Contents
Images
Upload your image
DSS Images Other Images
Related articles
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.
| Beryllium Abundances in F and G Dwarfs in Praesepe and Other Young Clusters from Keck HIRES Observations
The study of both Be and Li gives useful clues about stellar internalstructure. Of particular interest is the study of these light elementsin open clusters, which have a known age and metallicity. In this paperwe present a study of Be abundances in 10 F-type stars in Praesepe and acomprehensive discussion about Be abundances in other open clusters:Hyades, Pleiades, α Per, Coma, and UMa. We have made observationsof the doublet of Be II around 3130 Å in Praesepe stars, using theKeck I telescope and the High Resolution Echelle Spectrometer (HIRES).Beryllium abundances were derived from the spectra using the spectrumsynthesis method. We find four stars with definite Be depletion in thetemperature range of the Li dip like we found in our previous clusterstudies, notably for the Hyades and Coma clusters. Putting all theclusters together, we confirm the existence of a Be dip in a narrowtemperature range for F stars. Beryllium depletion in this dip is lesspronounced than Li depletion. For the cooler stars there is little or noBe depletion, even though there are large depletions of Li. For starsthat have little or no Li depletion, A(Li)>=3.0, the ratio Li/Be is75+/-4.6, compared to the meteoritic ratio of 77.6. For stars coolerthan ~5900 K there appears to be little or no Be depletion, and the meanA(Be) is 1.30+/-0.02. For these cooler stars within a given clusterthere is no evidence for intrinsic star-to-star differences in A(Be),with the possible exception of the cool Pleiades stars. In thetemperature range of the Li-Be dip, a strong correlation exists betweenLi and Be, consistent with the theory of rotationally induced mixing.Moreover, the slopes of the Li versus Be correlations are differentdepending on the temperature range. For the full sample of 42 starsbetween 5900 and 6650 K the slope is 0.43+/-0.05 [where A(Li) is theabscissa]. The slope is 0.48+/-0.08 for 6300K
| 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
| Beryllium in the Hyades F and G Dwarfs from Keck HIRES Spectra
Although there are extensive observations of Li in field stars of alltypes and in both open and (recently) globular cluster stars, there arerelatively few observations of Be. Because Be is not destroyed as easilyas Li, the abundances of Li and Be together can tell us more about theinternal physical processes in stars than either element can alone. Wehave obtained high-resolution (45,000) and high signal-to-noise ratio(typically 90 per pixel) spectra of the Be II resonance lines in 34Hyades F and G dwarfs with the Keck I telescope and HIRES. In additionwe took a spectrum of the daytime sky to use as a surrogate for thesolar spectrum so we could determine the value for Be in the Sun,analyzed in the same manner as that for the stars. We have adoptedstellar temperatures and some Li abundances for these stars from theliterature. For most of the F dwarfs we have rederived Li abundances.The Be abundances have been derived with the spectrum synthesis method.We find that Be is depleted, but detected, in the Li gap in the F starsreaching down to values of A(Be)=0.60 dex, or a factor of nearly 7 belowthe meteoritic Be abundance (a factor of 3.5 below the solar value ofChmielewski et al.). There is little or no depletion of Be in starscooler than 6000 K, in spite of the large depletions (0.5-2.5 dex) inLi. The mean value of A(Be) for the 10 coolest stars is 1.33+/-0.06, notfar from the meteoritic value of 1.42. The pattern in the Beabundances-a Be dip and undepleted Be in the cool stars-is well matchedby the predictions of slow mixing due to stellar rotation. We haveinterpolated the calculations of Deliyannis and Pinsonneault for Bedepletion due to rotational mixing to the age of the Hyades; we findexcellent agreement of the predictions with the observed Be abundancesbut less good agreement with the observed Li abundances. Some of ourHyades stars have photometrically determined rotation periods, but thereis no relation between Be and rotation period. (Generally, the lowermass stars have less Li and longer periods, which may indicate greaterspin-down and thus more Li depletion relative to Be.) The Li and Beabundances are correlated for stars in the temperature range of5850-6680 K, similar to results from earlier work on Li and Be in F andG field stars. This indicates that the depletions are not justcorrelated-the only claim that can be made for the field stars-but areprobably occurring together during main-sequence evolution. The Hyades Gdwarfs have more Be than the Sun; their initial Be may have been largeror they may not be old enough to have depleted much Be. For those Hyadesstars that seem to have little or no depletion of Li or Be, the Li/Beratio is found to be 75+/-30 the meteoritic ratio Li/Be is 78. TheHyades ratio is a representative value for the initial ratio in thematerial out of which the Hyades cluster was formed.
