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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
| Strömgren Photometry of Galactic Globular Clusters. I. New Calibrations of the Metallicity Index
We present a new calibration of the Strömgren metallicity indexm1 using red giant (RG) stars in four globular clusters (GCs:M92, M13, NGC 1851, 47 Tuc) with metallicity ranging from -2.2 to -0.7,marginally affected by reddening [E(B-V)<=0.04] and with accurate(u,v,b,y) photometry. The main difference between the newmetallicity-index-color (MIC) relations and similar relations availablein the literature is that we have adopted the u-y and v-y colors insteadof b-y. These colors present a stronger sensitivity to effectivetemperature, and the MIC relations show a linear slope. The differencebetween photometric estimates and spectroscopic measurements for RGs inM71, NGC 288, NGC 362, NGC 6397, and NGC 6752 is 0.04+/-0.03 dex(σ=0.11 dex). We also apply the new MIC relations to 85 field RGswith metallicity ranging from -2.4 to -0.5 and accurate reddeningestimates. We find that the difference between photometric estimates andspectroscopic measurements is -0.14+/-0.01 dex (σ=0.17 dex). Wealso provide two sets of MIC relations based on evolutionary models thathave been transformed into the observational plane by adopting eithersemiempirical or theoretical color-temperature relations. We apply thesemiempirical relations to the nine GCs and find that the differencebetween photometric and spectroscopic metallicities is 0.04+/-0.03 dex(σ=0.10 dex). A similar agreement is found for the sample of fieldRGs, with a difference of -0.09+/-0.03 dex (with σ=0.19 dex). Thedifference between metallicity estimates based on theoretical relationsand spectroscopic measurements is -0.11+/-0.03 dex (σ=0.14 dex)for the nine GCs and -0.24+/-0.03 dex (σ=0.15 dex) for the fieldRGs. Current evidence indicates that new MIC relations providemetallicities with an intrinsic accuracy better than 0.2 dex.Based in part on observations collected with the 1.54 m Danish Telescopeoperated at ESO (La Silla, Chile) and with the Nordic Optical Telescope(NOT) operated at La Palma (Spain).
| Chemical Abundance Analysis of the Extremely Metal-poor Star HE 1300+0157
We present a detailed chemical abundance analysis of HE 1300+0157, asubgiant with [Fe/H]=-3.9. From a high-resolution, high-S/N Subaru HDSspectrum we find the star to be enriched in C ([C/Fe]1D~+1.4)and O ([O/Fe]1D~+1.8). With the exception of these species,HE 1300+0157 exhibits an elemental abundance pattern similar to thatfound in many other very and extremely metal-poor stars. The Liabundance is lower than the Spite plateau value, in agreement withexpectation for its evolutionary status. Of particular interest, noneutron-capture elements are detected in HE 1300+0157. This type ofabundance pattern has been found by recent studies in several othermetal-poor giants. We suggest that HE 1300+0157 is an unevolved exampleof this group of stars, which exhibit high C abundances together withlow (or absent) abundances of neutron-capture elements (CEMP-no).Several potential enrichment scenarios are presented. The nondetectionof neutron-capture elements including Sr, Ba, and Pb suggests that thecarbon excess observed in HE 1300+0157 is not due to mass transferacross a binary system. Such a scenario is applied to carbon-richobjects with excesses of s-process elements. The normal observed Liabundance supports this interpretation. Most likely, the high levels ofC and O were produced prior to the birth of this star. It remainsunclear whether a single faint SN is responsible for its overallchemical pattern, or whether one requires a superposition of yields froma massive Population III object and a hypernova. These scenarios provideimportant information on the C production in the early universe and onthe formation of C-rich stars in the early Galaxy.Based on data collected at the Subaru Telescope, which is operated bythe National Astronomical Observatory of Japan.
