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A catalog of rotational and radial velocities for evolved stars. IV. Metal-poor stars^
Aims.The present paper describes the first results of an observationalprogram intended to refine and extend the existing v sin i measurementsof metal-poor stars, with an emphasis on field evolved stars.Methods: .The survey was carried out with the FEROS and CORALIEspectrometers. For the v sin i measurements, obtained from spectralsynthesis, we estimate an uncertainty of about 2.0 km s-1. Results: .Precise rotational velocities v sin i are presented for alarge sample of 100 metal-poor stars, most of them evolving off themain-sequence. For the large majority of the stars composing the presentsample, rotational velocities have been measured for the first time.
| Estimation of Carbon Abundances in Metal-Poor Stars. I. Application to the Strong G-Band Stars of Beers, Preston, and Shectman
We develop and test a method for the estimation of metallicities([Fe/H]) and carbon abundance ratios ([C/Fe]) for carbon-enhancedmetal-poor (CEMP) stars based on the application of artificial neuralnetworks, regressions, and synthesis models to medium-resolution (1-2Å) spectra and J-K colors. We calibrate this method by comparisonwith metallicities and carbon abundance determinations for 118 starswith available high-resolution analyses reported in the recentliterature. The neural network and regression approaches make use of apreviously defined set of line-strength indices quantifying the strengthof the Ca II K line and the CH G band, in conjunction with J-K colorsfrom the Two Micron All Sky Survey Point Source Catalog. The use ofnear-IR colors, as opposed to broadband B-V colors, is required becauseof the potentially large affect of strong molecular carbon bands onbluer color indices. We also explore the practicality of obtainingestimates of carbon abundances for metal-poor stars from the spectralinformation alone, i.e., without the additional information provided byphotometry, as many future samples of CEMP stars may lack such data. Wefind that although photometric information is required for theestimation of [Fe/H], it provides little improvement in our derivedestimates of [C/Fe], and hence, estimates of carbon-to-iron ratios basedsolely on line indices appear sufficiently accurate for most purposes.Although we find that the spectral synthesis approach yields the mostaccurate estimates of [C/Fe], in particular for the stars with thestrongest molecular bands, it is only marginally better than is obtainedfrom the line index approaches. Using these methods we are able toreproduce the previously measured [Fe/H] and [C/Fe] determinations withan accuracy of ~0.25 dex for stars in the metallicity interval-5.5<=[Fe/H]<=-1.0 and with 0.2<=(J-K)0<=0.8. Athigher metallicity, the Ca II K line begins to saturate, especially forthe cool stars in our program, and hence, this approach is not useful insome cases. As a first application, we estimate the abundances of [Fe/H]and [C/Fe] for the 56 stars identified as possibly carbon-rich, relativeto stars of similar metal abundance, in the sample of ``strong G-band''stars discussed by Beers, Preston, and Shectman.
| 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.
| Comparing Deep Mixing in Globular Cluster and Halo Field Giants: Carbon Abundance Data from the Literature
The behavior of carbon abundance as a function of luminosity is used tocompare the rates of deep mixing within red giants of four globularclusters and the Galactic halo field population. Measurements of [C/Fe]for the clusters M92, NGC 6397, M3, and M13 have been compiled from theliterature, together with the Gratton et al. data for halo field stars.Plots of [C/Fe] versus absolute visual magnitude show that forMV<+1.6 the rate of decline of carbon abundance withincreasing luminosity on the red giant branch isd[C/Fe]/dMV~0.22+/-0.03 among the field stars, as well as inM92, NGC 6397, and M3. Among giants fainter than MV=+1.6 thevariation of [C/Fe] with absolute magnitude is much less. The dataindicate that the rate at which deep mixing introduces carbon-depletedmaterial into the convective envelopes of field halo stars during theupper red giant branch phase of evolution is similar to that of manyglobular cluster giants. The notable exception appears to be M13, inwhich stars exhibit deep mixing at a greater rate; this may account forthe high incidence of very low oxygen abundances among the most luminousgiants in M13 in comparison to M3.