| 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
| A Hipparcos study of the Hyades open cluster. Improved colour-absolute magnitude and Hertzsprung-Russell diagrams
Hipparcos parallaxes fix distances to individual stars in the Hyadescluster with an accuracy of ~ 6 percent. We use the Hipparcos propermotions, which have a larger relative precision than the trigonometricparallaxes, to derive ~ 3 times more precise distance estimates, byassuming that all members share the same space motion. An investigationof the available kinematic data confirms that the Hyades velocity fielddoes not contain significant structure in the form of rotation and/orshear, but is fully consistent with a common space motion plus a(one-dimensional) internal velocity dispersion of ~ 0.30 kms-1. The improved parallaxes as a set are statisticallyconsistent with the Hipparcos parallaxes. The maximum expectedsystematic error in the proper motion-based parallaxes for stars in theouter regions of the cluster (i.e., beyond ~ 2 tidal radii ~ 20 pc) isla 0.30 mas. The new parallaxes confirm that the Hipparcos measurementsare correlated on small angular scales, consistent with the limitsspecified in the Hipparcos Catalogue, though with significantly smaller``amplitudes'' than claimed by Narayanan & Gould. We use the Tycho-2long time-baseline astrometric catalogue to derive a set of independentproper motion-based parallaxes for the Hipparcos members. The newparallaxes provide a uniquely sharp view of the three-dimensionalstructure of the Hyades. The colour-absolute magnitude diagram of thecluster based on the new parallaxes shows a well-defined main sequencewith two ``gaps''/``turn-offs''. These features provide the first directobservational support of Böhm-Vitense's prediction that (the onsetof) surface convection in stars significantly affects their (B-V)colours. We present and discuss the theoretical Hertzsprung-Russelldiagram (log L versus log T_eff) for an objectively defined set of 88high-fidelity members of the cluster as well as the delta Scuti startheta 2 Tau, the giants delta 1, theta1, epsilon , and gamma Tau, and the white dwarfs V471 Tau andHD 27483 (all of which are also members). The precision with which thenew parallaxes place individual Hyades in the Hertzsprung-Russelldiagram is limited by (systematic) uncertainties related to thetransformations from observed colours and absolute magnitudes toeffective temperatures and luminosities. The new parallaxes providestringent constraints on the calibration of such transformations whencombined with detailed theoretical stellar evolutionary modelling,tailored to the chemical composition and age of the Hyades, over thelarge stellar mass range of the cluster probed by Hipparcos.
| Color indices of the Sun and Hyades stars in the WBVR system
Using an original setup at high altitudes, we measured the color indicesof the Sun in the WBVR photometric system relative to standard stars: (W- B)_solar = -0.05, (B - V)_solar = +0.67, and (V - R)_solar = +0.53. Wepresent the WBVR photometry for the Hyades members selected by vanBueren by their space velocities. The solar position is shown intwo-color diagrams relative to Hyades stars and bright G2 V stars. Acomparison of our results with Kurucz's models reveals a discrepancybetween the metallicities of the models and the Hyades members.