| Stellar Chemical Signatures and Hierarchical Galaxy Formation
To compare the chemistries of stars in the Milky Way dwarf spheroidal(dSph) satellite galaxies with stars in the Galaxy, we have compiled alarge sample of Galactic stellar abundances from the literature. Whenkinematic information is available, we have assigned the stars tostandard Galactic components through Bayesian classification based onGaussian velocity ellipsoids. As found in previous studies, the[α/Fe] ratios of most stars in the dSph galaxies are generallylower than similar metallicity Galactic stars in this extended sample.Our kinematically selected stars confirm this for the Galactic halo,thin-disk, and thick-disk components. There is marginal overlap in thelow [α/Fe] ratios between dSph stars and Galactic halo stars onextreme retrograde orbits (V<-420 km s-1), but this is notsupported by other element ratios. Other element ratios compared in thispaper include r- and s-process abundances, where we find a significantoffset in the [Y/Fe] ratios, which results in a large overabundance in[Ba/Y] in most dSph stars compared with Galactic stars. Thus, thechemical signatures of most of the dSph stars are distinct from thestars in each of the kinematic components of the Galaxy. This resultrules out continuous merging of low-mass galaxies similar to these dSphsatellites during the formation of the Galaxy. However, we do not ruleout very early merging of low-mass dwarf galaxies, since up to one-halfof the most metal-poor stars ([Fe/H]<=-1.8) have chemistries that arein fair agreement with Galactic halo stars. We also do not rule outmerging with higher mass galaxies, although we note that the LMC and theremnants of the Sgr dwarf galaxy are also chemically distinct from themajority of the Galactic halo stars. Formation of the Galaxy's thickdisk by heating of an old thin disk during a merger is also not ruledout; however, the Galaxy's thick disk itself cannot be comprised of theremnants from a low-mass (dSph) dwarf galaxy, nor of a high-mass dwarfgalaxy like the LMC or Sgr, because of differences in chemistry.The new and independent environments offered by the dSph galaxies alsoallow us to examine fundamental assumptions related to thenucleosynthesis of the elements. The metal-poor stars ([Fe/H]<=-1.8)in the dSph galaxies appear to have lower [Ca/Fe] and [Ti/Fe] than[Mg/Fe] ratios, unlike similar metallicity stars in the Galaxy.Predictions from the α-process (α-rich freeze-out) would beconsistent with this result if there have been a lack of hypernovae indSph galaxies. The α-process could also be responsible for thevery low Y abundances in the metal-poor stars in dSph's; since [La/Eu](and possibly [Ba/Eu]) are consistent with pure r-process results, thelow [Y/Eu] suggests a separate r-process site for this light(first-peak) r-process element. We also discuss SNe II rates and yieldsas other alternatives, however. In stars with higher metallicities([Fe/H]>=-1.8), contributions from the s-process are expected; [(Y,La, and Ba)/Eu] all rise as expected, and yet [Ba/Y] is still muchhigher in the dSph stars than similar metallicity Galactic stars. Thisresult is consistent with s-process contributions from lower metallicityAGB stars in dSph galaxies, and is in good agreement with the slowerchemical evolution expected in the low-mass dSph galaxies relative tothe Galaxy, such that the build-up of metals occurs over much longertimescales. Future investigations of nucleosynthetic constraints (aswell as galaxy formation and evolution) will require an examination ofmany stars within individual dwarf galaxies.Finally, the Na-Ni trend reported in 1997 by Nissen & Schuster isconfirmed in Galactic halo stars, but we discuss this in terms of thegeneral nucleosynthesis of neutron-rich elements. We do not confirm thatthe Na-Ni trend is related to the accretion of dSph galaxies in theGalactic halo.
| 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
| A grid of synthetic spectra and indices Fe5270, Fe5335, Mgb and Mg2 as a function of stellar parameters and [alpha/Fe]
We have computed a grid of synthetic spectra in the wavelength rangelambda lambda 4600-5600 Å using revised model atmospheres, for arange of atmospheric parameters and values of [alpha -elements/Fe] = 0.0and +0.4. The Lick indices Fe5270, Fe5335, Mgb and Mg2 aremeasured on the grid spectra for FWHM = 2 to 8.3 Å. Relationsbetween the indices Fe5270, Fe5335 and Mg2 and the stellarparameters effective temperature Teff, log ; g, [Fe/H] and[alpha /Fe], valid in the range 4000 <= Teff <= 7000 K,are presented. These fitting functions are given for FWHM = 3.5 and 8.3Å. The indices were also measured for a list of 97 reference starswith well-known stellar parameters observed at ESO and OHP, and theseare compared to the computed indices. Finally, a comparison of theindices measured on the observed spectra and those derived from thefitting functions based on synthetic spectra is presented.Observations collected at the European Southern Observatory (ESO), LaSilla, Chile and at the Observatoire de Haute Provence (OHP), St-Michel,France.All Tables of Appendices A and B are only available in electronic format the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/cgi-bin/qcat?/A+A/404/661
| Three-dimensional Spectral Classification of Low-Metallicity Stars Using Artificial Neural Networks
We explore the application of artificial neural networks (ANNs) for theestimation of atmospheric parameters (Teff, logg, and [Fe/H])for Galactic F- and G-type stars. The ANNs are fed withmedium-resolution (Δλ~1-2 Å) non-flux-calibratedspectroscopic observations. From a sample of 279 stars with previoushigh-resolution determinations of metallicity and a set of (external)estimates of temperature and surface gravity, our ANNs are able topredict Teff with an accuracy ofσ(Teff)=135-150 K over the range4250<=Teff<=6500 K, logg with an accuracy ofσ(logg)=0.25-0.30 dex over the range 1.0<=logg<=5.0 dex, and[Fe/H] with an accuracy σ([Fe/H])=0.15-0.20 dex over the range-4.0<=[Fe/H]<=0.3. Such accuracies are competitive with theresults obtained by fine analysis of high-resolution spectra. It isnoteworthy that the ANNs are able to obtain these results withoutconsideration of photometric information for these stars. We have alsoexplored the impact of the signal-to-noise ratio (S/N) on the behaviorof ANNs and conclude that, when analyzed with ANNs trained on spectra ofcommensurate S/N, it is possible to extract physical parameter estimatesof similar accuracy with stellar spectra having S/N as low as 13. Takentogether, these results indicate that the ANN approach should be ofprimary importance for use in present and future large-scalespectroscopic surveys.
