תוכן
תמונות
הוסף תמונה שלך
DSS Images Other Images
מאמרים קשורים
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.
| A 2 Micron H2 Spectral Survey of Proto-Planetary Nebulae
We measured 2.1-2.3 μm spectra for a mostly complete sample of knownproto-planetary nebulae (PPNe) at declinations north of -30°. Thisspectral range includes the H2 emission lines 1-0 S(1), 1-0S(0), 2-1 S(1), 2-1 S(2), and 3-2 S(3). We detected H2emission from 16 of the 51 objects in our survey. Twelve of these arenew detections, doubling the number of PPNe with detected H2emission. We find that H2 emission commences at a spectralclass of mid-G in PPNe with bipolar morphologies and optically thickequatorial regions; in fact, all bipolar F-G PPNe with an opticallythick equatorial region have collisionally excited H2emission. Radiative excitation becomes important in PPNe when thecentral star reaches an early B spectral type, just beforephotoionization of the nebula and the commencement of the planetarynebula (PN) phase. Almost all of the PPNe with B central stars showH2 emission, with either a purely radiative or a mixedcollisional plus radiative spectrum. Since H2 emission israre in nonbipolar PNe, the destruction of the H2 in thenonbipolars must be roughly coincident with the photoionization of thenebula. As with H2-emitting PNe, the bipolarH2-emitting PPNe are found at low Galactic latitudes.Optically thin H2-emitting nebulae are not similarlyrestricted to low latitudes. Brγ emission is detected in 15 of thesources, including all those of B spectral type.
| Abundance trends in kinematical groups of the Milky Way's disk
We have compiled a large catalogue of metallicities and abundance ratiosfrom the literature in order to investigate abundance trends of severalalpha and iron peak elements in the thin disk and the thick disk of theGalaxy. The catalogue includes 743 stars with abundances of Fe, O, Mg,Ca, Ti, Si, Na, Ni and Al in the metallicity range -1.30 < [Fe/H]< +0.50. We have checked that systematic differences betweenabundances measured in the different studies were lower than randomerrors before combining them. Accurate distances and proper motions fromHipparcos and radial velocities from several sources have been retreivedfor 639 stars and their velocities (U, V, W) and galactic orbits havebeen computed. Ages of 322 stars have been estimated with a Bayesianmethod of isochrone fitting. Two samples kinematically representative ofthe thin and thick disks have been selected, taking into account theHercules stream which is intermediate in kinematics, but with a probabledynamical origin. Our results show that the two disks are chemicallywell separated, they overlap greatly in metallicity and both showparallel decreasing alpha elements with increasing metallicity, in theinterval -0.80 < [Fe/H] < -0.30. The Mg enhancement with respectto Fe of the thick disk is measured to be 0.14 dex. An even largerenhancement is observed for Al. The thick disk is clearly older than thethin disk with tentative evidence of an AMR over 2-3 Gyr and a hiatus instar formation before the formation of the thin disk. We do not observea vertical gradient in the metallicity of the thick disk. The Herculesstream has properties similar to that of the thin disk, with a widerrange of metallicity. Metal-rich stars assigned to the thick disk andsuper-metal-rich stars assigned to the thin disk appear as outliers inall their properties.
| Lithium abundances of the local thin disc stars
Lithium abundances are presented for a sample of 181 nearby F and Gdwarfs with accurate Hipparcos parallaxes. The stars are on circularorbits about the Galactic centre and, hence, are identified as belongingto the thin disc. This sample is combined with two published surveys toprovide a catalogue of lithium abundances, metallicities ([Fe/H]),masses, and ages for 451 F-G dwarfs, almost all belonging to the thindisc. The lithium abundances are compared and contrasted with publishedlithium abundances for F and G stars in local open clusters. The fieldstars span a larger range in [Fe/H] than the clusters for which [Fe/H]~=0.0 +/- 0.2. The initial (i.e. interstellar) lithium abundance of thesolar neighbourhood, as derived from stars for which astration oflithium is believed to be unimportant, is traced from logɛ(Li) =2.2 at [Fe/H]=-1 to logɛ(Li) = 3.2 at +0.1. This form for theevolution is dependent on the assumption that astration of lithium isnegligible for the stars defining the relation. An argument is advancedthat this latter assumption may not be entirely correct, and, theevolution of lithium with [Fe/H] may be flatter than previouslysupposed. A sharp Hyades-like Li dip is not seen among the field starsand appears to be replaced by a large spread among lithium abundances ofstars more massive than the lower mass limit of the dip. Astration oflithium by stars of masses too low to participate in the Li dip isdiscussed. These stars show little to no spread in lithium abundance ata given [Fe/H] and mass.