| Kinematics of Metal-poor Stars in the Galaxy. II. Proper Motions for a Large Nonkinematically Selected Sample
We present a revised catalog of 2106 Galactic stars, selected withoutkinematic bias and with available radial velocities, distance estimates,and metal abundances in the range -4.0<=[Fe/H]<=0.0. This updateof the 1995 Beers & Sommer-Larsen catalog includes newly derivedhomogeneous photometric distance estimates, revised radial velocitiesfor a number of stars with recently obtained high-resolution spectra,and refined metallicities for stars originally identified in the HKobjective-prism survey (which account for nearly half of the catalog)based on a recent recalibration. A subset of 1258 stars in this cataloghave available proper motions based on measurements obtained with theHipparcos astrometry satellite or taken from the updated AstrographicCatalogue (second epoch positions from either the Hubble Space TelescopeGuide Star Catalog or the Tycho Catalogue), the Yale/San Juan SouthernProper Motion Catalog 2.0, and the Lick Northern Proper Motion Catalog.Our present catalog includes 388 RR Lyrae variables (182 of which arenewly added), 38 variables of other types, and 1680 nonvariables, withdistances in the range 0.1 to 40 kpc.
| Abundances of light elements in metal-poor stars. III. Data analysis and results
We present the results of the analysis of an extensive set of new andliterature high quality data concerning Fe, C, N, O, Na, and Mg. Thisanalysis exploited the T_eff scale determined in Gratton et al. (1996a),and the non-LTE abundance corrections computed in Gratton et al.(1999a). Results obtained with various abundance indices are discussedand compared. Detailed comparison with models of galactic chemicalevolution will be presented in future papers of this series. Our non-LTEanalysis yields the same O abundances from both permitted and forbiddenlines for stars with T_eff >4600 K, in agreement with King (1993),but not with other studies using a lower T_eff -scale for subdwarfs.However, we obtain slightly smaller O abundances for the most luminousmetal-poor field stars than for fainter stars of similar metallicities,an effect attributed to inadequacies of the adopted model atmospheres(Kurucz 1992, with overshooting) for cool stars. We find a nearlyconstant O overundance in metal-poor stars ([Fe/H]<-0.8), at a meanvalue of 0.46+/- 0.02 dex (sigma =0.12, 32 stars), with only a gentleslope with [Fe/H] ( ~ -0.1); this result is different from the steeperslope recently obtained using OH band in the near UV. If only bonafideunmixed stars are considered, C abundances scale with Fe ones (i.e.[C/Fe]~ 0) down to [Fe/H] ~ -2.5. Due to our adoption of a differentT_eff scale, we do not confirm the slight C excess in the most metalpoor disk dwarfs (-0.8<[Fe/H]<-0.4) found in previousinvestigations. Na abundances scale as Fe ones in the high metallicityregime, while metal-poor stars present a Na underabundance. None of thefield stars analyzed belong to the group of O-poor and Na-rich starsobserved in globular clusters. Na is deficient with respect to Mg inhalo and thick disk stars; within these populations, Na deficiency maybe a slow function of [Mg/H]. Solar [Na/Mg] ratios are obtained for thindisk stars. Tables~ 2 to 9 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strabg.fr/Abstract.html
| Revised Strömgren metallicity calibration for red giants
A new calibration of the Strömgren (b-y),m_1 diagram in terms ofiron abundance of red giants is presented. This calibration is based ona homogeneous sample of giants in the globular clusters omega Centauri,M 22, and M 55 as well as field giants from the list of Anthony-Twarog& Twarog (\cite{anth98}). Towards high metallicities, the newcalibration is connected to a previous calibration by Grebel &Richtler (\cite{greb92}), which was unsatisfactory for iron abudanceslower than -1.0 dex. The revised calibration is valid for CN-weak/normalred giants in the abundance range of -2.0 <[Fe/H]< 0.0 dex, and acolor range of 0.5 < (b-y) < 1.1 mag. As shown for red giants inomega Centauri, CN-weak stars with Strömgren metallicities higherthan -1.0 dex cannot be distinguished in the (b-y),m_1 diagram fromstars with lower iron abundances but higher CN band strengths. Based ondata collected at the European Southern Observatory, La Silla, Chile