| Estimation of Stellar Metal Abundance. II. A Recalibration of the Ca II K Technique, and the Autocorrelation Function Method
We have recalibrated a method for the estimation of stellar metalabundance, parameterized as [Fe/H], based on medium-resolution (1-2Å) optical spectra (the majority of which cover the wavelengthrange 3700-4500 Å). The equivalent width of the Ca II K line (3933Å) as a function of [Fe/H] and broadband B-V color, as predictedfrom spectrum synthesis and model atmosphere calculations, is comparedwith observations of 551 stars with high-resolution abundances availablefrom the literature (a sevenfold increase in the number of calibrationstars that were previously available). A second method, based on theFourier autocorrelation function technique first described by Ratnatunga& Freeman, is used to provide an independent estimate of [Fe/H], ascalibrated by comparison with 405 standard-star abundances.Metallicities based on a combination of the two techniques for dwarfsand giants in the color range 0.30<=(B-V)_0<=1.2 exhibit anexternal 1 sigma scatter of approximately 0.10-0.20 dex over theabundance range -4.0<=[Fe/H]<=0.5. Particular attention has beengiven to the determination of abundance estimates at the metal-rich endof the calibration, where our previous attempt suffered from aconsiderable zero-point offset. Radial velocities, accurate toapproximately 10 km s^-1, are reported for all 551 calibration stars.
| 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
| Classification of Population II Stars in the Vilnius Photometric System. I. Methods
The methods used for classification of Population II stars in theVilnius photometric system are described. An extensive set of standardswith known astrophysical parameters compiled from the literature sourcesis given. These standard stars are classified in the Vilnius photometricsystem using the methods described. The accuracy of classification isevaluated by a comparison of the astrophysical parameters derived fromthe Vilnius photometric system with those estimated from spectroscopicstudies as well as from photometric data in other systems. For dwarfsand subdwarfs, we find a satisfactory agreement between our reddeningsand those estimated in the uvbyscriptstyle beta system. The standarddeviation of [Fe/H] deter mined in the Vilnius system is about 0.2 dex.The absolute magnitude for dwarfs and subdwarfs is estimated with anaccuracy of scriptstyle <=0.5 mag.
| Reddening estimation for halo red giants using UVBY photometry
Updated uvby observations for a larger sample of metal-deficient redgiants are presented and combined with a select sample of data from theliterature transformed to a common system. Using the reddening maps ofBurstein & Heiles (1982), new absolute magnitudes, distances,metallicities, and reddenings are derived for each star. Themetallicities are determined with a revised calibration of them1, (b-y) diagram based upon comparison to a complilation ofrecent spectrsoscopic abundances transformed to a common system. Thephotometric abundances agree very well with the spectroscopic; thedispersion among the residuals for 58 giants is +/- 0.16 dex. Thedereddened indices are used to show that for red giants with (Fe/H) lessthan -1.5, there is a well-defined relation in the c0,(b-y)0 diagram which exhibits only a weak dependence uponmetallicity. Use of the standard relations allows one to obtainreddening estimates for normal halo field giants and globular clustersin the appropriate metallicity range.
| Stromgren Four-Colour UVBY Photometry of G5-TYPE Hd-Stars Brighter than MV=8.6
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&AS..102...89O&db_key=AST
| 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.
| A Grid of Synthetic Spectra for the Determination of Effective Temperature Gravity and Metallicity of F-Stars G-Stars and K-Stars - Part Two - Application to 41 Stellar Spectra Taken in the Basel Field of SA:141
A grid of synthetic spectra is used to derive the atmospheric parameterstemperature Teff, gravity log g and metallicity [M/H],besides the radial velocity, from low-resolution spectra of 41 stars inthe Basel field SA 141 in the direction of the south galactic pole (l =245°.0, b = -85°.8).The metallicity distribution as a function of distance from the galacticplane is obtained and discussed.
