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Analysis of old very metal rich stars in the solar neighbourhood
Context. A sample of mostly old metal-rich dwarf and turn-off stars withhigh eccentricity and low maximum height above the Galactic plane hasbeen identified. From their kinematics, it was suggested that the innerdisk is their most probable birthplace. Their chemical imprints maytherefore reveal important information about the formation and evolutionof the still poorly understood inner disk. Aims: To probe theformation history of these stellar populations, a detailed analysis of asample of very metal-rich stars is carried out. We derive themetallicities, abundances of ? elements, ages, and Galacticorbits. Methods: The analysis of 71 metal-rich stars is based onoptical high-resolution échelle spectra obtained with the FEROSspectrograph at the ESO 1.52-m Telescope at La Silla, Chile. Themetallicities and abundances of C, O, Mg, Si, Ca, and Ti were derivedbased on LTE detailed analysis, employing the MARCS model atmospheres. Results: We confirm the high metallicity of these stars reachingup to [Fe i/H] = 0.58, and the sample of metal-rich dwarfs can bekinematically subclassified in samples of thick disk, thin disk, andintermediate stellar populations. All sample stars show solar ?-Feratios, and most of them are old and still quite metal rich. The orbitssuggest that the thin disk, thick disk and intermediate populations wereformed at Galactocentric distances of ~8 kpc, ~6 kpc, and ~7 kpc,respectively. The mean maximum height of the thick disk subsample ofZmax ~ 380 pc, is lower than for typical thick disk stars. Acomparison of ?-element abundances of the sample stars with bulgestars shows that the oxygen is compatible with a bulge or inner thickdisk origin. Our results suggest that models of radial mixing anddynamical effects of the bar and bar/spiral arms might explain thepresence of these old metal-rich dwarf stars in the solar neighbourhood.Observations collected at the European Southern Observatory, La Silla,Chile.Full Tables A.1 to A.4 are only available at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/535/A42
| Improved Astrometry and Photometry for the Luyten Catalog. II. Faint Stars and the Revised Catalog
We complete construction of a catalog containing improved astrometry andnew optical/infrared photometry for the vast majority of NLTT starslying in the overlap of regions covered by POSS I and by the secondincremental Two Micron All Sky Survey (2MASS) release, approximately 44%of the sky. The epoch 2000 positions are typically accurate to 130 mas,the proper motions to 5.5 mas yr-1, and the V-J colors to0.25 mag. Relative proper motions of binary components are measured to 3mas yr-1. The false-identification rate is ~1% for11<~V<~18 and substantially less at brighter magnitudes. Theseimprovements permit the construction of a reduced proper-motion diagramthat, for the first time, allows one to classify NLTT stars intomain-sequence (MS) stars, subdwarfs (SDs), and white dwarfs (WDs). We inturn use this diagram to analyze the properties of both our catalog andthe NLTT catalog on which it is based. In sharp contrast to popularbelief, we find that NLTT incompleteness in the plane is almostcompletely concentrated in MS stars, and that SDs and WDs are detectedalmost uniformly over the sky δ>-33deg. Our catalogwill therefore provide a powerful tool to probe these populationsstatistically, as well as to reliably identify individual SDs and WDs.
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Pozíciós és asztrometriai adatok
| Csillagkép: | Sas |
| Rektaszcenzió: | 22h28m19.62s |
| Deklináció: | -04°50'06.7" |
| Vizuális fényesség: | 10.342 |
| RA sajátmozgás: | 148.7 |
| Dec sajátmozgás: | -159.2 |
| B-T magnitude: | 11.643 |
| V-T magnitude: | 10.45 |
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