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Kinematics, ages and metallicities for F- and G-type stars in the solar neighbourhood
A new metallicity distribution and an age-metallicity relation arepresented for 437 nearby F and G turn-off and sub-giant stars selectedfrom radial velocity data of Nidever et al. Photometric metallicitiesare derived from uvby- Hβ photometry, and the stellar ages from theisochrones of Bergbusch & VandenBerg as transformed to uvbyphotometry using the methods of Clem et al.The X (stellar population) criterion of Schuster et al., which combinesboth kinematic and metallicity information, provides 22 thick-discstars. σW= 32 +/- 5 km s-1,= 154 +/- 6 km s-1 and<[M/H]>=-0.55 +/- 0.03 dex for these thick-disc stars, which is inagreement with values from previous studies of the thick disc.α-element abundances which are available for some of thesethick-disc stars show the typical α-element signatures of thethick disc, supporting the classification procedure based on the Xcriterion.Both the scatter in metallicity at a given age and the presence of old,metal-rich stars in the age-metallicity relation make it difficult todecide whether or not an age-metallicity relation exists for the olderthin-disc stars. For ages greater than 3 Gyr, our results agree with theother recent studies that there is almost no correlation between age andmetallicity, Δ([M/Fe])/Δ(age) =-0.01 +/- 0.005 dexGyr-1. For the 22 thick-disc stars there is a range in agesof 7-8 Gyr, but again almost no correlation between age and metallicity.For the subset of main-sequence stars with extra-solar planets, theage-metallicity relation is very similar to that of the total sample,very flat, the main difference being that these stars are mostlymetal-rich, [M/H]>~-0.2 dex. However, two of these stars have[M/H]~-0.6 dex and have been classified as thick-disc stars. As for thetotal sample, the range in ages for these stars with extra-solarplanetary systems is considerable with a nearly uniform distributionover 3 <~ age <~ 13 Gyr.
| 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.
| Chromospheric Ca II Emission in Nearby F, G, K, and M Stars
We present chromospheric Ca II H and K activity measurements, rotationperiods, and ages for ~1200 F, G, K, and M type main-sequence stars from~18,000 archival spectra taken at Keck and Lick Observatories as a partof the California and Carnegie Planet Search Project. We have calibratedour chromospheric S-values against the Mount Wilson chromosphericactivity data. From these measurements we have calculated medianactivity levels and derived R'HK, stellar ages,and rotation periods from general parameterizations for 1228 stars,~1000 of which have no previously published S-values. We also presentprecise time series of activity measurements for these stars.Based on observations obtained at Lick Observatory, which is operated bythe University of California, and on observations obtained at the W. M.Keck Observatory, which is operated jointly by the University ofCalifornia and the California Institute of Technology. The KeckObservatory was made possible by the generous financial support of theW. M. Keck Foundation.
| 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
| The Nature of Overluminous F Stars Observed in a Radial-Velocity Survey
We have conducted a radial-velocity survey of bright (V<9),overluminous, F stars within 80 pc. The criterion of overluminosity isΔMc0=Mc0-MV>=0.5,where MV is the absolute magnitude based on the Hipparcosparallax and Mc0 is the absolute magnitude fromuvby photometry. For F stars, overluminosity at a level ofΔMc0>0.15 has been argued to beindicative of the presence of a bright companion, so many of theoverluminous ``single'' F stars are expected to be, in fact, binarieswith comparably bright components. Therefore, the main goals of thesurvey have been to gain insight into the nature of overluminous F starsand to test specifically the hypothesis of the duplicity of overluminousF stars by searching for previously unrecognized binary stars amongthem. Other goals of this project included the determination, whereverpossible, of the orbits of the binaries discovered as a result of thesurvey and comparing the properties of the binaries with those of thevisually single stars with constant radial velocity. The program listcomprised 111 stars that appear in the Hipparcos catalog as single, plusseven members of multiple systems whose components have individualentries in the catalog.Of the total of 118 stars selected, the radial velocities of 77 havebeen measured with the Cambridge CORAVEL in the present survey. Amongthe remainder, six have not allowed us to determine their radialvelocities because of the weakness or lack of a ``dip'' in theirradial-velocity traces, and one was optically inaccessible to thetelescope. All the rest proved to be sufficiently well known alreadyeither as binary or as constant-radial-velocity (CRV) stars. The surveydiscovered 25 new binary systems, not counting two that were notgenerally known as such but were already under observation by R. F. G.and two that were discovered by Hipparcos to show eclipses but had neverbeen recognized as SBs. With the previously known binaries, there is atotal of 61 definite plus three probable binaries out of a total of 111stars upon which we can adjudicate-a binary fraction of ~58%, justdouble the ~29% found in a sample of randomly selected F stars byNordström et al. (1997). Of the binaries, 52 are SB2 and 12 areSB1. Orbits (some of them still rather preliminary) have been determinedfor the first time for 28 binaries, 21 of which are SB2.Comparison of the CRV stars (a total of 47) with the SB2 binaries hasshown that the two groups have different kinematics. The differenceimplies that on average the CRV stars are 3 to 4 Gyr older than theSB2s, although several of the CRVs appear to be very young. At the sametime the SB2 stars turn out to have about the same kinematics, hence thesame average age, as both binary and normal single F stars from acontrol sample drawn from the Hipparcos catalog. The much older age ofthe bulk of the overluminous CRV F stars may be indicative of anomalousstellar evolution that results in anomalously long main-sequencelifetimes for those stars. The SB1 stars appear to be closer to the CRVsthan to the SB2s and are probably also very old. The properties of the``no-dip'' stars suggest very young age; some of the stars are probablypre-main-sequence (PMS). A few PMS candidates have been identified alsoamong the CRV stars. Thus, overluminous F stars comprising our sampleappear to consist of three distinct groups: mostly young SB2 binarieswith comparably bright components, mostly very old CRV and SB1 stars,and very young no-dip stars.
| Improved Astrometry and Photometry for the Luyten Catalog. II. Faint Stars and the Revised Catalog
We complete construction of a catalog containing improved astrometry andnew optical/infrared photometry for the vast majority of NLTT starslying in the overlap of regions covered by POSS I and by the secondincremental Two Micron All Sky Survey (2MASS) release, approximately 44%of the sky. The epoch 2000 positions are typically accurate to 130 mas,the proper motions to 5.5 mas yr-1, and the V-J colors to0.25 mag. Relative proper motions of binary components are measured to 3mas yr-1. The false-identification rate is ~1% for11<~V<~18 and substantially less at brighter magnitudes. Theseimprovements permit the construction of a reduced proper-motion diagramthat, for the first time, allows one to classify NLTT stars intomain-sequence (MS) stars, subdwarfs (SDs), and white dwarfs (WDs). We inturn use this diagram to analyze the properties of both our catalog andthe NLTT catalog on which it is based. In sharp contrast to popularbelief, we find that NLTT incompleteness in the plane is almostcompletely concentrated in MS stars, and that SDs and WDs are detectedalmost uniformly over the sky δ>-33deg. Our catalogwill therefore provide a powerful tool to probe these populationsstatistically, as well as to reliably identify individual SDs and WDs.
| Radial Velocities for 889 Late-Type Stars
We report radial velocities for 844 FGKM-type main-sequence and subgiantstars and 45 K giants, most of which had either low-precision velocitymeasurements or none at all. These velocities differ from the standardstars of Udry et al. by 0.035 km s-1 (rms) for the 26 FGKstandard stars in common. The zero point of our velocities differs fromthat of Udry et al.: =+0.053km s-1. Thus, these new velocities agree with the best knownstandard stars both in precision and zero point, to well within 0.1 kms-1. Nonetheless, both these velocities and the standardssuffer from three sources of systematic error, namely, convectiveblueshift, gravitational redshift, and spectral type mismatch of thereference spectrum. These systematic errors are here forced to be zerofor G2 V stars by using the Sun as reference, with Vesta and day sky asproxies. But for spectral types departing from solar, the systematicerrors reach 0.3 km s-1 in the F and K stars and 0.4 kms-1 in M dwarfs. Multiple spectra were obtained for all 889stars during 4 years, and 782 of them exhibit velocity scatter less than0.1 km s-1. These stars may serve as radial velocitystandards if they remain constant in velocity. We found 11 newspectroscopic binaries and report orbital parameters for them. Based onobservations obtained at the W. M. Keck Observatory, which is operatedjointly by the University of California and the California Institute ofTechnology, and on observations obtained at the Lick Observatory, whichis operated by the University of California.
| 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.
| 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
| All-sky Stromgren photometry of speckle binary stars
All-sky Stromgren photometric observations were obtained for 303 specklebinaries. Most stars were in the range of V = 5-8. These data, whencombined with ratios of intensities from the CHARA speckle photometryprogram, will allow the determination of photometric indices for theindividual components of binary stars with separations as small as 0.05arcsec. These photometric indices will complement the stellar massesfrom the speckle interferometry observations to provide a much improvedmass-luminosity relationship.
| ICCD speckle observations of binary stars. IV - Measurements during 1986-1988 from the Kitt Peak 4 M telescope
One thousand five hundred and fifty measurements of 1006 binary starsystems observed mostly during 1986 through mid-1988 by means of speckleinterferometry with the KPNO 4-m telescope are presented. Twenty-onesystems are directly resolved for the first time, including newcomponents to the cool supergiant Alpha Her A and the Pleiades shellstar Pleione. A continuing survey of The Bright Star Catalogue yieldedeight new binaries from 293 bright stars observed. Corrections tospeckle measures from the GSU/CHARA ICCD speckle camera previouslypublished are presented and discussed.
| New UBVRI photometry for 900 supergiants
A description is presented of the results obtained in connection with asystematic program of supergiant photometry on the Johnson UBVRI system.During the eight years after the start of the program, almost 1000 starshave been observed, about 400 three or more times each. The originalselection of stars used the spectral type catalog of Jaschek et al.(1964) to choose supergiants. Since observations were possible from bothChile and Canada, no declination limits were imposed, and no particularselection criteria were imposed other than to eliminate carbon stars.These are so red as to require enormous extrapolations of thetransformation equations.
| MK classifications for F-and G-type stars. 3.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1974AJ.....79..682H&db_key=AST
| A catalogue of four-color photometry of late F-type stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1969AJ.....74..705P&db_key=AST
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| Csillagkép: | Halak |
| Rektaszcenzió: | 23h15m40.27s |
| Deklináció: | +01°18'29.7" |
| Vizuális fényesség: | 6.768 |
| Távolság: | 44.425 parszek |
| RA sajátmozgás: | 194.5 |
| Dec sajátmozgás: | -46.6 |
| B-T magnitude: | 7.394 |
| V-T magnitude: | 6.82 |
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