| Mixing along the red giant branch in metal-poor field stars
We have determined Li, C, N, O, Na, and Fe abundances, and12C/13C isotopic ratios for a sample of 62 fieldmetal-poor stars in the metallicity range -2<=[Fe/H]<= -1. Starswere selected in order to have accurate luminosity estimates from theliterature, so that evolutionary phases could be clearly determined foreach star. We further enlarged this dataset by adding 43 more starshaving accurate abundances for some of these elements and similarly welldefined luminosities from the literature. This large sample was used toshow that (small mass) lower-RGB stars (i.e. stars brighter than thefirst dredge-up luminosity and fainter than that of the RGB bump) haveabundances of light elements in agreement with predictions fromclassical evolutionary models: only marginal changes occur for CNOelements, while dilution within the convective envelope causes thesurface Li abundance to decrease by a factor of ~ 20. A second, distinctmixing episode occurs in most (perhaps all) small mass metal-poor starsjust after the RGB bump, when the molecular weight barrier left by themaximum inward penetration of the convective shell is canceled by theoutward expansion of the H-burning shell, in agreement with recenttheoretical predictions. In field stars, this second mixing episode onlyreaches regions of incomplete CNO burning: it causes a depletion of thesurface 12C abundance by about a factor of 2.5, and acorresponding increase in the N abundance by about a factor of 4. The12C/13C is lowered to about 6 to 10 (close to butdistinctly higher than the equilibrium value of 3.5), while practicallyall remaining Li is burnt. However an O-Na anti-correlation such astypically observed amongst globular cluster stars, is not present infield stars. None of the 29 field stars more evolved than the RGB bump(including 8 RHB stars) shows any sign of an O depletion or Naenhancement. This means that the second mixing episode is not deepenough to reach regions were ON-burning occurs in field stars. Based inpart on observations made at the ESO La Silla ObservatoryTables 1, 2, 3, 5 and 6 are available in electronic form only at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Abundances of metal-weak thick-disc candidates
High-resolution spectra of five candidate metal-weak thick-disc starssuggested by Beers & Sommer-Larsen are analysed to determine theirchemical abundances. The low abundance of all the objects has beenconfirmed, with metallicity reaching [Fe/H]=-2.9. However, for threeobjects the astrometric data from the Hipparcos catalogue suggest theyare true halo members. The remaining two, for which proper-motion dataare not available, may have disc-like kinematics. It is therefore clearthat it is useful to address properties of putative metal-weakthick-disc stars only if they possess full kinematic data. For CS22894-19 an abundance pattern similar to those of typical halo stars isfound, suggesting that chemical composition is not a useful discriminantbetween thick-disc and halo stars. CS 29529-12 is found to be C-enhancedwith [C/Fe]=+1.0 other chemical peculiarities involve the s-processelements: [Sr/Fe]=-0.65 and [Ba/Fe]=+0.62, leading to a high [Ba/Sr],considerably larger than that found in more metal-rich carbon-richstars, but similar to those in LP 706-7 and LP 625-44, discussed byNorris et al. Hipparcos data have been used to calculate the spacevelocities of 25 candidate metal-weak thick-disc stars, thus allowing usto identify three bona fide members, which support the existence of ametal-poor tail of the thick disc, at variance with a claim to thecontrary by Ryan & Lambert.
