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Revisiting two local constraints of the Galactic chemical evolution
I review the uncertainties in two observational local constraints of theGalactic disc chemical evolution: the metallicity distribution oflong-lived dwarfs and the age-metallicity relation. Analysing mostrecent data, it is shown first that the observed metallicitydistribution at solar galactocentric radius, designed with standardmethods, is more fit to a closed-box model than to the infallmetallicity distribution. We argue that this is due to the specificcontribution of the thick-disc population, which has been overlookedboth in the derivation of the observed metallicity distribution and inthe standard chemical evolution models. Although this agreementdisqualifies the metallicity distribution as the best supportive(indirect) evidence for infall, we argue that the evolution must be morecomplex than described by either the closed-box or the standard infallmodels.It is then shown that recent determinations of the age-metallicitydistribution (AMD) from large Strömgren photometric surveys aredominated by noise resulting from systematic biases in metallicities andeffective temperatures. These biases are evaluated and a new AMD isobtained, where particularities of the previous determinations arephased out. The new age-metallicity relation shows a mean increaselimited to about a factor of 2 in Z over the disc age. It is shown thatbelow 3 Gyr, the dispersion in metallicity is about 0.1 dex, which,given the observational uncertainties in the derived metallicities, iscompatible with the small cosmic dispersion measured on the interstellarmedium and meteoritic pre-solar dust grains. A population that isprogressively older and more metal rich arises at a metallicity greaterthan that of the Hyades, to reach [Fe/H] ~ +0.5 dex at ages greater than5 Gyr. We suggest that this is best explained by radial migration. Asymmetrical widening of the metallicity interval towards lower values isseen at about the same age, which is attributed to a similar cause.Finally, the new derived ages are sufficiently consistent that anage-metallicity relation within the thick disc is confirmed. These newfeatures altogether draw a picture of the chemical evolution in thesolar neighbourhood where dynamical effects and complexity in the AMDdominate, rather than a generalized high dispersion at all ages.
| 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.
| Synthetic Lick Indices and Detection of α-enhanced Stars. III. F, G, and K Stars with [Fe/H] > 0.00
A sample of 119 F, G, and K solar neighborhood stars, selected under thecondition [Fe/H]>0.00, is investigated in order to detect which ofthem, if any, present α-enhanced characteristics. According to thekinematics, the sample represents stars of the thin-disk component ofthe Galaxy. The search of α-enhanced characteristics is performedby adopting an already tested procedure that does not require previousknowledge of the stellar main atmospheric parameters. The analysis isbased on the comparison of spectral indices in the Lick IDS system,coming from different observational data sets, with synthetic onescomputed with solar-scaled abundances and with α-elementenhancement. The main result of the analysis is the extreme paucity(likely just one in 119) of α-enhanced stars in our sample, thussuggesting [α/Fe]=0.0 for thin-disk stars with [Fe/H]>0.00.This result, which is in agreement with the standard evolutionarypicture of the disk of the Galaxy, is compared with recent results fromhigh-resolution analysis reported in the literature. The role of theatmospheric parameter assumptions in the analysis of high-resolutionspectroscopic data is discussed, and a possible explanation ofdiscrepant results about α-enhancement for stars with[Fe/H]>0.00 is presented.
| 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.
