Ýçindekiler
Görüntüler
Resim Yükleyin
DSS Images Other Images
Ýlgili Makaleler
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
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| Metallicity and absolute magnitude calibrations for UBV photometry
Calibrations are presented here for metallicity ([Fe/H]) in terms of theultraviolet excess, [δ(U - B) at B - V = 0.6, hereafterδ0.6], and also for the absolute visual magnitude(MV) and its difference with respect to the Hyades(ΔMHV) in terms of δ0.6 and(B - V), making use of high-resolution spectroscopic abundances from theliterature and Hipparcos parallaxes. The relation[Fe/H]-δ0.6 has been derived for dwarf plus turn-offstars, and also for dwarf, turn-off, plus subgiant stars classifiedusing the MV-(B - V)0 plane of Fig. 11, which iscalibrated with isochrones from Bergbusch & VandenBerg (and alsoVandenBerg & Clem). The [Fe/H]-δ0.6 relations inour equations (5) and (6) agree well with those of Carney, as can beseen from Fig. 5(a). Within the uncertainties, the zero-points,+0.13(+/-0.05) of equation (5) and +0.13(+/-0.04) of equation (6), arein good agreement with the photometric ones of Cameron and of Carney,and close to the spectroscopic ones of Cayrel et al. and of Boesgaard& Friel for the Hyades open cluster. Good quantitative agreementbetween our estimated [Fe/H] abundances with those from uvby-βphotometry and spectroscopic [Fe/H]spec values demonstratesthat our equation (6) can be used in deriving quality photometric metalabundances for field stars and clusters using UBV data from variousphotometric surveys.For dwarf and turn-off stars, a new hybrid MV calibration ispresented, based on Hipparcos parallaxes withσπ/π <= 0.1 and with a dispersion of +/-0.24in MV. This hybrid MV calibration containsδ0.6 and (B - V) terms, plus higher order cross-termsof these, and is valid for the ranges of +0.37 <= (B - V)0<= +0.88,- 0.10 <= δ0.6 <= +0.29 and 3.44<= MV <= 7.23. For dwarf and turn-off stars, therelation for ΔMHV is revised and updated interms of (B - V) and δ0.6, for the ranges of -0.10<= δ0.6 <= +0.29, and +0.49 <= (B -V)0 <= +0.89, again making use of Hipparcos parallaxeswith σπ/π <= 0.1. These parallaxes formetal-poor dwarf and turn-off stars in our sample reveal that thedifference of ΔMHV(B - V) relative to Hyadesat (B - V) = +0.70 should be 1.37mag, instead of the 1.58mag given byLaird et al. In general, Hipparcos parallaxes are larger thanground-based ones, causing a divergence of ourΔMHV(B - V,δ0.6) relation(the solid line in Fig. 15b), from the one of Laird et al. (the dashedline) for the range +0.10 <= δ0.6 <= +0.29 ourabsolute magnitudes are fainter, as has been confirmed for localsubdwarfs by Reid. Our final calibrations forΔMHV(B - V, δ0.6),equations (16) and (17), are third-order polynomials inδ0.6, pass through the origin, and provide photometricdistances in reasonable agreement with those obtained directly fromHipparcos parallaxes (Fig. 18).
| Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 pc-The Southern Sample
We are obtaining spectra, spectral types, and basic physical parametersfor the nearly 3600 dwarf and giant stars earlier than M0 in theHipparcos catalog within 40 pc of the Sun. Here we report on resultsfor 1676 stars in the southern hemisphere observed at Cerro TololoInter-American Observatory and Steward Observatory. These resultsinclude new, precise, homogeneous spectral types, basic physicalparameters (including the effective temperature, surface gravity, andmetallicity [M/H]), and measures of the chromospheric activity of ourprogram stars. We include notes on astrophysically interesting stars inthis sample, the metallicity distribution of the solar neighborhood, anda table of solar analogs. We also demonstrate that the bimodal nature ofthe distribution of the chromospheric activity parameterlogR'HK depends strongly on the metallicity, andwe explore the nature of the ``low-metallicity'' chromosphericallyactive K-type dwarfs.
