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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
| [NE II] 12.8 Micron Images of Four Galactic Ultracompact H II Regions: Ionized Neon Abundance as a Tracer of the Ionizing Stars
We present the results of ground-based imaging spectroscopy of the [NeII] 12.8 μm line emitted from the ultracompact (UC) H II regionsW51d, G45.12+0.13, G35.20-1.74, and Monoceros R2, with 2" spatialresolution. We found that the overall distribution of the [Ne II]emission is generally in good agreement with the radio (5 or 15 GHz) VLAdistribution for each source. The Ne+ abundance([Ne+/H+]) distributions are also derived from the[Ne II] and the radio maps. As for G45.12+0.13 and W51d, theNe+ abundance decreases steeply from the outer part of themap toward the radio peak. On the other hand, the Ne+abundance distributions of G35.20-1.74 and Mon R2 appear rather uniform.These results can be interpreted by the variation of ionizing structuresof neon, which is determined primarily by the spectral type of theionizing stars. We have evaluated the effective temperature of theionizing star by comparing the Ne+ abundance averaged overthe whole observed region with that calculated by H II region modelsbased on recent non-LTE stellar atmosphere models:39,100+1100-500 K (O7.5 V-O8 V) for W51d; 37,200+1000-700 K (O8 V-O8.5 V) for G45.12+0.1335,000-37,600+1500-600 K (O8 V-O9 V) forG35.20-1.74 and <=34,000 K (<=B0 V) for Mon R2. These effectivetemperatures are consistent with those inferred from the observedNe+ abundance distributions.
| Infrared images of Monoceros R2 IRS 3 - Evidence for a circumstellar disk
Diffraction-limited IR images of the protostellar system Mon R2 IRS 3reveal a bright conical nebula which extends about 0.5 arcsec south fromthe southern component of the previously known star pair. The brightnebula is probably dust scattering the starlight which emerges along thepolar axis of a large (greater than 500 AU) circumstellar disk. Weestimate a lower limit to the disk mass of 3 X 10 exp -2 solar masses. Afaint, previously unknown pointlike source lies 0.37 arcsec east of thenorthern star.
| SAO stars with infrared excess in the IRAS Point Source Catalog
We have undertaken a search for SAO stars with infrared excess in theIRAS Point Source Catalog. In contrast to previous searches, the entireIRAS (12)-(25)-(60) color-color diagram was used. This selection yieldeda sample of 462 stars, of which a significant number are stars withcircumstellar material. The stars selected can be identified aspre-main-sequence stars, Be stars, protoplanetary systems, post-AGBstars, etc. A number of objects are (visual) binary stars.Characteristic temperatures and IR excesses are calculated and theirrelations to spectral type are investigated.
| MK classifications for F-and G-type stars. 3.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1974AJ.....79..682H&db_key=AST
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Besorolás csoportokba:
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Pozíciós és asztrometriai adatok
| Csillagkép: | Egyszarvú |
| Rektaszcenzió: | 06h08m47.70s |
| Deklináció: | -06°49'17.0" |
| Vizuális fényesség: | 6.469 |
| Távolság: | 111.359 parszek |
| RA sajátmozgás: | -30.8 |
| Dec sajátmozgás: | 7.4 |
| B-T magnitude: | 7.562 |
| V-T magnitude: | 6.56 |
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INHABITED SKY
