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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.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| 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
| Radial velocities. Measurements of 2800 B2-F5 stars for HIPPARCOS
Radial velocities have been determined for a sample of 2930 B2-F5 stars,95% observed by the Hipparcos satellite in the north hemisphere and 80%without reliable radial velocity up to now. Observations were obtainedat the Observatoire de Haute Provence with a dispersion of 80Ä,mm(-1) with the aim of studying stellar and galactic dynamics.Radial velocities have been measured by correlation with templates ofthe same spectral class. The mean obtained precision is 3.0 km s(-1)with three observations. A new MK spectral classification is estimatedfor all stars. Based on observations made at the Haute ProvenceObservatory, France and on data from The Hipparcos Catalogue, ESA.Tables 4, 5 and 6 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr or viahttp://cdsweb.u-strasbg.fr/Abstract.htm
| Classification of Population II Stars in the Vilnius Photometric System. II. Results
The results of photometric classification of 848 true and suspectedPopulation II stars, some of which were found to belong to Population I,are presented. The stars were classified using a new calibrationdescribed in Paper I (Bartkevicius & Lazauskaite 1996). We combinethese results with our results from Paper I and discuss in greaterdetail the following groups of stars: UU Herculis-type stars and otherhigh-galactic-latitude supergiants, field red horizontal-branch stars,metal-deficient visual binaries, metal-deficient subgiants, stars fromthe Catalogue of Metal-deficient F--M Stars Classified Photometrically(MDPH; Bartkevicius 1993) and stars from one of the HIPPARCOS programs(Bartkevicius 1994a). It is confirmed that high galactic latitudesupergiants from the Bartaya (1979) catalog are giants or even dwarfs.Some stars, identified by Rose (1985) and Tautvaisiene (1996a) as fieldRHB stars, appear to be ordinary giants according to our classification.Some of the visual binaries studied can be considered as physical pairs.Quite a large fraction of stars from the MDPH catalog are found to havesolar metallicity. A number of new possible UU Herculis-type stars, RHBstars and metal-deficient subgiants are identified.
| The chemical composition of the field blue stragglers.
We present the results of the spectroscopic investigation of 15 galacticfield blue stragglers and one normal F-dwarf. The analysis has shown: 1)all stars are metal deficient. The mean value of [Fe/H] for 13 stars is-0.31+/-0.13 (two stars of our sample: HD54073 and HD88923 have probablystronger iron deficiency); 2) estimated (C/H) and (O/H) ratios are closeto the solar values (i.e. these elements are slightly enhanced withrespect to iron: [C/Fe]=~[O/Fe]=~0.3dex); 3) sodium and α-elementsin the field stragglers are slightly enhanced too. Only magnesium showsa practically solar ratio: [Mg/Fe]=~0; 4) from the iron group, Sc showssolar ratio [M/Fe]. Cr and Ni are slightly overabundant; 5) the rathergreat age of the investigated stars estimated from their metallicity isin the contradiction with their locations in the evolutionary diagram.This problem can be eliminated by assuming that field stragglers are oldobjects with delayed evolution (similarly to blue stragglers of stellarclusters); 6) one of the investigated stars HD35863 (T_eff_=6700K,logg=4.0) has a rather high lithium abundance (logA_Li_=2.94), not usualfor stars with such temperature.
| A survey of F-type stars
The results of a spectroscopic survey of 350 F-type stars at adispersion of 80 A/mm are presented. Twenty-two percent of the starsshow degree of metal line weakening; this result parallels that ofphotometric investigations in the uvby Beta system. The line weakeningparameter introduced correlates strongly with photometric indices andwith abundance anomalies established by theoreticians of stellaratmospheres. The classification can thus be used to easily select starswith underabundances stronger than a factor four with respect to thesun.
| Spectroscopic tests of photoelectric stellar classification of abnormal stars
Spectroscopic classification is obtained for 169 northern A5-G0 starspredicted by Olsen (1979, 1980) to have abnormal spectra on the basis ofStromgren four-color photometry. The success in identifying reddenedearly type stars was nearly 100 percent, for Am and early type weaklined stars about 75 percent, for stars above main sequence about 50percent, for composite spectra about 25 percent, and for Ap and LambdaBoo stars 0 percent. Thus photoelectric photometry is a successful firststep in discovering stars of the more extreme spectroscopicabnormalities.
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| Сазвежђа: | Велики медвед |
| Ректацензија: | 09h27m26.46s |
| Deклинација: | +41°36'00.2" |
| Apparent магнитуда: | 8.539 |
| Даљина: | 125 parsecs |
| Proper motion RA: | 17.4 |
| Proper motion Dec: | 0.3 |
| B-T magnitude: | 9.002 |
| V-T magnitude: | 8.578 |
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