| Effective temperature scale and bolometric corrections from 2MASS photometry
We present a method to determine effective temperatures, angularsemi-diameters and bolometric corrections for population I and II FGKtype stars based on V and 2MASS IR photometry. Accurate calibration isaccomplished by using a sample of solar analogues, whose averagetemperature is assumed to be equal to the solar effective temperature of5777 K. By taking into account all possible sources of error we estimateassociated uncertainties to better than 1% in effective temperature andin the range 1.0-2.5% in angular semi-diameter for unreddened stars.Comparison of our new temperatures with other determinations extractedfrom the literature indicates, in general, remarkably good agreement.These results suggest that the effective temperaure scale of FGK starsis currently established with an accuracy better than 0.5%-1%. Theapplication of the method to a sample of 10 999 dwarfs in the Hipparcoscatalogue allows us to define temperature and bolometric correction (Kband) calibrations as a function of (V-K), [m/H] and log g. Bolometriccorrections in the V and K bands as a function of T_eff, [m/H] and log gare also given. We provide effective temperatures, angularsemi-diameters, radii and bolometric corrections in the V and K bandsfor the 10 999 FGK stars in our sample with the correspondinguncertainties.
| Abundances of Mn, Co and Eu in a sample of 20 F-G disk stars: the influence of hyperfine structure splitting
We present Mn, Co and Eu abundances for a sample of 20 disk F and Gdwarfs and subgiants with metallicities in the range-0.8≤[Fe/H]≤+0.3. We investigate the influence of hyperfinestructure (HFS) on the derived abundances of Mn and Co by using HFS datafrom different sources in the literature, as well as calculated HFS frominteraction factors A and B. Eu abundances were obtained from spectralsynthesis of one Eu II line that takes into account HFS from a series ofrecent laboratory measurements. For the lines analysed in this study, wefind that for manganese, the differences between abundances obtainedwith different HFSs are no greater than 0.10 dex. Our cobalt abundancesare even less sensitive to the choice of HFS than Mn, presenting a 0.07dex maximum difference between determinations with different HFSs.However, the cobalt HFS data from different sources are significantlydifferent. Our abundance results for Mn offer an independentconfirmation of literature results, favouring type Ia supernovae as themain nucleosynthesis site of Mn production, in contrast to trends of Mnversus metallicity previously reported in the literature. For Co, weobtain [Co/Fe]0.0 in the range -0.3<[Fe/H]<+0.3 and [Co/Fe]rising to a level of +0.2 when [Fe/H] decreases from -0.3 to -0.8, indisagreement with recent results in the literature. The observeddiscrepancies may be attributed to the lack of HFS in the works we usedfor comparison. Our results for Eu are in accordance with low-mass typeII supernovae being the main site of the r-process nucleosynthesis.
| The age of the Galactic thin disk from Th/Eu nucleocosmochronology. I. Determination of [Th/Eu] abundance ratios
The purpose of this work is to resume investigation of Galactic thindisk dating using nucleocosmochronology with Th/Eu stellar abundanceratios, a theme absent from the literature since 1990. A stellar sampleof 20 disk dwarfs/subgiants of F5 to G8 spectral types with-0.8≤[Fe/H]≤+0.3 was selected. In stars with such spectral typesand luminosity classes, spectral synthesis techniques must be employedif we wish to achieve acceptably accurate results. An homogeneous,self-consistent set of atmospheric parameters was determined. Effectivetemperatures were determined from photometric calibrations and Hαprofile fitting; surface gravities were obtained from Teff,stellar masses and luminosities; microturbulence velocities andmetallicities were obtained from detailed, differential spectroscopicanalysis, relative to the Sun, using equivalent widths of Fe I and Fe IIlines. Chemical abundances of the elements that contaminate the Th andEu spectral regions (Ti, V, Cr, Mn, Co, Ni, Ce, Nd, and Sm) weredetermined through spectroscopic analysis. Abundance uncertainties werethoroughly scrutinised, their average value (0.10±0.02) dex being found to be satisfactorily low. Eu and Th abundances weredetermined by spectral synthesis of one Eu II line (4129.72 Å) andone Th II line (4019.13 Å), taking into account the detailedhyperfine structures of contaminating Co lines, as well as the hyperfinestructure and isotope shift of the Eu line. Comparison of our abundanceswith literature data shows that our results exhibit a similar behaviour,but a considerably lower scatter (36% lower for Eu, and 61% lower forTh). The [Th/Eu] abundance ratios thus obtained were used, in the secondpaper of this series, to determine the age of the Galactic disk.
| 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
| Statistical cataloging of archival data for luminosity class IV-V stars. II. The epoch 2001 [Fe/H] catalog
This paper describes the derivation of an updated statistical catalog ofmetallicities. The stars for which those metallicities apply are ofspectral types F, G, and K, and are on or near the main sequence. Theinput data for the catalog are values of [Fe/H] published before 2002February and derived from lines of weak and moderate strength. Theanalyses used to derive the data have been based on one-dimensional LTEmodel atmospheres. Initial adjustments which are applied to the datainclude corrections to a uniform temperature scale which is given in acompanion paper (see Taylor \cite{t02}). After correction, the data aresubjected to a statistical analysis. For each of 941 stars considered,the results of that analysis include a mean value of [Fe/H], an rmserror, an associated number of degrees of freedom, and one or moreidentification numbers for source papers. The catalog of these resultssupersedes an earlier version given by Taylor (\cite{t94b}).Catalog is only available in electronic form at the CDS via anonymousftp cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/398/731
| Statistical cataloging of archival data for luminosity class IV-V stars. I. The epoch 2001 temperature catalog
This paper is one of a pair in which temperatures and metallicitycatalogs for class IV-V stars are considered. The temperature catalogdescribed here is derived from a calibration based on stellar angulardiameters. If published calibrations of this kind are compared by usingcolor-index transformations, temperature-dependent differences among thecalibrations are commonly found. However, such differences are minimizedif attention is restricted to calibrations based on Johnson V-K. Acalibration of this sort from Di Benedetto (\cite{dib98}) is thereforetested and adopted. That calibration is then applied to spectroscopicand photometric data, with the latter predominating. Cousins R-Iphotometry receives special attention because of its high precision andlow metallicity sensitivity. Testing of temperatures derived from thecalibration suggests that their accuracy and precision are satisfactory,though further testing will be warranted as new results appear. Thesetemperatures appear in the catalog as values of theta equiv5040/T(effective). Most of these entries are accompanied by measured orderived values of Cousins R-I. Entries are given for 951 stars.Catalog is only available in electronic form 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/398/721
| Improved Astrometry and Photometry for the Luyten Catalog. II. Faint Stars and the Revised Catalog
We complete construction of a catalog containing improved astrometry andnew optical/infrared photometry for the vast majority of NLTT starslying in the overlap of regions covered by POSS I and by the secondincremental Two Micron All Sky Survey (2MASS) release, approximately 44%of the sky. The epoch 2000 positions are typically accurate to 130 mas,the proper motions to 5.5 mas yr-1, and the V-J colors to0.25 mag. Relative proper motions of binary components are measured to 3mas yr-1. The false-identification rate is ~1% for11<~V<~18 and substantially less at brighter magnitudes. Theseimprovements permit the construction of a reduced proper-motion diagramthat, for the first time, allows one to classify NLTT stars intomain-sequence (MS) stars, subdwarfs (SDs), and white dwarfs (WDs). We inturn use this diagram to analyze the properties of both our catalog andthe NLTT catalog on which it is based. In sharp contrast to popularbelief, we find that NLTT incompleteness in the plane is almostcompletely concentrated in MS stars, and that SDs and WDs are detectedalmost uniformly over the sky δ>-33deg. Our catalogwill therefore provide a powerful tool to probe these populationsstatistically, as well as to reliably identify individual SDs and WDs.
| New Metallicity Calibration Down to [Fe/H] = -2.75 dex
We have taken 88 dwarfs, covering the colour-index interval 0.37 <=(B-V)0 <= 1.07mag, with metallicities -2.70 <= [Fe/H]<= +0.26dex, from three different sources for new metallicitycalibration. The catalogue of Cayrel de Stroble et al. (2001), whichincludes 65% of the stars in our sample, supplies detailed informationon abundances for stars with determination based on high-resolutionspectroscopy. In constructing the new calibration we have used as`corner stones' 77 stars which supply at least one of the followingconditions: (i) the parallax is larger than 10mas (distance relative tothe Sun less than 100pc) and the galactic latitude is absolutely higherthan 30° (ii) the parallax is rather large, if the galactic latitudeis absolutely low and vice versa. Contrary to previous investigations, athird-degree polynomial is fitted for the new calibration: [Fe/H]=0.10 -2.76δ - 24.04δ2 + 30.00δ3. Thecoefficients were evaluated by the least-squares method, without regardto the metallicity of Hyades. However, the constant term is in the rangeof metallicity determined for this cluster, i.e.0.08<=[Fe/H]<=0.11dex. The mean deviation and the mean error inour work are equal to those of Carney (1979), for [Fe/H] >= -1.75dexwhere Carney's calibration is valid
| HIPPARCOS age-metallicity relation of the solar neighbourhood disc stars
We derive age-metallicity relations (AMRs) and orbital parameters forthe 1658 solar neighbourhood stars to which accurate distances aremeasured by the HIPPARCOS satellite. The sample stars comprise 1382 thindisc stars, 229 thick disc stars, and 47 halo stars according to theirorbital parameters. We find a considerable scatter for thin disc AMRalong the one-zone Galactic chemical evolution (GCE) model. Orbits andmetallicities of thin disc stars show now clear relation each other. Thescatter along the AMR exists even if the stars with the same orbits areselected. We examine simple extension of one-zone GCE models whichaccount for inhomogeneity in the effective yield and inhomogeneous starformation rate in the Galaxy. Both extensions of the one-zone GCE modelcannot account for the scatter in age - [Fe/H] - [Ca/Fe] relationsimultaneously. We conclude, therefore, that the scatter along the thindisc AMR is an essential feature in the formation and evolution of theGalaxy. The AMR for thick disc stars shows that the star formationterminated 8 Gyr ago in the thick disc. As already reported by Grattonet al. (\cite{Gratton_et.al.2000}) and Prochaska et al.(\cite{Prochaska_et.al.2000}), thick disc stars are more Ca-rich thanthin disc stars with the same [Fe/H]. We find that thick disc stars showa vertical abundance gradient. These three facts, the AMR, verticalgradient, and [Ca/Fe]-[Fe/H] relation, support monolithic collapseand/or accretion of satellite dwarf galaxies as likely thick discformation scenarios. Tables 2 and 3 are 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/394/927
| Catalogue of [Fe/H] determinations for FGK stars: 2001 edition
The catalogue presented here is a compilation of published atmosphericparameters (Teff, log g, [Fe/H]) obtained from highresolution, high signal-to-noise spectroscopic observations. This newedition has changed compared to the five previous versions. It is nowrestricted to intermediate and low mass stars (F, G and K stars). Itcontains 6354 determinations of (Teff, log g, [Fe/H]) for3356 stars, including 909 stars in 79 stellar systems. The literature iscomplete between January 1980 and December 2000 and includes 378references. The catalogue is made up of two tables, one for field starsand one for stars in galactic associations, open and globular clustersand external galaxies. The catalogue is distributed through the CDSdatabase. Access to the catalogue with cross-identification to othersets of data is also possible with VizieR (Ochsenbein et al.\cite{och00}). The catalogue (Tables 1 and 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/373/159 and VizieRhttp://vizier.u-strasbg.fr/.
| 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
| 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.
