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Metallicity in the solar neighborhood out to 60 pc
We present an overview and early results on a continuing large-scaleproject to analyze spectra of solar-types stars in the solarneighborhood out to 60 pc. Physical parameters and initial metallicityestimates for 4043 stars have been derived. We have developed computerprograms to help automate the process from synthetic spectrum generationto metallicity determination. Initial metallicity estimates for 3613stars have been calculated based on low resolution spectra. Results fromthis project will be useful in answering questions about chemicalhomogeneity in the solar neighborhood, developing age–metallicityrelationships, and in identifying candidate stars for futureplanet-hunting projects.
| 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.
| Keck HIRES Spectroscopy of Four Candidate Solar Twins
We use high signal-to-noise ratio, high-resolution Keck HIRESspectroscopy of four solar twin candidates (HIP 71813, 76114, 77718, and78399) pulled from our Hipparcos-based Ca II H and K survey to carry outparameter and abundance analyses of these objects. Our spectroscopicTeff estimates are ~100 K hotter than the photometric scale of therecent Geneva-Copenhagen survey; several lines of evidence suggest thephotometric temperatures are too cool at solar Teff. At the same time,our abundances for the three solar twin candidates included in theGeneva-Copenhagen survey are in outstanding agreement with thephotometric metallicities; there is no sign of the anomalously lowphotometric metallicities derived for some late-G UMa group and Hyadesdwarfs. A first radial velocity determination is made for HIP 78399 andUVW kinematics derived for all stars. HIP 71813 appears to be akinematic member of the Wolf 630 moving group (a structure apparentlyreidentified in a recent analysis of late-type Hipparcos stars), but itsmetallicity is 0.1 dex higher than the most recent estimate of thisgroup's metallicity. While certainly solar-type stars, HIP 76114 and77718 are a few percent less massive, significantly older, andmetal-poor compared to the Sun; they are neither good solar twincandidates nor solar analogs providing a look at the Sun at some otherpoint in its evolution. HIP 71813 appears to be an excellent solaranalog of ~8 Gyr age. Our results for HIP 78399 suggest the promise ofthis star as a solar twin may be equivalent to the ``closest ever solartwin,'' HR 6060; follow-up study of this star is encouraged.
| 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.
| 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
| MK classifications for F and G-type stars. I.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1969AJ.....74..916H&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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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | נחש |
| התרוממות ימנית: | 15h52m00.55s |
| סירוב: | +15°14'09.3" |
| גודל גלוי: | 7.311 |
| מרחק: | 31.447 פארסק |
| תנועה נכונה: | -60.5 |
| תנועה נכונה: | -126.4 |
| B-T magnitude: | 8.049 |
| V-T magnitude: | 7.372 |
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