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Oxygen line formation in late-F through early-K disk/halo stars. Infrared O I triplet and [O I] lines
In order to investigate the formation of O I 7771-5 and [O I] 6300/6363lines, extensive non-LTE calculations for neutral atomic oxygen werecarried out for wide ranges of model atmosphere parameters, which areapplicable to early-K through late-F halo/disk stars of variousevolutionary stages.The formation of the triplet O I lines was found to be well described bythe classical two-level-atom scattering model, and the non-LTEcorrection is practically determined by the parameters of theline-transition itself without any significant relevance to the detailsof the oxygen atomic model. This simplifies the problem in the sensethat the non-LTE abundance correction is essentially determined only bythe line-strength (Wlambda ), if the atmospheric parametersof Teff, log g, and xi are given, without any explicitdependence of the metallicity; thus allowing a useful analytical formulawith tabulated numerical coefficients. On the other hand, ourcalculations lead to the robust conclusion that LTE is totally valid forthe forbidden [O I] lines.An extensive reanalysis of published equivalent-width data of O I 7771-5and [O I] 6300/6363 taken from various literature resulted in theconclusion that, while a reasonable consistency of O I and [O I]abundances was observed for disk stars (-1 <~ [Fe/H] <~ 0), theexistence of a systematic abundance discrepancy was confirmed between OI and [O I] lines in conspicuously metal-poor halo stars (-3 <~[Fe/H] <~ -1) without being removed by our non-LTE corrections, i.e.,the former being larger by ~ 0.3 dex at -3 <~ [Fe/H] <~ -2.An inspection of the parameter-dependence of this discordance indicatesthat the extent of the discrepancy tends to be comparatively lessenedfor higher Teff/log g stars, suggesting the preference ofdwarf (or subgiant) stars for studying the oxygen abundances ofmetal-poor stars.Tables 2, 5, and 7 are 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/402/343 and Table\ref{tab3} is only available in electronic form athttp://www.edpsciences.org
| The dwarf star content of elliptical and lenticular galaxies
Near-IR spectra of 14 galaxies are analyzed to determine accurate lowermain-sequence dwarf light contributions and to set limits on themass-to-light (M/L) ratios. While dwarf light contributes 30-50 percentof the total at 8200 A, low measured FeH indices preclude contributionsof more than 15 percent to the integrated light at 9900 A from late Mdwarfs. M/L ratios of about 6 are found, consistent with dynamicalestimates. The brighter galaxies exhibit substantial gradients in theequivalent width of the Na I feature. This is at least partly due tometal abundance gradients also reflected in the TiO index, but there issome evidence for concentrations of metal-rich dwarfs toward the centersof giant galaxies.
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Pozíciós és asztrometriai adatok
| Csillagkép: | Halak |
| Rektaszcenzió: | 00h25m45.69s |
| Deklináció: | +18°26'09.5" |
| Vizuális fényesség: | 9.038 |
| RA sajátmozgás: | -46.7 |
| Dec sajátmozgás: | -73 |
| B-T magnitude: | 9.701 |
| V-T magnitude: | 9.093 |
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