| Spectroscopic Follow-Up of Large Proper-Motion Stars in ESO Areas 207, 439, and 440
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....109.2817R&db_key=AST
| The general catalogue of trigonometric [stellar] paralaxes
Not Available
| Stroemgren photometry of F- and G-type stars brighter than V = 9.6. I. UVBY photometry
Within the framework of a large photometric observing program, designedto investigate the Galaxy's structure and evolution, Hβ photometryis being made for about 9000 stars. As a by-product, supplementary uvbyphotometry has been made. The results are presented in a cataloguecontaining 6924 uvby observations of 6190 stars, all south ofδ=+38deg. The overall internal rms errors of one observation(transformed to the standard system) of a program star in the interval6.5
| Analyses of archival data for cool dwarfs. 2: A catalog of temperatures
A calibration presented in a previous paper is used in this paper toderive temperatures for FGK stars near the main sequence. Thecalibration is checked against published counterparts, and it is foundthat previous calibrations have not established K-dwarf temperatures inparticular beyond reasonable doubt. The database assembled to derive thetemperatures is described, and the problems posed by close binaries areevaluated. The newly derived temperatures are used to check a line-depthratio proposed as a thermometer by Gray and Johanson (1991, PASP, 103,439), and it is found that the ratio is metallicity-sensitive.Temperatures are given for a total of 417 stars.
| Proper motions in the southern ESO areas 207, 439, and 440
Proper motion stars have been identified from red IIIaF EuropeanSouthern Observatory (ESO) Schmidt plates. This calalog includes starsfound in ESO Areas 207, 439, and 440 having mu greater than or equal to0.1 sec/yr. Finding charts for stars with mu greater than or equal to0.25 sec/yr are provided.
| 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.
| Metal-poor subdwarfs and early galactic nucleosynthesis
Observations of more than 20 metal-poor subdwarfs are presented,discussing the spectroscopic abundance analyses based on high-reolutionspectra and scaled solar model atmospheres. Many of the stars are shownto be more evolved than can be reconciled with reasonable time scalesbased on standard theory of stellar evolution, suggesting that the postmain sequence evolution of cool metal-poor stars is influenced by anenhanced O/Fe ratio compared with a standard solar mixture. Radialvelocities are given for 60 metal-poor stars, 25 percent of which aresuspected to be velocity variable. The kinematic properties of severalspecific stars are discussed. The abundance ratios Mg/Fe, Ca/Fe, Ti/Fe,Al/Fe, and Mn/Fe as a function of the Fe abundance itself indicate thatthese elements probably have not been produced in purely explosivenucleosynthesis. It is suggested that a considerable fraction of theisotopes must have been synthesized during preceding hydrostatic burningphases.
| Metallarme Subdwarfs der Spektraltypen F und G
Not Available
| Kinematical and orbital properties for selected southern high-velocity stars
Using the model of the Galaxy presented by Eggen, Lynden-Bell, andSandage (1962), plane galactic orbits have been calculated for severalsouthern high-velocity stars which possess parallax, proper motion, andradial velocity data. Extensive lists of both raw and computed data forthese stars are included. Published values of U-B and B-V for some ofthese stars were used in plots of each of the orbital parameters versusU-B, B-V, or the ultraviolet excess. Also, a comparison is made betweenthe H-R diagrams for the southern high-velocity star group and that ofM3, a globular cluster, and again for M67, an old open cluster. Thehigh-velocity star group is found to resemble an old open cluster morethan a globular cluster.
| Radial velocities and three-colour photometry of 166 southern stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1965MNRAS.131...95P&db_key=AST
|
Yeni bir Makale Öner
Ýlgili Baðlantýlar
Yeni Bir Baðlantý Öner
sonraki gruplarýn üyesi:
|
Gözlemler ve gökölçümü verileri
| Takýmyýldýz: | Karina |
| Sað Açýklýk: | 06h57m45.44s |
| Yükselim: | -52°38'54.5" |
| Görünürdeki Parlaklýk: | 6.92 |
| Uzaklýk: | 36.523 parsek |
| özdevim Sað Açýklýk: | -10.6 |
| özdevim Yükselim: | -372.8 |
| B-T magnitude: | 7.455 |
| V-T magnitude: | 6.965 |
Kataloglar ve belirtme:
|
INHABITED SKY
