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The Geneva-Copenhagen survey of the solar neighbourhood. III. Improved distances, ages, and kinematics
Context: Ages, chemical compositions, velocity vectors, and Galacticorbits for stars in the solar neighbourhood are fundamental test datafor models of Galactic evolution. The Geneva-Copenhagen Survey of theSolar Neighbourhood (Nordström et al. 2004; GCS), amagnitude-complete, kinematically unbiased sample of 16 682 nearby F andG dwarfs, is the largest available sample with complete data for starswith ages spanning that of the disk. Aims: We aim to improve theaccuracy of the GCS data by implementing the recent revision of theHipparcos parallaxes. Methods: The new parallaxes yield improvedastrometric distances for 12 506 stars in the GCS. We also use theparallaxes to verify the distance calibration for uvby? photometryby Holmberg et al. (2007, A&A, 475, 519; GCS II). We add newselection criteria to exclude evolved cool stars giving unreliableresults and derive distances for 3580 stars with large parallax errorsor not observed by Hipparcos. We also check the GCS II scales of T_effand [Fe/H] and find no need for change. Results: Introducing thenew distances, we recompute MV for 16 086 stars, and U, V, W,and Galactic orbital parameters for the 13 520 stars that also haveradial-velocity measurements. We also recompute stellar ages from thePadova stellar evolution models used in GCS I-II, using the new valuesof M_V, and compare them with ages from the Yale-Yonsei andVictoria-Regina models. Finally, we compare the observed age-velocityrelation in W with three simulated disk heating scenarios to show thepotential of the data. Conclusions: With these revisions, thebasic data for the GCS stars should now be as reliable as is possiblewith existing techniques. Further improvement must await consolidationof the T_eff scale from angular diameters and fluxes, and the Gaiatrigonometric parallaxes. We discuss the conditions for improvingcomputed stellar ages from new input data, and for distinguishingdifferent disk heating scenarios from data sets of the size andprecision of the GCS.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/501/941
| 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
| Fe II/Mg II Emission-Line Ratio in High-Redshift Quasars
We present results of the analysis of near-infrared spectroscopicobservations of six high-redshift quasars (z>~4), emphasizing themeasurement of the ultraviolet Fe II/Mg II emission-line strength toestimate the beginning of intense star formation in the early universe.To investigate the evolution of the Fe II/Mg II ratio over a wider rangein cosmic time, we measured this ratio for composite quasar spectra thatcover a redshift range 0<~z<~5 with nearly constant luminosity, aswell as for those that span ~6 orders of magnitude in luminosity. Adetailed comparison of the high-redshift quasar spectra with those oflow-redshift quasars with comparable luminosity shows essentially thesame Fe II/Mg II emission ratios and very similar continuum and linespectral properties, i.e., a lack of evolution of the relativeiron-to-magnesium abundance of the gas in bright quasars since z~=5.Current nucleosynthesis and stellar evolution models predict thatα-elements such as magnesium are produced in massive stars endingin Type II supernovae, while iron is formed predominantly in Type Iasupernovae with intermediate-mass progenitors. This results in an ironenrichment delay of ~0.2-0.6 Gyr. We conclude that intense starformation activity in the host galaxies of z>~4 quasars must havestarted already at an epoch corresponding to zf~=6-9, whenthe age of the universe was ~0.5 Gyr (H0=72 km s-1Mpc-1, ΩM=0.3,ΩΛ=0.7). This epoch corresponds well to thereionization era of the universe.Based on observations collected at the Cerro Tololo Inter-AmericanObservatory, Chile, at the European Southern Observatory, Paranal,Chile, and the W. M. Keck Observatory, Hawaii.
| High-Redshift Quasars and Star Formation in the Early Universe
In order to derive information on the star formation history in theearly universe, we observed six high-redshift (z~=3.4) quasars in thenear-infrared to measure the relative iron and Mg II emission strengths.A detailed comparison of the resulting spectra with those oflow-redshift quasars show essentially the same Fe II /Mg II emissionratios and very similar continuum and line spectral properties,indicating a lack of evolution of the relative iron to magnesiumabundance of the gas since z~=3.4 in bright quasars. On the basis ofcurrent chemical evolution scenarios of galaxies, where magnesium isproduced in massive stars ending in Type II Supernovae (SNe II), whileiron is formed predominantly in SNe Ia with a delay of ~1 Gyr andassuming as cosmological parameters H0=72 km s-1Mpc-1, ΩM=0.3, andΩΛ=0.7, we conclude that major star formationactivity in the host galaxies of our z~=3.4 quasars must have startedalready at an epoch corresponding to zf~=10, when the age ofthe universe was less than 0.5 Gyr. Based on observations collected atthe European Southern Observatory, La Silla, Chile.
| A large, complete, volume-limited sample of G-type dwarfs. I. Completion of Stroemgren UVBY photometry
Four-colour photometry of potential dwarf stars of types G0 to K2,selected from the Michigan Spectral Catalogues (Vol. 1-3), has beencarried out. The results are presented in a catalogue containing 4247uvby observations of 3900 stars, all south of δ = -26deg. Theoverall internal rms errors of one observation (transformed to thestandard system) of a program star in the interval 8.5 < V < 10.5are 0.0044, 0.0021, 0.0039, and 0.0059, respectively, in V, b-y, m_1_ ,and c_1_. The purpose of the catalogue, combined with earliercatalogues, is to allow selection of a large, complete, volume-limitedsample of G- and K-type dwarfs, investigate their metallicitydistribution, and compare it to predictions of various models ofgalactic chemical evolution. Future papers in this series will discussthese subjects.
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משמש של הקבוצה הבאה
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | שעון |
| התרוממות ימנית: | 04h00m31.98s |
| סירוב: | -41°44'54.4" |
| גודל גלוי: | 8.383 |
| מרחק: | 54.054 פארסק |
| תנועה נכונה: | 68.9 |
| תנועה נכונה: | -2.7 |
| B-T magnitude: | 9.129 |
| V-T magnitude: | 8.445 |
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