| The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of 14 000 F and G dwarfs
We present and discuss new determinations of metallicity, rotation, age,kinematics, and Galactic orbits for a complete, magnitude-limited, andkinematically unbiased sample of 16 682 nearby F and G dwarf stars. Our63 000 new, accurate radial-velocity observations for nearly 13 500stars allow identification of most of the binary stars in the sampleand, together with published uvbyβ photometry, Hipparcosparallaxes, Tycho-2 proper motions, and a few earlier radial velocities,complete the kinematic information for 14 139 stars. These high-qualityvelocity data are supplemented by effective temperatures andmetallicities newly derived from recent and/or revised calibrations. Theremaining stars either lack Hipparcos data or have fast rotation. Amajor effort has been devoted to the determination of new isochrone agesfor all stars for which this is possible. Particular attention has beengiven to a realistic treatment of statistical biases and errorestimates, as standard techniques tend to underestimate these effectsand introduce spurious features in the age distributions. Our ages agreewell with those by Edvardsson et al. (\cite{edv93}), despite severalastrophysical and computational improvements since then. We demonstrate,however, how strong observational and theoretical biases cause thedistribution of the observed ages to be very different from that of thetrue age distribution of the sample. Among the many basic relations ofthe Galactic disk that can be reinvestigated from the data presentedhere, we revisit the metallicity distribution of the G dwarfs and theage-metallicity, age-velocity, and metallicity-velocity relations of theSolar neighbourhood. Our first results confirm the lack of metal-poor Gdwarfs relative to closed-box model predictions (the ``G dwarfproblem''), the existence of radial metallicity gradients in the disk,the small change in mean metallicity of the thin disk since itsformation and the substantial scatter in metallicity at all ages, andthe continuing kinematic heating of the thin disk with an efficiencyconsistent with that expected for a combination of spiral arms and giantmolecular clouds. Distinct features in the distribution of the Vcomponent of the space motion are extended in age and metallicity,corresponding to the effects of stochastic spiral waves rather thanclassical moving groups, and may complicate the identification ofthick-disk stars from kinematic criteria. More advanced analyses of thisrich material will require careful simulations of the selection criteriafor the sample and the distribution of observational errors.Based on observations made with the Danish 1.5-m telescope at ESO, LaSilla, Chile, and with the Swiss 1-m telescope at Observatoire deHaute-Provence, France.Complete Tables 1 and 2 are only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/418/989
| Statistical cataloging of archival data for luminosity class IV-V stars. II. The epoch 2001 [Fe/H] catalog
This paper describes the derivation of an updated statistical catalog ofmetallicities. The stars for which those metallicities apply are ofspectral types F, G, and K, and are on or near the main sequence. Theinput data for the catalog are values of [Fe/H] published before 2002February and derived from lines of weak and moderate strength. Theanalyses used to derive the data have been based on one-dimensional LTEmodel atmospheres. Initial adjustments which are applied to the datainclude corrections to a uniform temperature scale which is given in acompanion paper (see Taylor \cite{t02}). After correction, the data aresubjected to a statistical analysis. For each of 941 stars considered,the results of that analysis include a mean value of [Fe/H], an rmserror, an associated number of degrees of freedom, and one or moreidentification numbers for source papers. The catalog of these resultssupersedes an earlier version given by Taylor (\cite{t94b}).Catalog is only available in electronic form at the CDS via anonymousftp cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/398/731
| Statistical cataloging of archival data for luminosity class IV-V stars. I. The epoch 2001 temperature catalog
This paper is one of a pair in which temperatures and metallicitycatalogs for class IV-V stars are considered. The temperature catalogdescribed here is derived from a calibration based on stellar angulardiameters. If published calibrations of this kind are compared by usingcolor-index transformations, temperature-dependent differences among thecalibrations are commonly found. However, such differences are minimizedif attention is restricted to calibrations based on Johnson V-K. Acalibration of this sort from Di Benedetto (\cite{dib98}) is thereforetested and adopted. That calibration is then applied to spectroscopicand photometric data, with the latter predominating. Cousins R-Iphotometry receives special attention because of its high precision andlow metallicity sensitivity. Testing of temperatures derived from thecalibration suggests that their accuracy and precision are satisfactory,though further testing will be warranted as new results appear. Thesetemperatures appear in the catalog as values of theta equiv5040/T(effective). Most of these entries are accompanied by measured orderived values of Cousins R-I. Entries are given for 951 stars.Catalog is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/398/721
| K dwarfs and the chemical evolution of the solar cylinder
K dwarfs have lifetimes older than the present age of the Galactic disc,and are thus ideal stars for investigating the chemical evolution of thedisc. We have developed several photometric metallicity indicators for Kdwarfs, based on a sample of accurate spectroscopic metallicities for 34disc and halo G and K dwarfs. The photometric metallicities lead us todevelop a metallicity index for K dwarfs based only on their position inthe colour-absolute-magnitude diagram. Metallicities have beendetermined for 431 single K dwarfs drawn from the Hipparcos catalogue,selecting the stars by absolute magnitude and removing multiple systems.The sample is essentially a complete reckoning of the metal content innearby K dwarfs. We use stellar isochrones to mark the stars by mass,and select a subset of 220 of the stars, which is complete within anarrow mass interval. We fit the data with a model of the chemicalevolution of the solar cylinder. We find that only a modest cosmicscatter is required to fit our age-metallicity relation. The modelassumes two main infall episodes for the formation of the halo-thickdisc and thin disc, respectively. The new data confirm that the solarneighbourhood formed on a long time-scale of the order of 7 Gyr.
