Two unusual Li-rich K giants, HDE 233517 and HD 9746, have been studied.Optical spectroscopy and photometry have been obtained to determine thefundamental parameters of HDE 233517, a single K2 III with an extremelylarge infrared excess. The spectra yield Teff=4475 K,logg=2.25, [Fe/H]=-0.37, vsini=17.6 km s-1, and a non-LTElogɛ(7Li)=4.22. Photometric observations reveallow-amplitude light variability with a period of 47.9 days. Combinedwith other parameters, this results in a minimum radius of 16.7Rsolar and minimum distance of 617 pc. Comparison of spectraobtained in 1994 and 1996 show profile variations in Hα and the NaD lines indicative of changing mass loss. Optical spectra of HD 9746, achromospherically active giant, were analyzed. The Teff=4400K and revised Hipparcos-based gravity of logg=2.30 lead to a non-LTElogɛ(7Li)=3.75. The Li abundances in both stars aresupermeteoritic. By the inclusion and exclusion of 6Li in thesyntheses, we show that consistent 7Li abundances areobtained only when 6Li is absent in the synthetic fit. Thisprovides evidence for fresh 7Li production and excludes bothpreservation of primordial Li and planetary accretion as viablescenarios for the formation of Li-rich giants. Both stars lie in closeproximity to the red giant luminosity bump supporting the hypothesisthat 7Li production is caused by the same mixing mechanismthat later results in CN processing and lowers the12C/13C ratio to nonstandard values.
| Rotation and lithium in single giant stars
In the present work, we study the link between rotation and lithiumabundance in giant stars of luminosity class III, on the basis of alarge sample of 309 single stars of spectral type F, G and K. We havefound a trend for a link between the discontinuity in rotation at thespectral type G0III and the behavior of lithium abundances around thesame spectral type. The present work also shows that giant starspresenting the highest lithium contents, typically stars earlier thanG0III, are those with the highest rotation rates, pointing for adependence of lithium content on rotation, as observed for otherluminosity classes. Giant stars later than G0III present, as a rule, thelowest rotation rates and lithium contents. A large spread of about fivemagnitudes in lithium abundance is observed for the slow rotators.Finally, single giant stars with masses 1.5 < M/Msun<=2.5 show a clearest trend for a correlation between rotational velocityand lithium abundance. Based on observations collected at theObservatoire de Haute -- Provence (France) and at the European SouthernObservatory, La Silla (Chile). Table 2 is only available electronicallywith the On-Line publication athttp://link.springer.de/link/service/00230/
| The Nature of the lithium rich giants. Mixing episodes on the RGB and early-AGB
We present a critical analysis of the nature of the so-called Li-richRGB stars. For a majority of the stars, we have used Hipparcosparallaxes to determine masses and evolutionary states by comparingtheir position on the Hertzsprung-Russell diagram with theoreticalevolutionary tracks. Among the twenty Li-rich giants whose location onthe HR diagram we were able to determine precisely, five appear to beLi-rich because they have not completed the standard first dredge-updilution, and three have abundances compatible with the maximum allowedby standard dilution. Thus, these should be re-classified as Li-normal.For the remaining stars, the high Li abundance must be a result of freshsynthesis of this fragile element. We identify two distinct episodes ofLi production which occur in advanced evolutionary phases depending uponthe mass of the star. Low-mass RGB stars, which later undergo the heliumflash, produce Li at the phase referred to as the bump in the luminosityfunction. At this evolutionary phase, the outwardly-moving hydrogenshell burns through the mean molecular weight discontinuity created bythe first dredge-up. Any extra-mixing process can now easily connect the3He-rich envelope material to the outer regions of thehydrogen-burning shell, enabling Li production by the Cameron &Fowler (1971) process. While very high Li abundances are then reached,this Li-rich phase is extremely short lived because once the mixingextends deep enough to lower the carbon isotopic ratio below thestandard dilution value, the freshly synthesized Li is quicklydestroyed. In intermediate-mass stars, the mean molecular weightgradient due to the first dredge-up is not erased until after the starhas begun to burn helium in its core. The Li-rich phase in these starsoccurs when the convective envelope deepens at the base of the AGB,permitting extra-mixing to play an effective role. Li production ceaseswhen a strong mean molecular weight gradient is built up between thedeepening convective envelope and the shell of nuclear burning thatsurrounds the inert CO core. This episode is also very short lived.Low-mass stars may undergo additional mixing at this phase. The compileddata provide constraints on the time scales for extra mixing and someinsight on processes suggested in the literature. However, our resultsdo not suggest any specific trigger mechanism. Since the Li-rich phasesare extremely short, enrichment of the Li content of the ISM as a resultof these episodes is negligible.
