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Titolo: Non-LTE line formation for NI/II: Abundances and stellar parameters - Model atom and first results on BA-type stars
Autore: Przybilla, N; Butler, K;
- Indirizzi:
- Univ Sternwarte Munchen, D-81679 Munich, Germany Univ Sternwarte Munchen Munich Germany D-81679 , D-81679 Munich, Germany
- Titolo Testata:
- ASTRONOMY & ASTROPHYSICS
fascicolo: 3,
volume: 379,
anno: 2001,
pagine: 955 - 975
- SICI:
- 1432-0746(200112)379:3<955:NLFFNA>2.0.ZU;2-Q
- Fonte:
- ISI
- Lingua:
- ENG
- Soggetto:
- CHEMICALLY PECULIAR STARS; SINGLY IONIZED NITROGEN; UPPER MAIN-SEQUENCE; A-TYPE SUPERGIANTS; LUMINOUS OB STARS; EFFECTIVE TEMPERATURES; OXYGEN ABUNDANCES; CROSS-SECTIONS; STATISTICAL EQUILIBRIUM; ATMOSPHERIC PARAMETERS;
- Keywords:
- atomic data; line : formation; stars : abundances, early-type, fundamental parameters, supergiants;
- Tipo documento:
- Article
- Natura:
- Periodico
- Settore Disciplinare:
- Physical, Chemical & Earth Sciences
- Citazioni:
- 88
- Recensione:
- