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Spectroscopic Properties of Cool Stars (SPOCS). I. 1040 F, G, and K Dwarfs from Keck, Lick, and AAT Planet Search Programs
We present a uniform catalog of stellar properties for 1040 nearby F, G,and K stars that have been observed by the Keck, Lick, and AAT planetsearch programs. Fitting observed echelle spectra with synthetic spectrayielded effective temperature, surface gravity, metallicity, projectedrotational velocity, and abundances of the elements Na, Si, Ti, Fe, andNi, for every star in the catalog. Combining V-band photometry andHipparcos parallaxes with a bolometric correction based on thespectroscopic results yielded stellar luminosity, radius, and mass.Interpolating Yonsei-Yale isochrones to the luminosity, effectivetemperature, metallicity, and α-element enhancement of each staryielded a theoretical mass, radius, gravity, and age range for moststars in the catalog. Automated tools provide uniform results and makeanalysis of such a large sample practical. Our analysis method differsfrom traditional abundance analyses in that we fit the observed spectrumdirectly, rather than trying to match equivalent widths, and wedetermine effective temperature and surface gravity from the spectrumitself, rather than adopting values based on measured photometry orparallax. As part of our analysis, we determined a new relationshipbetween macroturbulence and effective temperature on the main sequence.Detailed error analysis revealed small systematic offsets with respectto the Sun and spurious abundance trends as a function of effectivetemperature that would be inobvious in smaller samples. We attempted toremove these errors by applying empirical corrections, achieving aprecision per spectrum of 44 K in effective temperature, 0.03 dex inmetallicity, 0.06 dex in the logarithm of gravity, and 0.5 kms-1 in projected rotational velocity. Comparisons withprevious studies show only small discrepancies. Our spectroscopicallydetermined masses have a median fractional precision of 15%, but theyare systematically 10% higher than masses obtained by interpolatingisochrones. Our spectroscopic radii have a median fractional precisionof 3%. Our ages from isochrones have a precision that variesdramatically with location in the Hertzsprung-Russell diagram. We planto extend the catalog by applying our automated analysis technique toother large stellar samples.
| The Planet-Metallicity Correlation
We have recently carried out spectral synthesis modeling to determineTeff, logg, vsini, and [Fe/H] for 1040 FGK-type stars on theKeck, Lick, and Anglo-Australian Telescope planet search programs. Thisis the first time that a single, uniform spectroscopic analysis has beenmade for every star on a large Doppler planet search survey. We identifya subset of 850 stars that have Doppler observations sufficient todetect uniformly all planets with radial velocity semiamplitudes K>30m s-1 and orbital periods shorter than 4 yr. From this subsetof stars, we determine that fewer than 3% of stars with-0.5<[Fe/H]<0.0 have Doppler-detected planets. Above solarmetallicity, there is a smooth and rapid rise in the fraction of starswith planets. At [Fe/H]>+0.3 dex, 25% of observed stars have detectedgas giant planets. A power-law fit to these data relates the formationprobability for gas giant planets to the square of the number of metalatoms. High stellar metallicity also appears to be correlated with thepresence of multiple-planet systems and with the total detected planetmass. This data set was examined to better understand the origin of highmetallicity in stars with planets. None of the expected fossilsignatures of accretion are observed in stars with planets relative tothe general sample: (1) metallicity does not appear to increase as themass of the convective envelopes decreases, (2) subgiants with planetsdo not show dilution of metallicity, (3) no abundance variations for Na,Si, Ti, or Ni are found as a function of condensation temperature, and(4) no correlations between metallicity and orbital period oreccentricity could be identified. We conclude that stars with extrasolarplanets do not have an accretion signature that distinguishes them fromother stars; more likely, they are simply born in higher metallicitymolecular clouds.Based on observations obtained at Lick and Keck Observatories, operatedby the University of California, and the Anglo-Australian Observatories.
| 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.
| 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.
| Resolved Inner Disks around Herbig Ae/Be Stars
We have observed 14 Herbig Ae/Be (HAEBE) sources with the long-baselinenear-IR Palomar Testbed Interferometer. All except two sources areresolved at 2.2 μm, with angular sizes generally <~5 mas. Wedetermine the size scales and orientations of the 2.2 μm emissionusing various models: uniform disks, Gaussians, uniform rings, flataccretion disks with inner holes, and flared disks with puffed-up innerrims. Although it is difficult to distinguish different radialdistributions, we are able to place firm constraints on the inclinationsof most sources; seven objects display significantly inclinedmorphologies. The inner disk inclinations derived from our near-IR dataare generally compatible with the outer disk geometries inferred frommillimeter interferometric observations, implying that HAEBE disks arenot significantly warped. Using the derived inner disk sizes andinclinations, we compute the spectral energy distributions (SEDs) fortwo simple physical disk models and compare these with observed SEDscompiled from the literature and new near-IR photometry. Whilegeometrically flat accretion disk models are consistent with the datafor the earliest spectral types in our sample (MWC 297, V1685 Cyg, andMWC 1080), the later type sources are explained better through modelsincorporating puffed-up inner disk walls. The different inner diskgeometries may indicate different accretion mechanisms for early- andlate-type HAEBE stars.
| Synthetic Lick Indices and Detection of α-enhanced Stars. II. F, G, and K Stars in the -1.0 < [Fe/H] < +0.50 Range
We present an analysis of 402 F, G, and K solar neighborhood stars, withaccurate estimates of [Fe/H] in the range -1.0 to +0.5 dex, aimed at thedetection of α-enhanced stars and at the investigation of theirkinematical properties. The analysis is based on the comparison of 571sets of spectral indices in the Lick/IDS system, coming from fourdifferent observational data sets, with synthetic indices computed withsolar-scaled abundances and with α-element enhancement. We useselected combinations of indices to single out α-enhanced starswithout requiring previous knowledge of their main atmosphericparameters. By applying this approach to the total data set, we obtain alist of 60 bona fide α-enhanced stars and of 146 stars withsolar-scaled abundances. The properties of the detected α-enhancedand solar-scaled abundance stars with respect to their [Fe/H] values andkinematics are presented. A clear kinematic distinction betweensolar-scaled and α-enhanced stars was found, although a one-to-onecorrespondence to ``thin disk'' and ``thick disk'' components cannot besupported with the present data.
| 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.
| Chemical enrichment and star formation in the Milky Way disk. III. Chemodynamical constraints
In this paper, we investigate some chemokinematical properties of theMilky Way disk, by using a sample composed by 424 late-type dwarfs. Weshow that the velocity dispersion of a stellar group correlates with theage of this group, according to a law proportional to t0.26,where t is the age of the stellar group. The temporal evolution of thevertex deviation is considered in detail. It is shown that the vertexdeviation does not seem to depend strongly on the age of the stellargroup. Previous studies in the literature seem to not have found it dueto the use of statistical ages for stellar groups, rather thanindividual ages. The possibility to use the orbital parameters of a starto derive information about its birthplace is investigated, and we showthat the mean galactocentric radius is likely to be the most reliablestellar birthplace indicator. However, this information cannot bepresently used to derive radial evolutionary constraints, due to anintrinsic bias present in all samples constructed from nearby stars. Anextensive discussion of the secular and stochastic heating mechanismscommonly invoked to explain the age-velocity dispersion relation ispresented. We suggest that the age-velocity dispersion relation couldreflect the gradual decrease in the turbulent velocity dispersion fromwhich disk stars form, a suggestion originally made by Tinsley &Larson (\cite{tinsley}, ApJ, 221, 554) and supported by several morerecent disk evolution calculations. A test to distinguish between thetwo types of models using high-redshift galaxies is proposed.Full Table 1 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/423/517
| 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
| Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 Parsecs: The Northern Sample. I.
We have embarked on a project, under the aegis of the Nearby Stars(NStars)/Space Interferometry Mission Preparatory Science Program, toobtain spectra, spectral types, and, where feasible, basic physicalparameters for the 3600 dwarf and giant stars earlier than M0 within 40pc of the Sun. In this paper, we report on the results of this projectfor the first 664 stars in the northern hemisphere. These resultsinclude precise, homogeneous spectral types, basic physical parameters(including the effective temperature, surface gravity, and overallmetallicity [M/H]), and measures of the chromospheric activity of ourprogram stars. Observed and derived data presented in this paper arealso available on the project's Web site.
| Oxygen line formation in late-F through early-K disk/halo stars. Infrared O I triplet and [O I] lines
In order to investigate the formation of O I 7771-5 and [O I] 6300/6363lines, extensive non-LTE calculations for neutral atomic oxygen werecarried out for wide ranges of model atmosphere parameters, which areapplicable to early-K through late-F halo/disk stars of variousevolutionary stages.The formation of the triplet O I lines was found to be well described bythe classical two-level-atom scattering model, and the non-LTEcorrection is practically determined by the parameters of theline-transition itself without any significant relevance to the detailsof the oxygen atomic model. This simplifies the problem in the sensethat the non-LTE abundance correction is essentially determined only bythe line-strength (Wlambda ), if the atmospheric parametersof Teff, log g, and xi are given, without any explicitdependence of the metallicity; thus allowing a useful analytical formulawith tabulated numerical coefficients. On the other hand, ourcalculations lead to the robust conclusion that LTE is totally valid forthe forbidden [O I] lines.An extensive reanalysis of published equivalent-width data of O I 7771-5and [O I] 6300/6363 taken from various literature resulted in theconclusion that, while a reasonable consistency of O I and [O I]abundances was observed for disk stars (-1 <~ [Fe/H] <~ 0), theexistence of a systematic abundance discrepancy was confirmed between OI and [O I] lines in conspicuously metal-poor halo stars (-3 <~[Fe/H] <~ -1) without being removed by our non-LTE corrections, i.e.,the former being larger by ~ 0.3 dex at -3 <~ [Fe/H] <~ -2.An inspection of the parameter-dependence of this discordance indicatesthat the extent of the discrepancy tends to be comparatively lessenedfor higher Teff/log g stars, suggesting the preference ofdwarf (or subgiant) stars for studying the oxygen abundances ofmetal-poor stars.Tables 2, 5, and 7 are only available in electronic form, at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/402/343 and Table\ref{tab3} is only available in electronic form athttp://www.edpsciences.org
| 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
| Imaging and Spatially Resolved Spectroscopy of AFGL 2688 in the Thermal Infrared Region
We present ground-based high-resolution (~0.3") imaging of AFGL 2688 atL' (3.8 μm) and M' (4.7 μm). A wealth of structure in the centralregion is revealed as a consequence of less extinction in the thermalinfrared. A clear border in the southern lobe at L' corresponds to theedge of the heavily obscured region in visible, indicating that there isa dense material surrounding the central region. The images also show anarrow dark lane oriented to 140° east of north with the normal at50°. The normal position angle is inconsistent with the opticalpolar axis (P.A.=15deg) but is aligned to the high-velocityCO components found in the radio wavelength observations. The centralstar remains invisible at L' and M'. Several clumpy regions in the northlobe dominate in L' and M' luminosity. In particular, a pointlike source(peak A) at 0.5" northeast of the center of the nebula exhibits thehighest surface brightness with a very red spectral energy distribution(SED). Based on the almost identical SED at adjacent regions, we suggestthat the pointlike source is not self-luminous, as was proposed, but isa dense dusty blob reflecting thermal emission from the central star. Wealso present spatially resolved slit spectroscopy of the bright dustyblobs. An emission feature at 3.4 μm as well as at 3.3 μm isdetected everywhere within our field of view. There is no spatialvariation in the infrared emission feature throughout the observed area(0.2"-1.5", or 240-1800 AU from the central source). The constant fluxratio of the emission feature relative to the continuum is consistentwith the view that the blobs are mostly reflecting the light from thecentral star in the 3 μm region. Based on data collected at SubaruTelescope, which is operated by the National Astronomical Observatory ofJapan.
| 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
| Europium abundances in F and G disk dwarfs
Europium abundances for 74 F and G dwarf stars of the galactic disk havebeen determined from the 4129.7 Å Eu II line. The stars wereselected from the sample of Edvardsson et al. (1993) and [Eu/Fe] shows asmaller scatter and a slightly weaker trend with [Fe/H] than found byWoolf et al. (1995). The data of the two analyses are homogenized andmerged. We also discuss the adopted effective temperature scale. Basedon observations carried out at the European Southern Observatory, LaSilla, Chile. Tables 2 and 6 are only available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcal?J/A+A/381/500
| Levels of coronal and chromospheric activity in late-type stars and various types of dynamo waves
We analyze the X-ray emission and chromospheric activity of late-type F,G, and K stars studied in the framework of the HK project. More powerfulcoronas are possessed by stars displaying irregular variations of theirchromospheric emission, while stars with cyclic activity arecharacterized by comparatively modest X-ray luminosities and ratios ofthe X-ray to bolometric luminosity L X/L bol. This indicates that thenature of processes associated with magnetic-field amplification in theconvective envelope changes appreciably in the transition from small tolarge dynamo numbers, directly affecting the character of the(α-Ω) dynamo. Due to the strong dependence of both thedynamo number and the Rossby number on the speed of axial rotation,earlier correlations found between various activity parameters and theRossby number are consistent with our conclusions. Our analysis makes itpossible to draw the first firm conclusions about the place of solaractivity among analogous processes developing in active late-type stars.
| Sixth Catalogue of Fundamental Stars (FK6). Part III. Additional fundamental stars with direct solutions
The FK6 is a suitable combination of the results of the HIPPARCOSastrometry satellite with ground-based data, measured over a longinterval of time and summarized mainly in the FK5. Part III of the FK6(abbreviated FK6(III)) contains additional fundamental stars with directsolutions. Such direct solutions are appropriate for single stars or forobjects which can be treated like single stars. Part III of the FK6contains in total 3272 stars. Their ground-based data stem from thebright extension of the FK5 (735 stars), from the catalogue of remainingSup stars (RSup, 732 stars), and from the faint extension of the FK5(1805 stars). From the 3272 stars in Part III, we have selected 1928objects as "astrometrically excellent stars", since their instantaneousproper motions and their mean (time-averaged) ones do not differsignificantly. Hence most of the astrometrically excellent stars arewell-behaving "single-star candidates" with good astrometric data. Thesestars are most suited for high-precision astrometry. On the other hand,354 of the stars in Part III are Δμ binaries in the sense ofWielen et al. (1999). Many of them are newly discovered probablebinaries with no other hitherto known indication of binarity. The FK6gives, besides the classical "single-star mode" solutions (SI mode),other solutions which take into account the fact that hidden astrometricbinaries among "apparently single-stars" introduce sizable "cosmicerrors" into the quasi-instantaneously measured HIPPARCOS proper motionsand positions. The FK6 gives, in addition to the SI mode, the "long-termprediction (LTP) mode" and the "short-term prediction (STP) mode". TheseLTP and STP modes are on average the most precise solutions forapparently single stars, depending on the epoch difference with respectto the HIPPARCOS epoch of about 1991. The typical mean error of anFK6(III) proper motion in the single-star mode is 0.59 mas/year. This isa factor of 1.34 better than the typical HIPPARCOS errors for thesestars of 0.79 mas/year. In the long-term prediction mode, in whichcosmic errors are taken into account, the FK6(III) proper motions have atypical mean error of 0.93 mas/year, which is by a factor of about 2better than the corresponding error for the HIPPARCOS values of 1.83mas/year (cosmic errors included).
| 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
| A Consistency Test of Spectroscopic Gravities for Late-Type Stars
Chemical analyses of late-type stars are usually carried out followingthe classical recipe: LTE line formation and homogeneous,plane-parallel, flux-constant, and LTE model atmospheres. We reviewdifferent results in the literature that have suggested significantinconsistencies in the spectroscopic analyses, pointing out thedifficulties in deriving independent estimates of the stellarfundamental parameters and hence, detecting systematic errors. Thetrigonometric parallaxes measured by the Hipparcos mission provideaccurate appraisals of the stellar surface gravity for nearby stars,which are used here to check the gravities obtained from thephotospheric iron ionization balance. We find an approximate agreementfor stars in the metallicity range -1.0<=[Fe/H]<=0, but thecomparison shows that the differences between the spectroscopic andtrigonometric gravities decrease toward lower metallicities for moremetal-deficient dwarfs (-2.5<=[Fe/H]<=-1.0), which casts a shadowupon the abundance analyses for extreme metal-poor stars that make useof the ionization equilibrium to constrain the gravity. The comparisonwith the strong-line gravities derived by Edvardsson and Fuhrmannconfirms that this method provide systematically larger gravities thanthe ionization balance. The strong-line gravities get closer to thephysical ones for the stars analyzed by Fuhrmann, but they are evenfurther away than the iron ionization gravities for the stars of lowergravities in Edvardsson's sample. The confrontation of the deviations ofthe iron ionization gravities in metal-poor stars, reported here withdepartures from the excitation balance found in the literature, showthat they are likely to be induced by the same physical mechanism.
| The origin of carbon, investigated by spectral analysis of solar-type stars in the Galactic Disk
Abundance analysis of carbon has been performed in a sample of 80 late Fand early G type dwarf stars in the metallicity range{-1.06<=[Fe/H]<=0.26} using the forbidden [C i] line at 8727Angstroms. This line is presumably less sensitive to temperature,atmospheric structure and departures from LTE than alternative carboncriteria. We find that {[C/Fe]} decreases slowly with increasing{[Fe/H]} with an overall slope of -0.17+/-0.03. Our results areconsistent with carbon enrichment by superwinds of metal-rich massivestars but inconsistent with a main origin of carbon in low-mass stars.This follows in particular from a comparison between the relation of{[C/O]} with metallicity for the Galactic stars and the correspondingrelation observed for dwarf irregular galaxies. The significance ofintermediate-mass stars for the production of carbon in the Galaxy isstill somewhat unclear. Based on observations carried out at theEuropean Southern Observatory, La Silla, Chile.
| The ROSAT all-sky survey catalogue of optically bright main-sequence stars and subgiant stars
We present X-ray data for all main-sequence and subgiant stars ofspectral types A, F, G, and K and luminosity classes IV and V listed inthe Bright Star Catalogue that have been detected as X-ray sources inthe ROSAT all-sky survey; several stars without luminosity class arealso included. The catalogue contains 980 entries yielding an averagedetection rate of 32 percent. In addition to count rates, sourcedetection parameters, hardness ratios, and X-ray fluxes we also listX-ray luminosities derived from Hipparcos parallaxes. The catalogue isalso available in electronic form via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Revised ages for stars in the solar neighbourhood
New ages are computed for the stars from the Edvardsson et al. (1993)data set. The revised values are systematically larger toward older ages(t>4 Gyr), while they are slightly lower for t<4 Gyr. A similar,but considerably smaller trend is present when the ages are computedwith the distances based on Hipparcos parallaxes. The resultingage-metallicity relation has a small, but distinct slope of ~ em0.07dex/Gyr. Tables 3\to8 are only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or WWW at URLhttp://cdsweb.u-strasbg.fr/Abstract.html
| The Tokyo PMC catalog 90-93: Catalog of positions of 6649 stars observed in 1990 through 1993 with Tokyo photoelectric meridian circle
The sixth annual catalog of the Tokyo Photoelectric Meridian Circle(PMC) is presented for 6649 stars which were observed at least two timesin January 1990 through March 1993. The mean positions of the starsobserved are given in the catalog at the corresponding mean epochs ofobservations of individual stars. The coordinates of the catalog arebased on the FK5 system, and referred to the equinox and equator ofJ2000.0. The mean local deviations of the observed positions from theFK5 catalog positions are constructed for the basic FK5 stars to comparewith those of the Tokyo PMC Catalog 89 and preliminary Hipparcos resultsof H30.
| The Angular Momentum of Main Sequence Stars and Its Relation to Stellar Activity
Rotational velocities are reported for intermediate-mass main sequencestars it the field. The measurements are based on new, high S/N CCDspectra from the Coudé Feed Telescope of the Kitt Peak NationalObservatory. We analyze these rotation rates for a dependence on bothmass and age. We compare the average rotation speeds of the field starswith mean velocities for young stars in Orion, the Alpha Persei cluster,the Pleiades, and the Hyades. The average rotation speeds of stars moremassive than $\sim1.6$ \msun\experience little or no change during theevolutionary lifetimes of these stars on the zero age main sequence orwithin the main sequence band. Less massive stars in the range betwee n1.6\msun\ and 1.3\msun\ also show little decline in mean rotation ratewhile they are on the main sequence, and at most a factor of 2 decreasein velocity as they evolve off the main sequence. The {\it e}-foldingtime for the loss of angular momentum b y the latter group of stars isat least 1--2 billion years. This inferred characteristic time scale forspindown is far longer than the established rotational braking time forsolar-type stars with masses below $\sim1.3$ \msun. We conclude from acomparison of the trends in rotation with trends in chromospheric andcoronal activity that the overall decline in mean rotation speed alongthe main sequence, from $\sim2$ \msun\ down to $\sim1.3$ \msun, isimposed during the pre-main sequence phase of evolution, and that thispattern changes little thereafter while the star resides on the mainsequence. The magnetic activity implicated in the rotational spindown ofthe Sun and of similar stars during their main sequence lifetimes mus ttherefore play only a minor role in determining the rotation rates ofthe intermediate mass stars, either because a solar-like dynamo is weakor absent, or else the geometry of the magnetic field is appreciablyless effective in removing angular momentu m from these stars. (SECTION:Stars)
| Infrared spectroscopy of the long-period polar RX J0515.6+0105
We present K-band (1.81-2.44 μm) spectroscopy of the 7.98-h orbitalperiod polar RX J0515.6+0105. Spectra obtained around orbital phase 0.5reveal strong emission lines of neutral hydrogen and helium from theaccretion stream. No obvious spectral features from the secondary starare detected: the K-band emission is dominated instead by cyclotronradiation from the accretion region. We find that the slope of thecyclotron spectrum is consistent with a magnetic field strength of 60MG, in agreement with previous optical studies and with the results fromour modelling of previous white-light polarimetry. We estimate that thesecondary contributes less than ~20 per cent of the infrared flux,implying a distance greater than ~1500 pc. With this result, we estimatethe mass transfer rate to be greater than ~1.0x10^17 g s^-1. We showthat it is plausible that the system is synchronized with the derivedvalues of the mass transfer rate and with a primary magnetic fieldstrength of 60 MG.
| The Abundance of CN. Calcium and Heavy Elements in High Velocity Stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114..825E&db_key=AST
| 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
| Magnetic Field and Rotation in Lower Main-Sequence Stars: an Empirical Time-dependent Magnetic Bode's Relation?
We find a significant correlation between the magnetic and rotationalmoments for a sample of 112 lower main-sequence stars. The rotationalmoment is calculated from measurements of the rotation period in most ofthe stars (not from the projected rotational velocity inferred fromDoppler broadening). The magnetic moment is computed from a database ofhomogeneous measurements of the mean level of Ca II H and K emissionfluxes sampled for most of the stars over an interval of 25 yr. Theslope connecting the logarithm of the magnetic moment and the logarithmof the rotational moment is about +0.5--0.6, with a Pearson correlationcoefficient of about +0.9. The scatter of points from the mean relationhas a component that is natural and caused by decade-long surfacevariability.
| The photoelectric astrolabe catalogue of Yunnan Observatory (YPAC).
The positions of 53 FK5, 70 FK5 Extension and 486 GC stars are given forthe equator and equinox J2000.0 and for the mean observation epoch ofeach star. They are determined with the photoelectric astrolabe ofYunnan Observatory. The internal mean errors in right ascension anddeclination are +/- 0.046" and +/- 0.059", respectively. The meanobservation epoch is 1989.51.
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Pozíciós és asztrometriai adatok
| Csillagkép: | Orion |
| Rektaszcenzió: | 05h11m19.20s |
| Deklináció: | -02°29'27.0" |
| Vizuális fényesség: | 5.9 |
| Távolság: | 38.402 parszek |
| RA sajátmozgás: | 81.5 |
| Dec sajátmozgás: | 1.9 |
| B-T magnitude: | 6.433 |
| V-T magnitude: | 5.945 |
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