| The Hyades: distance, structure, dynamics, and age
{We use absolute trigonometric parallaxes from the Hipparcos Catalogueto determine individual distances to members of the Hyades cluster, fromwhich the 3-dimensional structure of the cluster can be derived.Inertially-referenced proper motions are used to rediscuss distancedeterminations based on convergent-point analyses. A combination ofparallaxes and proper motions from Hipparcos, and radial velocities fromground-based observations, are used to determine the position andvelocity components of candidate members with respect to the clustercentre, providing new information on cluster membership: 13 newcandidate members within 20 pc of the cluster centre have beenidentified. Farther from the cluster centre there is a gradual mergingbetween certain cluster members and field stars, both spatially andkinematically. Within the cluster, the kinematical structure is fullyconsistent with parallel space motion of the component stars with aninternal velocity dispersion of about 0.3 km s(-1) . The spatialstructure and mass segregation are consistent with N-body simulationresults, without the need to invoke expansion, contraction, rotation, orother significant perturbations of the cluster. The quality of theindividual distance determinations permits the cluster zero-age mainsequence to be accurately modelled. The helium abundance for the clusteris determined to be Y =3D 0.26+/-0.02 which, combined with isochronemodelling including convective overshooting, yields a cluster age of625+/-50 Myr. The distance to the observed centre of mass (a conceptmeaningful only in the restricted context of the cluster memberscontained in the Hipparcos Catalogue) is 46.34+/-0.27 pc, correspondingto a distance modulus m-M=3D3.33+/-0.01 mag for the objects within 10 pcof the cluster centre (roughly corresponding to the tidal radius). Thisdistance modulus is close to, but significantly better determined than,that derived from recent high-precision radial velocity studies,somewhat larger than that indicated by recent ground-based trigonometricparallax determinations, and smaller than those found from recentstudies of the cluster convergent point. These discrepancies areinvestigated and explained. } Based on observations made with the ESAHipparcos astrometry satellite. Table~2 is also 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
| 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
| The role of convection on the UVBY colours of A, F, and G stars
We discuss the effects of convection on the theoretical uvby colours ofA, F, and G stars. The standard mixing-length theory atlas9 models ofKurucz (1993), with and without approximate overshooting, are comparedto models using the turbulent convection theory proposed by Canuto &Mazzitelli (1991, 1992) and implemented by Kupka (1996a). Comparisonwith fundamental T_eff and log g stars reveals that the Canuto &Mazzitelli models give results that are generally superior to standardmixing-length theory (MLT) without convective overshooting. MLT modelswith overshooting are found to be clearly discrepant. This is supportedby comparisons of non-fundamental stars, with T_eff obtained from theInfrared Flux Method and log g from stellar evolutionary models for opencluster stars. The Canuto & Mazzitelli theory gives values of(b-y)_0 and c_0 that are in best overall agreement with observations.Investigations of the m_0 index reveal that all of the treatments ofconvection presented here give values that are significantly discrepantfor models with T_eff < 6000 K. It is unclear as to whether this isdue to problems with the treatment of convection, missing opacity, orsome other reason. None of the models give totally satisfactory m_0indices for hotter stars, but the Canuto & Mazzitelli models are inclosest overall agreement above 7000 K. Grids of uvby colours, based onthe CM treatment of convection, are presented. These grids represent animprovement over the colours obtained from models using themixing-length theory. The agreement with fundamental stars enables thecolours to be used directly without the need for semi-empiricaladjustments that were necessary with the earlier colour grids. Table~5is only available at the CDS via anonymous ftp 130.79.128.5 or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Stellar Oxygen Abundances.V.Abundances of Two Hyades Dwarfs Derived from the 6300 Angstroms [OI] Line
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....112.2650K&db_key=AST
| The Lithium Dip in M67: Comparison with the Hyades, Praesepe, and NGC 752 Clusters
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...446..203B&db_key=AST
| 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.
| Radio continuum emission from stars: a catalogue update.