| Abundances in metal-rich stars. Detailed abundance analysis of 47 G and K dwarf stars with [Me/H] > 0.10 dex
We have derived elemental abundances of O, Na, Mg, Al, Si, Ca, Ti, Cr,Mn, Fe, Co, Ni as well as for a number of s-elements for 47 G and Kdwarf, with [Me/H]>0.1 dex. The selection of stars was based on theirkinematics as well as on their uvby-beta photometry. One sample of starson rather eccentric orbits traces the chemical evolution interior to thesolar orbit and another, on circular orbits, the evolution around thesolar orbit. A few Extreme Population I stars were included in thelatter sample. The stars have -0.1 dex < [Fe/H] < 0.42 dex. Thespectroscopic [Fe/H] correlate well with the [Me/H] derived fromuvby-beta photometry. We find that the elemental abundances of Mg, Al,Si, Ca, Ti, Cr and Ni all follow [Fe/H]. Our data put furtherconstraints on models of galactic chemical evolution, in particular ofCr, Mn and Co which have not previously been studied for dwarf starswith [Me/H] >0.1 dex. The increase in [Na/Fe] and [Al/Fe] as afunction of [Fe/H] found previously by \cite[Edvardsson et al.(1993a)]{Edv93} has been confirmed for [Na/Fe]. This upturning relation,and the scatter around it, are shown not to be due to a mixture ofpopulations with different mean distances to the galactic centre. We donot confirm the same trend for aluminium, which is somewhat surprisingsince both these elements are thought to be produced in the sameenvironments in the pre-supernova stars. Nor have we been able to traceany tendency for relative abundances of O, Si, and Ti relative to Fe tovary with the stellar velocities, i.e. the stars present mean distanceto the galactic centre. These results imply that there is no significantdifference in the chemical evolution of the different stellarpopulations for stars with [Me/H]>0.1 dex. We find that [O/Fe]continue to decline with increasing [Fe/H] and that oxygen and europiumcorrelate well. However [Si/Fe] and [Ca/Fe] seem to stay constant. Areal (``cosmic'') scatter in [Ti/Fe] at given [Fe/H] is suggested aswell as a decreasing abundance of the s-elements relative to iron forthe most metal-rich dwarf stars. We discuss our results in the contextof recent models of galactic chemical evolution. In our sample we haveincluded a few very metal rich stars, sometimes called SMR (super metalrich) stars. We find these stars to be among the most iron-rich in oursample but far from as metal-rich as indicated by their photometricmetallicities. SMR stars on highly eccentric orbits, alleged to tracethe evolution of the chemical evolution in the galactic Bulge, havepreviously been found overabundant in O, Mg and Si. We have includedthree such stars from the study by \cite[Barbuy & Grenon(1990)]{Bar90}. We find them to be less metal rich and the otherelemental abundances remain puzzling. Detailed spectroscopic abundanceanalyses of K dwarf stars are rare. Our study includes 5 K dwarf starsand has revealed what appears to be a striking example ofoverionization. The overionization is especially prominent for Ca, Crand Fe. The origin of this apparent overionization is not clear and wediscuss different explanations in some detail. Based on observations atthe McDonald Observatory.
| Stars with large Proper Motions in the Hyderabab Astrographic zones + 36° to + 39° (Final list)
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Pozíciós és asztrometriai adatok
| Csillagkép: | Ökörhajcsár |
| Rektaszcenzió: | 15h08m58.74s |
| Deklináció: | +37°19'06.8" |
| Vizuális fényesség: | 8.844 |
| Távolság: | 40.683 parszek |
| RA sajátmozgás: | 66.6 |
| Dec sajátmozgás: | 102 |
| B-T magnitude: | 9.902 |
| V-T magnitude: | 8.932 |
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