| A catalog of rotational and radial velocities for evolved stars
Rotational and radial velocities have been measured for about 2000evolved stars of luminosity classes IV, III, II and Ib covering thespectral region F, G and K. The survey was carried out with the CORAVELspectrometer. The precision for the radial velocities is better than0.30 km s-1, whereas for the rotational velocity measurementsthe uncertainties are typically 1.0 km s-1 for subgiants andgiants and 2.0 km s-1 for class II giants and Ib supergiants.These data will add constraints to studies of the rotational behaviourof evolved stars as well as solid informations concerning the presenceof external rotational brakes, tidal interactions in evolved binarysystems and on the link between rotation, chemical abundance and stellaractivity. In this paper we present the rotational velocity v sin i andthe mean radial velocity for the stars of luminosity classes IV, III andII. Based on observations collected at the Haute--Provence Observatory,Saint--Michel, France and at the European Southern Observatory, LaSilla, Chile. Table \ref{tab5} also available in electronic form at CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| 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
| Late-type giants with infrared excess. I. Lithium abundances
de la Reza et al. (1997) suggested that all K giants become Li-rich fora short time. During this period the giants are associated with anexpanding thin circumstellar shell supposedly triggered by an abruptinternal mixing mechanism resulting in the surface Li enrichment. Inorder to test this hypothesis twenty nine late-type giants withfar-infrared excess from the list of Zuckerman et al. (1995) wereobserved in the Li-region to study the connection between thecircumstellar shells and Li abundance. Eight giants have been found tohave log epsilon (Li) > 1.0. In the remaining giants the Li abundanceis found to be much lower. HD 219025 is found to be a rapidly rotating(projected rotational velocity of 23 +/-3 km s(-1) ), dusty and Li-rich(log epsilon (Li) = 3.0+/-0.2) K giant. Absolute magnitude derived fromthe Hipparcos parallax reveals that it is a giant and not apre-main-sequence star. The evolutionary status of HD 219025 seems to besimilar to that of HDE 233517 which is also a rapidly rotating, dustyand Li-rich K giant. The Hipparcos parallaxes of all the well studiedLi-rich K giants show that most of them are brighter than the ``clump"giants. Their position in the H-R diagram indicates that they have gonethrough mixing and the initial abundance of Li is not preserved. Thereseems to be no correlations between Li abundances, rotational velocitiesand carbon isotope ratios. The only satisfactory explanation for theoverabundance of lithium in these giants is the creation of Li by theextra deep mixing and the associated ``cool bottom processing". Based onobservations obtained at the European Southern Observatory, La Silla,Chile, and at the Observatoire de Haute Provence, France.
| Statistical equilibrium of lithium in the atmospheres of late-type stars: lithium-rich G-K giants.
Not Available
| On a Rapid Lithium Enrichment and Depletion of K Giant Stars
A model scenario has recently been introduced by de la Reza andcolleagues to explain the presence of very strong Li lines in thespectra of some low-mass K giant stars. In this scenario all ordinary,Li-poor, K giants become Li rich during a short time (~105 yr) whencompared to the red giant phase of 5 x 107 yr. In this "Li period," alarge number of the stars are associated with an expanding thincircumstellar shell supposedly triggered by an abrupt internal mixingmechanism resulting in a surface new 7Li enrichment. This Letterpresents nearly 40 Li-rich K giants known up to now. The distribution ofthese Li-rich giants, along with 41 other observed K giants that haveshells but are not Li rich, in a color-color IRAS diagram confirms thisscenario, which indicates, also as a new result, that a rapid Lidepletion takes place on a timescale of between ~103 and 105 yr. Thismodel explains the problem of the presence of K giants with far-infraredexcesses presented by Zuckerman and colleagues. Other present and futuretests of this scenario are briefly discussed.