| The Indo-US Library of Coudé Feed Stellar Spectra
We have obtained spectra for 1273 stars using the 0.9 m coudéfeed telescope at Kitt Peak National Observatory. This telescope feedsthe coudé spectrograph of the 2.1 m telescope. The spectra havebeen obtained with the no. 5 camera of the coudé spectrograph anda Loral 3K×1K CCD. Two gratings have been used to provide spectralcoverage from 3460 to 9464 Å, at a resolution of ~1 Å FWHMand at an original dispersion of 0.44 Å pixel-1. For885 stars we have complete spectra over the entire 3460 to 9464 Åwavelength region (neglecting small gaps of less than 50 Å), andpartial spectral coverage for the remaining stars. The 1273 stars havebeen selected to provide broad coverage of the atmospheric parametersTeff, logg, and [Fe/H], as well as spectral type. The goal ofthe project is to provide a comprehensive library of stellar spectra foruse in the automated classification of stellar and galaxy spectra and ingalaxy population synthesis. In this paper we discuss thecharacteristics of the spectral library, viz., details of theobservations, data reduction procedures, and selection of stars. We alsopresent a few illustrations of the quality and information available inthe spectra. The first version of the complete spectral library is nowpublicly available from the National Optical Astronomy Observatory(NOAO) via ftp and http.
| 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
| Non-LTE Analysis of the Sodium Abundance of Metal-Poor Stars in the Galactic Disk and Halo
We performed an extensive non-LTE analysis of the neutral sodium linesof Na I 5683/5688, 5890/5896, 6154/6161, and 8183/8195 in disk/halostars of types F-K covering a wide metallicity range (-4 <≈[Fe/H] <≈ +0.4), using our own data as well as data collectedfrom the literature. For comparatively metal-rich disk stars (-1<≈ [Fe/H] <≈ +0.4) where the weaker 6154/6161 linesare the best abundance indicators, we confirmed [Na/Fe] 0 with an"upturn" (i.e., a shallow/broad dip around -0.5 <≈ [Fe/H]<≈ 0) as already reported in previous studies. For themetal-deficient halo stars, where the much stronger 5890/5896 or8183/8195 lines subject to considerable (negative) non-LTE correctionsamounting to 0.5 dex have to be used, our analysis suggests mildly"subsolar" [Na/Fe] values down to -0.4 (with a somewhat largescatter of ± 0.2 dex) on the average at the typical halometallicity of [Fe/H] -2, followed by a rise again to a near-solarratio of [Na/Fe] 0 at the very metal-poor regime [Fe/H] -3to -4. These results are discussed in comparison with the previousobservational studies along with the theoretical predictions from theavailable chemical evolution models.
| The Nature of Overluminous F Stars Observed in a Radial-Velocity Survey
We have conducted a radial-velocity survey of bright (V<9),overluminous, F stars within 80 pc. The criterion of overluminosity isΔMc0=Mc0-MV>=0.5,where MV is the absolute magnitude based on the Hipparcosparallax and Mc0 is the absolute magnitude fromuvby photometry. For F stars, overluminosity at a level ofΔMc0>0.15 has been argued to beindicative of the presence of a bright companion, so many of theoverluminous ``single'' F stars are expected to be, in fact, binarieswith comparably bright components. Therefore, the main goals of thesurvey have been to gain insight into the nature of overluminous F starsand to test specifically the hypothesis of the duplicity of overluminousF stars by searching for previously unrecognized binary stars amongthem. Other goals of this project included the determination, whereverpossible, of the orbits of the binaries discovered as a result of thesurvey and comparing the properties of the binaries with those of thevisually single stars with constant radial velocity. The program listcomprised 111 stars that appear in the Hipparcos catalog as single, plusseven members of multiple systems whose components have individualentries in the catalog.Of the total of 118 stars selected, the radial velocities of 77 havebeen measured with the Cambridge CORAVEL in the present survey. Amongthe remainder, six have not allowed us to determine their radialvelocities because of the weakness or lack of a ``dip'' in theirradial-velocity traces, and one was optically inaccessible to thetelescope. All the rest proved to be sufficiently well known alreadyeither as binary or as constant-radial-velocity (CRV) stars. The surveydiscovered 25 new binary systems, not counting two that were notgenerally known as such but were already under observation by R. F. G.and two that were discovered by Hipparcos to show eclipses but had neverbeen recognized as SBs. With the previously known binaries, there is atotal of 61 definite plus three probable binaries out of a total of 111stars upon which we can adjudicate-a binary fraction of ~58%, justdouble the ~29% found in a sample of randomly selected F stars byNordström et al. (1997). Of the binaries, 52 are SB2 and 12 areSB1. Orbits (some of them still rather preliminary) have been determinedfor the first time for 28 binaries, 21 of which are SB2.Comparison of the CRV stars (a total of 47) with the SB2 binaries hasshown that the two groups have different kinematics. The differenceimplies that on average the CRV stars are 3 to 4 Gyr older than theSB2s, although several of the CRVs appear to be very young. At the sametime the SB2 stars turn out to have about the same kinematics, hence thesame average age, as both binary and normal single F stars from acontrol sample drawn from the Hipparcos catalog. The much older age ofthe bulk of the overluminous CRV F stars may be indicative of anomalousstellar evolution that results in anomalously long main-sequencelifetimes for those stars. The SB1 stars appear to be closer to the CRVsthan to the SB2s and are probably also very old. The properties of the``no-dip'' stars suggest very young age; some of the stars are probablypre-main-sequence (PMS). A few PMS candidates have been identified alsoamong the CRV stars. Thus, overluminous F stars comprising our sampleappear to consist of three distinct groups: mostly young SB2 binarieswith comparably bright components, mostly very old CRV and SB1 stars,and very young no-dip stars.
| 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.
| 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
| 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
| The C and N abundances in disk stars
Abundance analysis of carbon and nitrogen has been performed for asample of 90 F and G type main-sequence disk stars with a metallicityrange of -1.0 < [Fe/H] <+0.2 using the \ion{C} i and N I lines. Weconfirm a moderate carbon excess in the most metal-poor disk dwarfsfound in previous investigations. Our results suggest that carbon isenriched by superwinds of metal-rich massive stars at the beginning ofthe disk evolution, while a significant amount of carbon is contributedby low-mass stars in the late stage. The observed behavior of [N/Fe] isabout solar in the disk stars, irrespective of the metallicity. Thisresult suggests that nitrogen is produced mostly by intermediate-massstars. Based on observations carried out at National Astrono- micalObservatories (Xinglong, China).
| Lithium abundances for 185 main-sequence stars: Galactic evolution and stellar depletion of lithium
We present a survey of lithium abundances in 185 main-sequence fieldstars with 5600 <~ Teff <~ 6600 K and -1.4 <~ [Fe/H]<~ +0.2 based on new measurements of the equivalent width of thelambda 6708 Li I line in high-resolution spectra of 130 stars and areanalysis of data for 55 stars from Lambert et al. (\cite{Lambert91}).The survey takes advantage of improved photometric and spectroscopicdeterminations of effective temperature and metallicity as well as massand age derived from Hipparcos absolute magnitudes, offering anopportunity to investigate the behaviour of Li as a function of theseparameters. An interesting result from this study is the presence of alarge gap in the log varepsilon (Li) - Teff plane, whichdistinguishes ``Li-dip'' stars like those first identified in the Hyadescluster by Boesgaard & Tripicco (\cite{Boesgaard86}) from otherstars with a much higher Li abundance. The Li-dip stars concentrate on acertain mass, which decreases with metallicity from about 1.4Msun at solar metallicity to 1.1 Msun at [Fe/H] =~-1.0. Excluding the Li-dip stars and a small group of lower mass starswith Teff < 5900 K and log varepsilon (Li) < 1.5, theremaining stars, when divided into four metallicity groups, may show acorrelation between Li abundance and stellar mass. The dispersion aroundthe log varepsilon (Li)-mass relation is about 0.2 dex below [Fe/H] =~-0.4 and 0.3 dex above this metallicity, which cannot be explained byobservational errors or differences in metallicity. Furthermore, thereis no correlation between the residuals of the log varepsilon (Li)-massrelations and stellar age, which ranges from 1.5 Gyr to about 15 Gyr.This suggests that Li depletion occurs early in stellar life and thatparameters other than stellar mass and metallicity affect the degree ofdepletion, e.g. initial rotation velocity and/or the rate of angularmomentum loss. It cannot be excluded, however, that a cosmic scatter ofthe Li abundance in the Galaxy at a given metallicity contributes to thedispersion in Li abundance. These problems make it difficult todetermine the Galactic evolution of Li from the data, but a comparisonof the upper envelope of the distribution of stars in the log varepsilon(Li) - [Fe/H] plane with recent Galactic evolutionary models by Romanoet al. (\cite{Romano99}) suggests that novae are a major source for theLi production in the Galactic disk; their occurrence seems to be theexplanation for the steep increase of Li abundance at [Fe/H] =~ -0.4.Based on observations carried out at Beijing Astronomical Observatory(Xinglong, PR China) and European Southern Observatory, La Silla, Chile.Table 1 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/371/943 and athttp://www.edpsciences.org
| Chemical composition of 90 F and G disk dwarfs
High resolution, high S/N spectra have been obtained for a sample of 90F and G main-sequence disk stars covering the metallicity range -1.0< [Fe/H] < +0.1, and have been analysed in a parallel way to thework of Edvardsson et al. (\cite{Edvardsson93a}) in order to re-inspecttheir results and to reveal new information on the chemical evolution ofthe Galactic disk. Compared to Edvardsson et al. the present studyincludes several improvements. Effective temperatures are based on theAlonso et al. (\cite{Alonso96}) calibration of color indices by theinfrared flux method and surface gravities are calculated from Hipparcosparallaxes, which also allow more accurate ages to be calculated from acomparison of M_V and T_eff with isochrones. In addition, more reliablekinematical parameters are derived from Hipparcos distances and propermotions in combination with accurate radial velocities. Finally, alarger spectral coverage, 5600 - 8800 Ä, makes it possible toimprove the abundance accuracy by studying more lines and to discussseveral elements not included in the work of Edvardsson et al. Thepresent paper provides the data and discusses some general results ofthe abundance survey. A group of stars in the metallicity range of -1.0< [Fe/H] < -0.6 having a small mean Galactocentric distance in thestellar orbits, R_m < 7 kpc, are shown to be older than the otherdisk stars and probably belong to the thick disk. Excluding these stars,a slight decreasing trend of [Fe/H] with increasing R_m and age isfound, but a large scatter in [Fe/H] (up to 0.5 dex) is present at agiven age and R_m. Abundance ratios with respect to Fe show, on theother hand, no significant scatter at a given [Fe/H] . The derivedtrends of O, Mg, Si, Ca, Ti, Ni and Ba as a function of [Fe/H] agreerather well with those of Edvardsson et al., but the overabundance of Naand Al for metal-poor stars found in their work is not confirmed.Furthermore, the Galactic evolution of elements not included inEdvardsson et al., K, V and Cr, is studied. It is concluded that theterms ``alpha elements" and ``iron-peak elements" cannot be used toindicate production and evolution by specific nucleosynthesis processes;each element seems to have a unique enrichment history. Based onobservations carried out at the Beijing Astronomical Observatory,Xinglong, PR China.}\fnmsep\thanks{ Tables~3, 4 and 5 are only availablein electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.htmlor\protect\\ http://www.edpsciences.org
| Sc and Mn abundances in disk and metal-rich halo stars
Sc and Mn abundances are determined for 119 F and G main-sequence starswith -1.4 < [Fe/H] < +0.1, representing stars from the thin disk,the thick disk and the halo. The results indicate that Sc behaves likean alpha element, showing a decreasing [Sc/Fe] with increasingmetallicity in disk stars and a dual pattern in the kinematicallyselected halo stars. In contrast, Mn shows an increase from [Mn/Fe] =~-0.5 at [Fe/H] = -1.4 to zero at solar metallicity. There appears to bea discontinuity or sharp increase of [Mn/Fe] at [Fe/H] =~ -0.7corresponding to the transition between the thick and the thin disk. Itis discussed if supernovae of Type Ia are a major source of Mn in theGalactic disk or if the trend of [Mn/Fe] vs. [Fe/H] can be explained bynucleosynthesis in Type II supernovae with a strong metallicitydependence of the yield. Based on observations carried out at theEuropean Southern Observatory, La Silla, Chile, and Beijing AstronomicalObservatory, Xinglong, China
| The galactic lithium evolution revisited
The evolution of the 7Li abundance in the Galaxy has beencomputed by means of the two-infall model of Galactic chemicalevolution. We took into account several stellar 7Li sources:novae, massive AGB stars, C-stars and Type II SNe. In particular, weadopted new theoretical yields for novae. We also took into account the7Li production from GCRs. In particular, the absolute yieldsof 7Li, as suggested by a recent reevaluation of thecontribution of GCR spallation to the 7Li abundance, havebeen adopted. We compared our theoretical predictions for the evolutionof 7Li abundance in the solar neighborhood with a newcompilation of data, where we identified the population membership ofthe stars on a kinematical basis. A critical analysis of extantobservations revealed a possible extension of the Li plateau towardshigher metallicities (up to [Fe/H] ~ -0.5 or even -0.3) with a steeprise afterwards. We conclude that 1) the 7Li contributionfrom novae is required in order to reproduce the shape of the growth ofA(Li) versus [Fe/H], 2) the contribution from Type II SNe should belowered by at least a factor of two, and 3) the 7Liproduction from GCRs is probably more important than previouslyestimated, in particular at high metallicities: by taking into accountGCR nucleosynthesis we noticeably improved the predictions on the7Li abundance in the presolar nebula and at the present timeas inferred from measures in meteorites and T Tauri stars, respectively.We also predicted a lower limit for the present time 7Liabundance expected in the bulge, a prediction which might be tested byfuture observations. Tables~3 and 4 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/Abstract.html
| Library of high and mid-resolution spectra in the CA II H & K, Hα, Hβ NA i D1, D2, and He i D3 line regions of F, G, K and M field stars
In this work we present spectroscopic observations centered in thespectral lines most widely used as optical indicators of chromosphericactivity (Hα, Hβ, Ca ii H & K, and He i D3) ina sample of F, G, K and M chromospherically inactive stars. The spectrahave been obtained with the aim of providing a library of high andmid-resolution spectra to be used in the application of the spectralsubtraction technique to obtain the active-chromosphere contribution tothese lines in chromospherically active single and binary stars. Thislibrary can also be used for spectral classification purposes. A digitalversion with all the spectra is available via ftp and the World Wide Web(WWW) in both ASCII and FITS formats. Based on observations made withthe Isaac Newton telescope and the William Herschel Telescope operatedon the island of La Palma by the Royal Greenwich Observatory at theSpanish Observatorio del Roque de Los Muchachos of the Instituto deAstrofisica de Canarias, and with the 2.2 m telescope of the CentroAstronomico Hispano-Aleman of Calar Alto (Almeria, Spain) operatedjointly by the Max Planck Institut fur Astronomie (Heidelberg) and theSpanish Comision Nacional de Astronomia. The spectra of the stars listedin Table \protect\ref{tab:par} are also available in electronic form atthe CDS via anonymous 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.
| Lithium abundances for 81 F dwarfs
Lithium abundances are presented for 81 main-sequence stars witheffective temperatures of about 5800-6700 K. A novel result of thesurvey is that, in old disk dwarfs too low in mass to belong to theLi-gap, Li is generally not depleted beyond the moderate levelattributed to the convection zone of the premain- and main-sequencephase but, when depletion occurs, it is very effective. Li-poor old diskstars at luminosities too low to be identified with the Li-gap exist,but are rare.
| ICCD speckle observations of binary stars. I - A survey for duplicity among the bright stars
A survey of a sample of 672 stars from the Yale Bright Star Catalog(Hoffleit, 1982) has been carried out using speckle interferometry onthe 3.6-cm Canada-France-Hawaii Telescope in order to establish thebinary star frequency within the sample. This effort was motivated bythe need for a more observationally determined basis for predicting thefrequency of failure of the Hubble Space Telescope (HST) fine-guidancesensors to achieve guide-star lock due to duplicity. This survey of 426dwarfs and 246 evolved stars yielded measurements of 52 newly discoveredbinaries and 60 previously known binary systems. It is shown that thefrequency of close visual binaries in the separation range 0.04-0.25arcsec is 11 percent, or nearly 3.5 times that previously known.
| Spectral classification of weak-lined stars discovered photometrically
A random sample of 140 stars of the 800+ members in Olsen's (1984)sample of stars believed to be weak-lined has been observed andclassified independently of knowledge of the stars' photometriccharacteristics. It is found that 97 percent of the proposed weak-lineddwarfs are indeed such; the remainder are composites or normal, moreluminous stars. Deficiencies in the metallic-line types are comparedwith (Fe/H) values and metallic strength indices. These comparisons showthat a metal deficiency of at least a factor of two is needed before thespectra look weak-lined.
| A Search for Maia Variables
Not Available
| Prediction of spectral classification from photometric observations - Application of the UVBY beta photometry and the MK spectra classification. II - General case
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1980A&A....85...93M&db_key=AST
| Prediction of spectral classification from photometric observations-application to the UVBY beta photometry and the MK spectral classification. I - Prediction assuming a luminosity class
An algorithm based on multiple stepwise and isotonic regressions isdeveloped for the prediction of spectral classification from photometricdata. The prediction assumes a luminosity class with reference touvbybeta photometry and the MK spectral classification. The precisionattained is about 90 percent and 80 percent probability of being withinone spectral subtype respectively for luminosity groups I and V and forluminosity groups III and IV. A list of stars for which discrepanciesappear between photometry and spectral classification is given.
| Erratum : MK classification for F- and G-type stars. II.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970AJ.....75..507H&db_key=AST
| MK classifications for F-and G-type stars. II.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970AJ.....75..165H&db_key=AST
| Flux Measurements at the Centers of Stellar h- and K-Lines
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1968ApJ...153..221W&db_key=AST
| Studies of Stellar Rotation. V. The Dependence of Rotation on Age among Solar-Type Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1967ApJ...150..551K&db_key=AST
|
הכנס מאמר חדש
לינקים קשורים
הכנס לינק חדש
משמש של הקבוצה הבאה
|
תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | הרקולס |
| התרוממות ימנית: | 18h14m44.00s |
| סירוב: | +29°12'26.0" |
| גודל גלוי: | 6.56 |
| מרחק: | 41.946 פארסק |
| תנועה נכונה: | 11.8 |
| תנועה נכונה: | -240.5 |
| B-T magnitude: | 7.191 |
| V-T magnitude: | 6.571 |
קטלוגים וכינוים:
|
