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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
| X-ray source populations in the Galactic plane
We present the first results from the XMM-Newton Galactic Plane Survey(XGPS). In the first phase of the programme, 22 pointings were used tocover a region of approximately 3 deg2 between 19° and22° in Galactic longitude and +/-0.6° in latitude. In total wehave resolved over 400 point X-ray sources, at >= 5?significance, down to a flux limit of ~2 × 10-14 ergs-1cm-2 (2-10 keV). The sources exhibit a verywide range of spectral hardness, with interstellar absorption identifiedas a major influence. The source populations detected in the soft (0.4-2keV) band and hard (2-6 keV) band show surprisingly little overlap. Themajority of the soft sources appear to be associated with relativelynearby stars with active stellar coronae, judging from their highcoincidence with bright stellar counterparts.The combination of the XGPS measurements in the hard X-ray band with theresults from earlier surveys carried out by ASCA and Chandra reveals theform of the low-latitude X-ray source counts over 4 decades of flux. Itappears that extragalactic sources dominate below ~10-13 ergs-1cm-2 (2-10 keV), with a predominantly Galacticsource population present above this flux threshold. The nature of thefaint Galactic population observed by XMM-Newton remains uncertain,although cataclysmic variables and RS CVn systems may contributesubstantially. XMM-Newton observes an enhanced surface brightness in theGalactic plane in the 2-6 keV band associated with Galactic ridge X-rayemission (GRXE). The integrated contribution of Galactic sources plusthe breakthrough of extragalactic signal accounts for up to 20 per centof the observed surface brightness. The XGPS results are consistent withthe picture suggested from a deep Chandra observation in the Galacticplane, namely that the bulk of the GRXE is truly diffuse.
| 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
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Osservazione e dati astrometrici
| Costellazione: | Scudo |
| Ascensione retta: | 18h30m32.26s |
| Declinazione: | -10°51'50.2" |
| Magnitudine apparente: | 7.957 |
| Distanza: | 121.359 parsec |
| Moto proprio RA: | -1.3 |
| Moto proprio Dec: | 19.1 |
| B-T magnitude: | 8.519 |
| V-T magnitude: | 8.004 |
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INHABITED SKY
