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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.
| 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
| Linear polarization and molecular filamentary clouds
We have carried out deep CCD polarimetry in the I band in selectedfields in three filamentary, molecular clouds: the L1400 complex, L204,and MBM25, at galactic latitudes 4degr , 21degr , and 31degr ,respectively. I magnitudes and the degree and direction of linearpolarization were measured with satisfactory accuracies for 387 starsdown to I=19.5. Typical uncertainties of the degree and angle ofpolarization are ΔP{~}0.5% and Δθ{~}10degr . We alsoderived extinctions from star counts in and around the observed fields.In the L1400 complex we imaged a 48 arcmin(2) field in the H and Kbands, providing independent measures of extinction based on the E(H-K)colour excess. Our measurements show that the patterns of polarizationare remarkably smooth over the fields studied, particularly in the L1400complex. There is no indication of any statistically significantdifference in polarization angle and degree between obscured andnon-obscured regions. MBM25, with the lowest levels of extinction andpolarization, shows some anomalies in the polarization vectors, but thestatistics is here less good. Our method opens the possibility to studysmall-scale irregularities in the polarization pattern on angular scalesdown to a few arcseconds. Comparing the extinction A_V and P/A_V in thefield observed in the H and K bands we find that P/A_V can attain highvalues (close to the P=3 A_V relation) only for small values of A_V.Modelling the stellar content along the line of sight reveals that we,for magnitudes around I=19, sample stars at very large distances behindthe clouds. Our general conclusion is that the interstellar filamentscontribute very little to the polarization measured. This is in linewith recent results obtained for other cloud regions comprising lessdetailed spatial scale and a smaller depth in brightness. Using asemi-empirical version of the Davis-Greenstein mechanism we havecalculated the polarization for simple models of the three cloudsstudied, and find that it is considerably smaller than the typicalbackground polarization, a result in consonance with the polarimetricmeasurements. For MBM25 we derive a new distance of ~ 145 pc fromHipparcos parallaxes of two stars surrounded by bright nebulosities, onthe assumption that the stars are physically associated with the cloud.Based on observations made with the Nordic Optical Telescope, operatedon the island of La Palma jointly by Denmark, Finland, Iceland, Norway,and Sweden, in the Spanish Observatorio del Roque de los Muchachos ofthe Instituto de Astrofisica de Canarias.
| 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
| Radial-velocity measurements. V - Ground support of the HIPPARCOS satellite observation program
The paper presents data on 1070 radial velocity measurements of starsdistributed in 39 fields measuring 4 deg x 4 deg. The PPO series ofFehrenbach et al. (1987) and Duflot et al. (1990) is continued using theFehrenbach objective prism method.
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Группы:
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Наблюдательные данные и астрометрия
| Созвездие: | Жираф |
| Прямое восхождение: | 04h28m54.30s |
| Склонение: | +55°00'01.7" |
| Видимая звёздная величина: | 7.672 |
| Расстояние: | 87.719 парсек |
| Собственное движение RA: | -33 |
| Собственное движение Dec: | -19.6 |
| B-T magnitude: | 8.329 |
| V-T magnitude: | 7.727 |
Каталоги и обозначения:
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