| A grid of synthetic spectra for the determination of effective temperature, gravity and metallicity of F, G, and K stars. I - Description of the method. II - Application to 41 stellar spectra taken in the Basel field of SA 141
Abstract image available at:http://adsabs.harvard.edu/abs/1991A&A...247..108C
| Trends in copper and zinc abundances for disk and halo stars
Results are presented of spectroscopic investigations of the Cu and Znabundances in 40 disk and halo stars. The results confirmed and extendedthe previous findings of Sneden and Crocker (1988). It is shown that theZn abundances closely track the overall metallicities: Zn/M = +0.04 + or- 0.02. However, all metal-poor stars displayed Cu deficiencies, whichappear to vary linearly with metallicity: Cu/M = 0.38(M/H) + 0.15. TheCu-abundance trend in giants of 15 globular clusters is in goodagreement with that of the field stars. The nucleosynthesis implicationsof the obtained results are discussed.
| Subdwarf studies. II - Abundances and kinematics from medium resolution spectra. III - The halo metallicity distribution
Stars previously identified as having UV excesses are observed at 1-Aresolution in the Ca II K-line region. Comparisons of these data withother samples and with Monte Carlo simulations involving a singlecomponent halo have yielded estimates of halo velocity dispersions androtation velocity, corrected for the kinematic biases in the sample. Itis suggested that the data are not consistent with a model in which thehalo formed from star formation in a dissipating, collapsing cloud; theyare, however, reconcilable with the formation of the halo stars bynumerous, independently evolving gas clouds. The metallicitydistribution of a sample of 372 kinematically selected halo stars isthen constructed, with a view to selection effects in the data. Goodagreement is noted between the globular cluster metallicity distributionand a stochastic model with a mean of 10 enrichments/fragment.
| Astrometric and astrophysical discontinuities between the galactic old disk and halo stellar populations
Intermediate band, RI, and DDO photometry of the weak-lined stars in thefirst three volumes of the Michigan catalogs of spectral type arediscussed on the basis of luminosity and heavy element abundance. Theinterface between the old disk (Fe/H greater than -0.8 dex) and halo(Fe/H less than -1.2 dex) populations represents discontinuities in boththe stellar motions and the stellar physics. The CN strengths of bothevolved and unevolved halo stars decrease with decreasing temperature,in a mirror image of the increase with decreasing temperature for thedisk objects. The result for the halo giants has been attributed to deepmixing in the stellar atmospheres but the similar result for unevolveddwarfs indicates a difference in formation rather than in evolutionaryprocess of the two populations.
| Estimation of stellar metal abundance. I - Calibration of the CA II K index
A method for estimating the stellar metal abundances is proposed whichcompares measures of the equivalent width of a single feature inmoderate resolution (1 A) optical spectra of stars, the Ca II K line at3933 A, with models of the predicted line strength as a function of thebroadband B-V color and Fe/H. The approach is capable of providingestimates of stellar metallicity over the range -4.5 to -1.0 with ascatter of about 0.15 dex for dwarfs and giants in the color range0.33-0.85. For cooler stars, with B-V in the range 0.85-1.1, the scattermay be as large as 0.19 dex. The calibration of the Ca II K index withFe/H is discussed, and average radial velocities and abundances arepresented for several galactic globular clusters.
| Abundances in extremely metal-poor stars
Abundances of several elements are derived for 13 extremely metal poorgiants from blue and yellow CCD CASPEC spectra. Internal and externalerrors in the system of equivalent widths are discussed in some detail,as well as the use of strong (often resonance) lines for abundanceanalyses. The authors have found that their equivalent widhts comparewell with literature values, and that once an accurate analysis ofcollisional damping is made, strong lines provide abundances for theprogram stars in agreement with those determined from weak lines. Use ofabsolute and differential analysis is also discussed.: it is found thatan absolute analysis is preferable for the stars under consideration.
| New subdwarfs. VI - Kinematics of 1125 high-proper-motion stars and the collapse of the Galaxy
The UVW velocity components, planar eccentricities, and angular momentaof 878 high-proper-motion stars are determined using the radial-velocitydata of Fouts and Sandage (1986) and compared with chemical abundancesand photometric parallaxes from the UBV photometry of Sandage and Kowal(1986). The results are presented, along with published data on 247additional stars, in extensive tables and graphs and characterized indetail. Two approximately equal components are differentiated: alow-velocity component identified as part of the thick disk described byGilmore and Reid (1983) and a high-velocity halo component. The data arefound to support a model of Galactic collapse (with concomitant spinupand progressive chemical enrichment) which includes a rotating bulge(the thick disk) with kinematic and metallicity properties between thoseof the old thin disk and the halo.
