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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
| Circumnuclear structure and kinematics in the active galaxy NGC 6951
A study is presented of the central structure and kinematics of thegalaxy NGC 6951, by means of broad band B{\arcminIJK} images and highresolution high dispersion longslit spectroscopy, together with archivalHST WFPC2 V and NICMOS2 J and H images. We find that there is littleongoing star formation inside the bar dominated region of the galaxy,except for the circumnuclear ring at 5 arcsec radius. There is someevidence that this star formation occurs in two modes, in bursts andcontinuously, along the ring and inwards, towards the nucleus. Theequivalent width of the Ca Ii triplet absorption lines show that, in themetal rich central region, the continuum is dominated by a population ofred supergiants, while red giants dominate outside. The gaseouskinematics along three slit position angles, and the comparison with thestellar kinematics, suggest the existence of a hierarchy of disks withindisks, whose dynamics are decoupled at the two inner Linblad resonances(ILR), that we find to be located at 180 pc and at 1100 pc. This issupported by the structure seen in the high resolution HST images. Thenucleus is spatially resolved in the emission line ratio [N Ii]/Hα, and in the FWHM of the emission lines, within a radius of1.5{\arcsec}, just inside the innermost ILR. Outside the iILR, thestellar CaT velocity profile is resolved into two different components,associated with the bar and the disk. Several results indicate that thisis a dynamically old system: the little ongoing star formation insidethe bar dominated part of the galaxy, the very large relative amount ofmolecular to total mass within the inner 6 arcsec radius, ~ 25%, and thegeometry of the circumnuclear ring that leads the stellar bar at aposition angle greater than 90°. It is thus possible that a nuclearbar has existed in NGC 6951 that drove the gas towards the nucleus, asin the bars within bars scenario, but that this bar has alreadydissolved by the gas accumulated within the circumnuclear region. Wediscuss the possibility that the kinematical component inside the iILRcould be due to a nuclear outflow produced by the combined effects of SNand SN remnants, or to a nuclear disk, as in the disk within diskscenario that we propose for the fueling of the AGN in NGC 6951. Basedon observations made with the 4.2m William Herschel Telescope operatedby the Isaac Newton Group, and the 2.6m Nordic Optical Telescopeoperated jointly by Denmark, Finland, Iceland, Norway, and Sweden, onthe island of La Palma in the Spanish Observatorio del Roque de losMuchachos of the Instituto de Astrofísica de Canarias. Also basedon observations made with the NASA/ESA Hubble Space Telescope, obtainedfrom the data archive at the ESA Space Telescope European CoordinatingFacility.
| 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
| 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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משמש של הקבוצה הבאה
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | פגסוס |
| התרוממות ימנית: | 21h55m51.96s |
| סירוב: | +26°24'11.7" |
| גודל גלוי: | 8.371 |
| מרחק: | 180.505 פארסק |
| תנועה נכונה: | 25.5 |
| תנועה נכונה: | -52.4 |
| B-T magnitude: | 9.111 |
| V-T magnitude: | 8.433 |
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