| A Model for Calculating the Abundances of Neutron-Capture Elements in Metal-poor Stars
Several previous studies on the abundances of neutron-capture elementshave indicated that, for most metal-poor stars, the observed abundancesof the heavy elements cannot be matched by only one neutron-captureprocess, either the solar system r-process or the solar s-processabundances. However, the observed abundances can be well matched by thecombined contributions from both of these solar system neutron-captureprocesses in certain proportions. So it is necessary to determine therelative contributions from the individual neutron-capture processes tothe abundances of the heavy elements in metal-poor stars. In this paperwe suggest a new concept of component coefficients to describe therelative contributions of the individual n-processes to the synthesis ofthe heavy elements and we set up a model to calculate the componentcoefficients and the abundances of heavy elements in metal-poor starswith different metallicities. With this model, we then calculate thecomponent coefficients and the abundances of the heavy elements in 18metal-poor stars. We find that, for most sample stars, the modelcalculations are basically in agreement with the observations of theheavy elemental abundances within the error limits and the fits of themodel predictions are much better for the heaviest elements than for thelighter elements, specifically for Sr, Y, and Zr. We discuss this resultand give a possible explanation for it. Moreover, we also discuss thephysical meanings of the component coefficients.
| 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.
| Ca II H and K Photometry on the UVBY System. III. The Metallicity Calibration for the Red Giants
New photometry on the uvby Ca system is presented for over 300 stars.When combined with previous data, the sample is used to calibrate themetallicity dependence of the hk index for cooler, evolved stars. Themetallicity scale is based upon the standardized merger of spectroscopicabundances from 38 studies since 1983, providing an overlap of 122evolved stars with the photometric catalog. The hk index producesreliable abundances for stars in the [Fe/H] range from -0.8 to -3.4,losing sensitivity among cooler stars due to saturation effects athigher [Fe/H], as expected.
| Early evolution of the Galactic halo revealed from Hipparcos observations of metal-poor stars
The kinematics of 122 red giant and 124 RR Lyrae stars in the solarneighborhood are studied using accurate measurements of their propermotions obtained by the Hipparcos astrometry satellite, combined withtheir published photometric distances, metal abundances, and radialvelocities. A majority of these sample stars have metal abundances of(Fe/H) = -1 or less and thus represent the old stellar populations inthe Galaxy. The halo component, with (Fe/H) = -1.6 or less, ischaracterized by a lack of systemic rotation and a radially elongatedvelocity ellipsoid. About 16 percent of such metal-poor stars have loworbital eccentricities, and we see no evidence of a correlation between(Fe/H) and e. Based on the model for the e-distribution of orbits, weshow that this fraction of low-e stars for (Fe/H) = -1.6 or less isexplained by the halo component alone, without introducing the extradisk component claimed by recent workers. This is also supported by theabsence of a significant change in the e-distribution with height fromthe Galactic plane. In the intermediate-metallicity range, we find thatstars with disklike kinematics have only modest effects on thedistributions of rotational velocities and e for the sample at absolutevalue of z less than 1 kpc. This disk component appears to constituteonly 10 percent for (Fe/H) between -1.6 and -1 and 20 percent for (Fe/H)between -1.4 and -1.
| 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
| Abundances of light elements in metal-poor stars. I. Atmospheric parameters and a new T_eff_ scale
We present atmospheric parameters for about 300 stars of differentchemical composition, whose spectra will be used to study the galacticenrichment of Fe and light elements. These parameters were derived usingan homogeneous iterative procedure, which considers new calibrations ofcolour-T_eff_ relations for F, G and K-type stars based on Infrared FluxMethod (IRFM) and interferometric diameters for population I stars, andthe Kurucz (1992) model atmospheres. We found that these calibrationsyield a self-consistent set of atmospheric parameters forT_eff_>4400K, representing a clear improvement over results obtainedwith older model atmospheres. Using this T_eff_ -scale and Feequilibrium of ionization, we obtained very low gravities (implyingluminosities incompatible with that expected for RGB stars) formetal-poor stars cooler than 4400K; this might be due either to amoderate Fe overionization (expected from statistical equilibriumcalculations) or to inadequacy of Kurucz models to describe theatmospheres of very cool giants. Our T_eff_ scale is compared with otherscales recently used for metal-poor stars; it agrees well with thoseobtained using Kurucz (1992) models, but it gives much larger T_eff_'sthan those obtained using OSMARCS models (Edvardsson et al. 1993). Thisdifference is attributed to the different treatment of convection in thetwo sets of models. For the Sun, the Kurucz (1992) model appears to bepreferable to the OSMARCS ones because it better predicts the solar limbdarkening; furthermore, we find that our photometric T_eff_ 's formetal-poor stars agree well with both direct estimates based on theIRFM, and with T_eff_'s derived from Hα wings when using Kuruczmodels.
| Abundance of barium in metal poor stars.