| Population studies. II - Kinematics as a function of abundance and galactocentric position for (Fe/H) of -0.6 or less
A catalog is presented of some 1200 Galactic objects which have radialvelocities and (Fe/H) abundances of -0.6 or less. These data areanalyzed to yield information on the kinematic properties of the olderpopulations of the Galaxy and on the interdependence between kinematicsand abundance. It is found that the kinematics of the availablekinematically selected stars differ from those of the nonkinematicallyselected objects. No evidence is found for any significant difference inthe kinematic properties of the various halo subgroups, nor for anydependence of kinematics on abundance. While the rotation of the halo issmall at about 37 km/s for (Fe/H) of -1.2 or less, it rises quickly forhigher abundances to a value of about 160 km/s at (Fe/H) = 0.6. Objectsin the abundance range -0.9 to -0.6 appear to belong predominantly to apopulation possessing the kinematic characteristics of a thick disk. Theimplications of these findings for the suggestion that globular clustersbelong to the same population as the noncluster objects, for the originof the thick disk, and for the mass of the Galaxy are discussed.
| Population studies. I - The Bidelman-MacConnell 'weak-metal' stars
BRVI and DDO photometry are presented for 309 Bidelman-MacConnell'weak-metal' stars. Radial velocities are calculated for most of thestars having Fe/H abundances of no more than -0.8. The photometricobservations were carried out using the 0.6-meter and 1.0-metertelescopes of the Siding Spring Observatory. Photometric taxonomy wasused to classify the stars as dwarfs, giants, red-horizontal branchstars, and ultraviolet-bright stars, respectively. It is found that 35percent of the stars are giants; 50 percent are dwarfs; and 5 percentbelong to the red-horizontal branch group. The role of selection effectsin investigations of the formation of the Galaxy is discussed on thebasis of the photometric observations and the observational constraintsproposed by Eggen et al. (1962).
| A catalogue of Fe/H determinations, 1984 edition
The present version of the Cayrel de Strobel et al. (1981) catalog ofFe/H abundance ratio determinations contains 1921 values for 1035 stars,which represents an augmentation over the previous publication of 48 and47 percent, respectively. In addition, the literature search conductedis complete up to December, 1983. Stellar metal abundance, effectivetemperature, spectroscopic gravity, spectral type, and photometricindices are covered.
| The halo population G and K subdwarfs
The photometry of G and K subdwarfs is analyzed in order to determinetheir metallicity using a system invented by the Lithuanian Academy ofSciences (the Vilnius method). The Vilnius method permits therecognition of F-G-K subdwarfs in conditions of interstellar reddening.For quantitative interpretation of line strengths, a group of syntheticspectrum calculations were used. A series of diagrams is provided whichillustrates the photometric data.
| Catalogue of Metal-Deficient F-Stars to M-Stars - Part One - Stars Classified Spectroscopically - Supplement One
Not Available
| Status of evolution of F, G, and K field stars contained in the Fe/H abundance ratio catalogue
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1983A&A...119....1C&db_key=AST
| Three-dimensional calssification of F-M type halo stars in the Vilnius photometric system
Not Available
| Stars Named after Astronomers Names
Not Available
| The subdwarf helium abundance and the rotation of the galactic halo
Temperatures, barometric corrections, and metallicities for eightsubdwarfs with good trigonometric parallaxes and 10 Hyades dwarfs areused to determine that subdwarfs lie well below the Hyades in theluminosity-temperature diagram. The subdwarf locus is compared to thetheoretical isochrones of Ciardullo and Demarque to derive a subdwarfhelium mass fraction. The adopted distance callibration is used toinvestigate the kinematics of the subdwarfs. Upon adopting 250 km/s asthe rotational velocity of the local standard of rest about the galacticcenter, several subdwarfs were found to be moving in retrograde orbitswhile others were moving in direct circular orbits exceeding 400 km/s.
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הכנס לינק חדש
משמש של הקבוצה הבאה
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | פסל |
| התרוממות ימנית: | 01h32m19.83s |
| סירוב: | -30°40'51.5" |
| גודל גלוי: | 10.75 |
| תנועה נכונה: | 38.4 |
| תנועה נכונה: | -81.1 |
| B-T magnitude: | 11.516 |
| V-T magnitude: | 10.814 |
קטלוגים וכינוים:
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