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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
| Detailed Analysis of Nearby Bulgelike Dwarf Stars. III. α-Element and Heavy-Element Abundances
The present sample of nearby bulgelike dwarf stars has kinematics andmetallicities characteristic of a probable inner disk or bulge origin.Ages derived by using isochrones give 10-11 Gyr for these stars, andmetallicities are in the range -0.80<=[Fe/H]<=+0.40. We calculatestellar parameters from spectroscopic data, and chemical abundances ofMg, Si, Ca, Ti, La, Ba, Y, Zr, and Eu are derived by using spectrumsynthesis. We found that [α-elements/Fe] show different patterns,depending on the element. Si/Fe, Ca/Fe, and Ti/Fe ratios declinesmoothly for increasing metallicities and essentially follow the diskpattern. O and Mg, products of massive supernovae, and also ther-process element Eu are overabundant relative to disk stars, showing asteeper decline for metallicities [Fe/H]>-0.3 dex, and[s-elements/Fe] roughly track the solar values, with no apparent trendwith metallicity for [Fe/H]<0, showing subsolar values for the metalrich stars. Both kinematical and chemical properties of the bulgelikestars indicate a distinct identity of this population when compared withdisk stars.
| 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.
| Detailed Analysis of Nearby Bulgelike Dwarf Stars. II. Lithium Abundances
Li abundances are derived for a sample of bulgelike stars withisochronal ages of 10-11 Gyr. These stars have orbits with pericentricdistances, Rp, as small as 2-3 kpc and Zmax<1kpc. The sample comprises G and K dwarf stars in the metallicity range-0.80<=[Fe/H]<=+0.40. Few data on Li abundances in old turnoffstars (>=4.5 Gyr) within the present metallicity range are available.M67 (4.7 Gyr) and NGC 188 (6 Gyr) are the oldest studied metal-rich openclusters with late-type stars. Li abundances have also been studied fora few samples of old metal-rich field stars. In the present work, a highdispersion in Li abundances is found for bulgelike stars with allmetallicity ranges, comparable with values in M67. The role ofmetallicity and age on a Li depletion pattern is discussed. The possibleconnection between Li depletion and oxygen abundance due to atmosphericopacity effects is investigated.
| Detailed Analysis of Nearby Bulgelike Dwarf Stars. I. Stellar Parameters, Kinematics, and Oxygen Abundances
High-resolution échelle spectra were obtained with the Fiber-fedExtended Range Optical Spectrograph at the 1.5 m ESO telescope for 35nearby bulgelike stars with metallicities in the range-0.8<=[Fe/H]<=+0.4. Geneva photometry, astrometric data fromHipparcos, and radial velocities from CORAVEL are available for thesestars. From Hipparcos data, it appears that the turnoff of thispopulation indicates an age of 10-11 Gyr (as stated by Grenon in 1999).Detailed analysis of the sample stars is carried out, and atmosphericparameters derived from spectroscopic and photometric determinations arepresented. Oxygen abundances are derived based on the forbidden [O I]6300.3 Å line. The results show an oxygen overabundance patternfor most of the sample stars when compared to their disk counterparts.Based on observations carried out at the European Southern Observatory,La Silla.
| Oxygen Abundances in Bulge-like Dwarf Stars
High resolution échelle spectra were obtained with the FEROSspectrograph at the 1.5m ESO telescope for 35 nearby bulge-like stars.From Hipparcos data it appears that the turn-off of this populationindicates an age of 10--11 Gyr (Grenon 2000). Oxygen abundances arecalculated using the [O I] line at 6300.3 Å. The derived resultsshow an oxygen overabundance for most of our sample stars when comparedto their disk counterparts.
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| קבוצת-כוכבים: | גדי |
| התרוממות ימנית: | 20h36m53.32s |
| סירוב: | -16°45'54.9" |
| גודל גלוי: | 10.288 |
| תנועה נכונה: | 11.6 |
| תנועה נכונה: | -181.2 |
| B-T magnitude: | 11.689 |
| V-T magnitude: | 10.404 |
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