An updated version of my catalogue of radio stars is presented. Somestatistics and availability are discussed.
| Analyses of archival data for cool dwarfs. 2: A catalog of temperatures
A calibration presented in a previous paper is used in this paper toderive temperatures for FGK stars near the main sequence. Thecalibration is checked against published counterparts, and it is foundthat previous calibrations have not established K-dwarf temperatures inparticular beyond reasonable doubt. The database assembled to derive thetemperatures is described, and the problems posed by close binaries areevaluated. The newly derived temperatures are used to check a line-depthratio proposed as a thermometer by Gray and Johanson (1991, PASP, 103,439), and it is found that the ratio is metallicity-sensitive.Temperatures are given for a total of 417 stars.
| Stroemgren photometry of F- and G-type stars brighter than V = 9.6. I. UVBY photometry
Within the framework of a large photometric observing program, designedto investigate the Galaxy's structure and evolution, Hβ photometryis being made for about 9000 stars. As a by-product, supplementary uvbyphotometry has been made. The results are presented in a cataloguecontaining 6924 uvby observations of 6190 stars, all south ofδ=+38deg. The overall internal rms errors of one observation(transformed to the standard system) of a program star in the interval6.5
| Oxygen abundances in F-type stars of the Hyades and the Ursa Major group
We have derived the oxygen abundances of 50 F-type main-sequence stars,belonging to the Hyades open cluster, the Ursa Major group, and thefield, using an NLTE analysis of the infrared triplet lines of O I at7771-7775 AA. The stars of the middle F-range have previously been shownto exhibit a marked reduction in lithium abundance compared with bothcooler and hotter objects in the same systems: the 'Li gap', for whichseveral explanations have been proposed. Our results here show asubstantial measure of uniformity in the oxygen abundances over therange in T(eff) between 5800 and 7400 K. The data might indicate a smalldip (less than 0.1 dex) in the oxygen abundance for stars located in theLi gap. Microscopic diffusion seems to be the only known mechanism ableto produce an oxygen dip. If this mechanism were also responsible forthe Li gap, it would have to account for a depletion of up to two ordersof magnitude in lithium and, at the same time, less than 0.1 dex inoxygen. We note, however, that turbulent mixing could modify amicroscopic diffusion pattern in order to yield the observed abundances.
| A Study of Activity in F-Type Main-Sequence Stars Using the D/3 Line of Hei
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&A...273..482G&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.
| CA II H and K measurements made at Mount Wilson Observatory, 1966-1983
Summaries are presented of the photoelectric measurements of stellar CaII H and K line intensity made at Mount Wilson Observatory during theyears 1966-1983. These results are derived from 65,263 individualobservations of 1296 stars. For each star, for each observing season,the maximum, minimum, mean, and variation of the instrumental H and Kindex 'S' are given, as well as a measurement of the accuracy ofobservation. A total of 3110 seasonal summaries are reported. Factorswhich affect the ability to detect stellar activity variations andaccurately measure their amplitudes, such as the accuracy of the H and Kmeasurements and scattered light contamination, are discussed. Relationsare given which facilitate intercomparison of 'S' values with residualintensities derived from ordinary spectrophotometry, and for convertingmeasurements to absolute fluxes.
| Lithium, age, and metallicity in open clusters
It is shown that a strong relationship exists between Li abundance andage for stars in the temperature region 5950-6350 K. The relation isderived from mean Li abundances in eight open clusters ranging in agefrom 5 x 10 to the 7th to 8 x 10 to the 9th yr. The Li declinesexponentially with t exp(-0.3). It is suggested that, in thistemperature regime, simple microscopic diffusion is the cause of the Lidepletion. It is possible that there is a metallicity term in therelation, such that higher metallicity clusters with deeper convectionzones have less Li depletion, while lower metallicity cluster undergogreater depletion. This is consistent with expectations from diffusiontheory. Furthermore, the halo stars, with even lower metallicity andshallower convection zones, would have more diffusion and more Lidepletion; this is in agreement with recent theoretical work.