Abundance determination of barium in a sample of metal poor stars hasbeen performed using high resolution, high S/N ratio spectra. These datahave been combined with recent abundance determinations of europium. Aplot of [Eu/H] as a function [Ba/H] shows a tight correlation with asingle slope different from 45deg. The interpretation of these data doesnot seem to require the hypothesis of an r-process synthesis of bariumin the early galactic history.
| Ca II H and K Filter Photometry on the UVBY System. II. The Catalog of Observations
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....109.2828T&db_key=AST
| Kinematics of metal-poor stars in the galaxy
We discuss the kinematic properties of a sample of 1936 Galactic stars,selected without kinematic bias, and with abundances (Fe/H) is less thanor equal to -0.6. The stars selected for this study all have measuredradial velocities, and the majority have abundances determined fromspectroscopic or narrow-/intermediate-band photometric techniques. Incontrast to previous examinations of the kinematics of the metal-poorstars in the Galaxy, our sample contains large numbers of stars that arelocated at distances in excess of 1 kpc from the Galactic plane. Thus, amuch clearer picture of the nature of the metal-deficient populations inthe Galaxy can now be drawn.
| Abundances of neutron-capture elements in metal-poor stars
We use a large set of high S/N, high resolution spectra of 19 stars with-2.8<[Fe/H]<0 to study the abundances of neutron-rich elements inmetal-poor stars. Basic data (atmospheric parameters, iron abundances,abundance indices, atomic and line parameters) are carefully examinedboth for the Sun and for the program stars, and extensive use is made ofcomparisons with synthetic spectra. New analyses of solar abundances ofSr, La, and Ce are presented; deduced abundances agree well withmeteoritic results. Our stellar abundances are briefly compared withnucleosynthesis predictions. The main results are: 1. Those elementswhose solar abundances are mainly attributed to the s-process (e.g. Baand La) are overdeficient in extremely metal-poor stars ([Fe/H]<-2)with respect to those elements whose solar abundances are mainlyattributed to the r-process (e.g. Eu). We did not find any clearevidence for a plateau in abundance ratios like [Ba/Eu] at these lowvalues of [Fe/H]. 2. Eu itself begins to decline (with respect either toFe or Mg) in the most metal-poor stars, with perhaps a sharp drop instars with [Fe/H]<-2.5. If the r-process mainly occurs in SNexplosions of massive stars, then the abundances of its products in theejecta are a function of initial stellar mass and/or metallicity. 3. Theabundance pattern of neutron-capture elements in metal-poor stars showclear differences with respect to scaled solar-system r-processnucleosynthesis predictions; e.g. there is a relative excess of Ba(attributed mainly to the s-process). This pattern may be explained ifthe contribution of the s-process to the solar abundances of heavyelements is overestimated, or the production of heavy elements throughthe r-process was different when [Fe/H] was much lower than the presentvalue, or there was an early onset of the contribution by the maincomponent of the s-process in the Galactic chemical evolution.
| An Abundance Calibration for DDO Photometry of Population-II G and K Giants
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1994MNRAS.268..733C&db_key=AST
| Nucleosynthese : le probleme des elements a processus-r.
