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Accurate abundance patterns of solar twins and analogs. Does the anomalous solar chemical composition come from planet formation?
We derive the abundance of 19 elements in a sample of 64 stars withfundamental parameters very similar to solar, which minimizes the impactof systematic errors in our spectroscopic 1D-LTE differential analysis,using high-resolution (R?60 000), high signal-to-noise ratio(S/N?200) spectra. The estimated errors in the elemental abundancesrelative to solar are as small as ?0.025 dex. The abundance ratios[X/Fe] as a function of [Fe/H] agree closely with previously establishedpatterns of Galactic thin-disk chemical evolution. Interestingly, themajority of our stars show a significant correlation between [X/Fe] andcondensation temperature (T_C). In the sample of 22 stars withparameters closest to solar, we find that, on average, low TCelements are depleted with respect to high TC elements in thesolar twins relative to the Sun by about 0.08 dex (?20%). Anincreasing trend is observed for the abundances as a function ofTC for 900
| 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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Gözlemler ve gökölçümü verileri
| Takýmyýldýz: | Oglak |
| Sað Açýklýk: | 21h10m07.93s |
| Yükselim: | -24°49'23.2" |
| Görünürdeki Parlaklýk: | 8.541 |
| Uzaklýk: | 52.994 parsek |
| özdevim Sað Açýklýk: | 174.9 |
| özdevim Yükselim: | -36.6 |
| B-T magnitude: | 9.344 |
| V-T magnitude: | 8.608 |
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