| Early type high-velocity stars in the solar neighborhood. IV - Four-color and H-beta photometry
Results are presented from photometric obaservations in the Stromgrenuvby four-color and H-beta systems of early-type high-velocity stars inthe solar neighborhood. Several types of photometrically peculiar starsare selected on the basis of their Stromgren indices and areprovisionally identified as peculiar A stars, field horizontal-branchstars, metal-poor stars near the Population II and old-disk turnoffs,metal-poor blue stragglers, or metallic-line A stars. Numerousphotometrically normal stars were also found.
| The distance and main sequence of the Hyades cluster based on 145 stars with highly accurate proper motions obtained from work on the catalogues FK 5 and PPM
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1991A&A...243..386S&db_key=AST
| Chemical abundances and ages of open clusters
The metal content of nine open clusters is discussed with the help ofresults from detailed spectral analyses of main-sequence and slightlyevolved stars, belonging to those clusters. This small sample ofclusters, out of about 1200 known, has, however, the advantage ofrepresenting the whole span of ages of open clusters with two young(Alpha Per, the Pleiades, with five intermediate age, including U Ma,Hyades, Coma, Praesepe, and NGC 752) and with two old (M 67 and NGC 188)clusters. It has also the advantage that the observations of almost allthe stars in these different clusters have been carried out on similar,when not identical telescopes, on similar high-resolution spectrographs,and similar detectors. The high signal/noise spectra of these clusterstars have been reduced with similar procedures, and interpreted withsimilar model atmosphere analyses. In taking into account the error barsattributed to the mean metal content parameter, Fe/H, of each cluster,one may conclude that only the Hyades cluster has a metal content whichdiffers significantly from that of the sun, being between 30 and 40percent higher than that of the sun.
| Chemical composition of open clusters. I - Fe/H from high-resolution spectroscopy
Using high-resolution spectroscopy, the abundance ratios Fe/H, C/H, andC/Fe were determined for F dwarfs in the Alpha Per, the Pleiades, andthe Hyades clusters; the UMa, Hyades, and Wolf 630 moving groups; and aselection of bright F field dwarfs. The age span of these objects rangesfrom 5 x 10 to the 7th to 2 x 10 to the 9th yr. No evidence was found ofa trend in Fe/H with age for these clusters and groups, but there wereclear differences in Fe/H among these groups, indicating intrinsicdifferences in the metal content of the local gas out of which thesegroups were formed. No evidence was found for a trend of C/H with age ofthese stellar groups, but there were cluster-to-cluster variations,implying differences in the content of carbon in the precluster gas. TheC/H cluster differences followed the same pattern as the Fe/H clusterdifferences and yield C/Fe values which are constant, and equal to thesolar value, in all the groups.
| New calibrations of blanketing parameters Delta m2 and delta m1 in terms of Fe/H
New calibrations are derived for the blanketing parameters Delta m2 anddelta m1, of the Geneva and Stromgren photometric system, respectively,in terms of Fe/H. Based on a sample of 164 A-F main-sequence and giantstars, two quadratics relations in a metallicity range from -2.13 to 0.5are defined.
| Determining the temperatures of solar-type stars - Do star spots produce color anomalies?
The available evidence pertaining to color 'anomalies' in Hyades dwarfsare examined in detail in order to understand how the determine thetemperatures of solar-type stars. The evidence indicates that thetemperatures of these stars are not seriously skewed by their spots.Simpler explanations which can produce the observed effects arediscussed.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | Stier |
| Right ascension: | 04h25m57.34s |
| Declination: | +05°09'00.5" |
| Apparent magnitude: | 7.363 |
| Distance: | 45.393 parsecs |
| Proper motion RA: | 94.7 |
| Proper motion Dec: | 3.8 |
| B-T magnitude: | 7.97 |
| V-T magnitude: | 7.414 |
Catalogs and designations:
|
INHABITED SKY