Not Available
| On the Galactic Age Problem - Determination of the Th/eu Ratio in Halo Stars
Abstract image available at:http://adsabs.harvard.edu/abs/1993A&A...274..821F
| Spectroscopy of the CA II K line of metal-poor field red giants. I - Southern Hemisphere observations
Spectra of the Ca II K line have been obtained for a sample of fieldmetal-poor red giants. Strong chromospheric emission is found to bequite common among such giants of absolute magnitude brighter than M(v)about -0.3. The behavior of the violet/red asymmetry of the emissionline profile shows no significant difference with that observed amongPopulation I red giants, suggesting that the onset of material outflowis independent of metallicity. The Ca II emission is observed amonggiants more than one magnitude fainter than those which exhibit emissionin the wings of the H-alpha line. One possible interpretation of thisresult is that the transient phenomenon associated with the variableH-alpha emission does not become established until a Population II giantattains luminosities considerably greater than those at whichwell-developed chromospheres are achieved.
| 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.
| Abundances of elements of the Fe-group in metal-poor stars
The paper presents results of an analysis of the abundances of elementsof the Fe group and Si in 19 field stars with Fe/H ranging from -2.7 to-0.2. The hyperfine structure is fully considered for lines of the oddelements. The abundances in metal-poor stars are compared with thepredictions of nucleosynthesis theories for Fe group elements. Apromising agreement with recent calculations for production of theseelements by type II SNe is obtained.
| Equivalent widths for Fe-group lines in field and cluster metal poor stars
Abundances of Fe-group elements in field and cluster metal poor starshave been presented in Gratton and Sneden (1990). Presented here is atabulation of the equivalent widths used in that paper. Errors in theseequivalent widths are + or - 2 mA for field stars (observed at aresolution of 50,000 and S/N of 150 or less), and + or - 10 mA incluster giants (observed at a resolution of 20,000 and S/N of 100 orless). These errors are mainly due to uncertainties (about 1-1.5) in thelocation of the continuum level.
| Armchair cartography - A map of the Galactic halo based on observations of local, metal-poor stars
The velocity distribution of metal-poor halo stars in the solarneighborhood is studied to extract data on the global spatial andkinematic properties of the Galactic stellar halo. A global model of thesolar neighborhood stars is constructed from observed positions andthree-dimensional velocity of local, metal-poor halo stars in terms of adiscrete sum of orbits. The characteristics of the reconstructed haloare examined and used to study the evolution of the halo subsystems.
| Light element and NI abundance in field disk and halo stars
The results of a new, extensive abundance survey of the elements Na, Mg,Al, Si, and K in halo and disk dwarfs and giants is reported. Abundancesfor metal-poor field giants agree with those derived for field dwarfs.Observed alpha elements are overabundant with respect to iron in halostars by 0.4 + or - 0.1 dex for Si, 0.3 + or - 0.1 dex for Mg, 0.2 + or- 0.1 dex for Ca, and 0.2 + or - 0.1 dex for Ti. Na and Al areunderabundant in halo stars with respect to alpha elements by about 0.5+ or - 0.1 and 0.3 + or - 0.1 dex, respectively. Na and Al abundancesare correlated; Ni is slightly underabundant in halo stars.
| Equivalent widths for field halo and disk stars
Abstract image available at:http://adsabs.harvard.edu/abs/1987A&AS...68..193G
| The forbidden O/Fe ratio in metal-poor late-type stars
The oxygen-to-iron ratio has been derived in 18 late-type stars ofdifferent evolutionary status and chemical composition. Oxygen has beenfound to be slightly overabundant in metal-poor stars. This result issimilar to that obtained in previous studies. The presently derivedabundances are briefly compared with theoretical models of galacticchemical evolution.
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Группы:
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Наблюдательные данные и астрометрия
| Созвездие: | Волк |
| Прямое восхождение: | 15h22m17.94s |
| Склонение: | -53°14'15.3" |
| Видимая звёздная величина: | 7.639 |
| Расстояние: | 925.926 парсек |
| Собственное движение RA: | -28.2 |
| Собственное движение Dec: | -69.1 |
| B-T magnitude: | 9.104 |
| V-T magnitude: | 7.76 |
Каталоги и обозначения:
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