| 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
| Lithium Enrichment--Mass-Loss Connection in K Giant Stars
Based on observed far-infrared properties of K giant stars, we propose ascenario linking the high Li abundances of some of these stars to theevolution of circumstellar shells. In this model, every K giant withmasses between 1.0 and 2.5 Mȯ become Li rich during the red giantbranch stage, and the internal mechanism responsible for the Lienrichment will initiate a prompt mass-loss event. The evolutionarypaths of the detached shells are compatible with observations for lowexpansion velocities of the order of 2 km s-1 and mass loss of (2--5) x10-8 Mȯ yr-1. This modest mass loss is, however, 2 orders ofmagnitude larger than those of normal, Li-poor K giants. A "Li time" ofthe order of 80,000 yr or somewhat larger is possible. This Li phase is,nevertheless, not related to the 12C/13C ratio which appears to evolve,for these low-mass stars, over a much longer time. This model requires arapid internal process of Li enrichment and depletion. New argumentsappearing in the literature concerning this internal process arediscussed. Reference is also made to the importance of these stars tothe Galactic Li evolution.
| Rotational velocity for lithium-rich evolved stars.
Precise rotational velocities have been determined for 12 lithium-richgiant stars using the CORAVEL spectrometer. Except for HD 9746, thelithium-rich giants show normal rotational velocities with respect totypical lithium-normal giants of the same spectral type. Further, wehave found no sign of binarity for the lithium-rich giants.
| Li-rich giants: evidence for convection mixing
Not Available
| The Li K giant stars
Not Available
| Carbon Isotope Ratios in Very Lithium-Rich K Giants
High-resolution spectra were used to derive CNO abundances and the12C/13C ratios for the very Li-rich K giants HD 19745 and HD 39853. Oand 12C/13C are also obtained for comparison for the Li-rich K giant HD787. Results from the literature for other very Li-rich giants were alsogathered to allow for a more complete discussion. The three most Li-richgiants known, HD 19745, HD 39853, and HD 95799, with epsilon (Li) >=3.0, show low 12C/13C values (12C/13C <= 15), requiring anextra-mixing mechanism, whereas HD 9746 and HD 112127 with epsilon (Li)~ 2.7 show 12C/13C ~ 25, following the standard first dredge-uppredictions. The data for these five stars indicate that no clearcorrelation is found between 12C/13C and epsilon (Li) for the veryLi-rich giants. An important conclusion is that, since for the threemost Li-rich giants, 12C/13C is low, efficient mixing should havelowered both 12C/13C and Li abundances. The very high Li abundancesactually found in these stars call therefore for an independentmechanism enriching the Li.
| 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.
| CNO Abundances and 12/C/13/C Ratios in the Atmospheres of Lithium-Rich Giants
Not Available
| Lithium and rapid rotation in chromospherically active single giants
The rotational velocities presently obtained via spectroscopicobservations of a group of moderately rapidly rotating, chomosphericallyactive single giants indicate that Gray's (1989) rotostat hypothesisrequires modification. Their rapid rotation appears to be due to high Liabundances, and results in increased chromospheric activity. A scenariois projected in which the surface convection zone reaches the rapidlyrotating core just as a star begins its first ascent of the giantbranch, and dredges both high angular momentum material and freshlysynthesized Li to the surface.
| Fourth preliminary catalogue of stars, right ascension observed with photoelectric transit instrument (PPCP4).
Not Available
| A critical appraisal of published values of (Fe/H) for K II-IV stars
'Primary' (Fe/H) averages are presented for 373 evolved K stars ofluminosity classes II-IV and (Fe/H) values beween -0.9 and +0.21 dex.The data define a 'consensus' zero point with a precision of + or -0.018 dex and have rms errors per datum which are typically 0.08-0.16dex. The primary data base makes recalibration possible for the large(Fe/H) catalogs of Hansen and Kjaergaard (1971) and Brown et al. (1989).A set of (Fe/H) standard stars and a new DDO calibration are given whichhave rms of 0.07 dex or less for the standard star data. For normal Kgiants, CN-based values of (Fe/H) turn out to be more precise than manyhigh-dispersion results. Some zero-point errors in the latter are alsofound and new examples of continuum-placement problems appear. Thushigh-dispersion results are not invariably superior to photometricmetallicities. A review of high-dispersion and related work onsupermetallicity in K III-IV star is also given.
| High-resolution spectroscopic survey of 671 GK giants. I - Stellar atmosphere parameters and abundances
A high-resolution spectroscopic survey of 671 G and K field giants isdescribed. Broad-band Johnson colors have been calibrated againstrecent, accurate effective temperature, T(eff), measurements for starsin the range 3900-6000 K. A table of polynomial coefficients for 10color-T(eff) relations is presented. Stellar atmosphere parameters,including T(eff), log g, Fe/H, and microturbulent velocity, are computedfor each star, using the high-resolution spectra and various publishedphotometric catalogs. For each star, elemental abundances for a varietyof species have been computed using a LTE spectrum synthesis program andthe adopted atmosphere parameters.
| A search for lithium-rich giant stars
Lithium abundances or upper limits have been determined for 644 brightG-K giant stars selected from the DDO photometric catalog. Two of thesegiants possess surface lithium abundances approaching the 'cosmic' valueof the interstellar medium and young main-sequence stars, and eight moregiants have Li contents far in excess of standard predictions. At leastsome of these Li-rich giants are shown to be evolved to the stage ofhaving convectively mixed envelopes, either from the direct evidence oflow surface carbon isotope ratios, or from the indirect evidence oftheir H-R diagram positions. Suggestions are given for the uniqueconditions that might have allowed these stars to produce or accrete newlithium for their surface layers, or simply to preserve from destructiontheir initial lithium contents. The lithium abundance of the remainingstars demonstrates that giants only very rarely meet the expectations ofstandard first dredge-up theories; the average extra Li destructionrequired is about 1.5 dex. The evolutionary states of these giants andtheir average masses are discussed briefly, and the Li distribution ofthe giants is compared to predictions of Galactic chemical evolution.
| 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.
| Transformation equations and other aids for VRI photometry
Transformations among VRI systems are commonly beset by Paschen-jumpeffects, for which fully satisfactory allowance has not previously beenmade. This paper describes two new techniques which are based on thework of Gutierrez-Moreno, and which allow fully for the effects of thePaschen jump. Values of E(V-R)/E(B-V) and E(R-I)/E(B-V) are also givenfor the Cousins system for a wide range of temperatures. These and thenew techniques contribute to a set of new transformation relations whichapply for most VRI systems; the status of the remaining systems isreviewed, and future work needed for them is described. Two majorsources of Cousins VRI data underlie the new relations; the consistencyof these sources is reviewed and found to be generally satisfactory,although more work on this question is needed. Finally, three tables oftransformed standard-star and other data are given for the Cousins andJohnson systems, and a description of ways to reproduce the latter ispresented.
| 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
| Radial velocities of a random sample of K giant stars and implications concerning multiplicity among giant stars in clusters
Radial velocities, with precisions better than 0.40 km/sec have beenobtained for a random sample of 40 K giant stars. The frequency osspectroscopic binaries detected in this sample from observations over a3 year time span is 15% to 20%, and more are probably long-periodbinaries. A comparison is made between this sample and others includingthe sample of giants measured by Gunn and Griffin (1979) in the globularcluster M3. The comparison with M3 indicates that, when allowance ismade for the sizes and masses of the stars, there is no evidence frompublished velocity data that M3 is deficient in binaries.
| The binary nature of the barium stars
Radial-velocity spectrometer observations are presented that indicatethat Ba II stars are binary systems. The secondary stars of thesesystems have low masses, consistent with their being degenerate objectswhich have lost mass onto their primaries in a previous stage ofevolution. It is suggested that the Population II equivalents, the CHstars, may also be binary systems. This may be related to the fact thatthey are found only in globular clusters of the lowest centralconcentration.
|
Új cikk hozzáadása
Kapcsolódó hivatkozások
- - (nincs kapcsolódó hivatkozás) -
Új link hozzáadása
Besorolás csoportokba:
|
Pozíciós és asztrometriai adatok
| Csillagkép: | Sárkány |
| Rektaszcenzió: | 16h21m48.70s |
| Deklináció: | +69°06'34.0" |
| Vizuális fényesség: | 5.25 |
| Távolság: | 90.171 parszek |
| RA sajátmozgás: | -19.3 |
| Dec sajátmozgás: | -8.8 |
| B-T magnitude: | 6.69 |
| V-T magnitude: | 5.388 |
Katalógusok és elnevezések:
|
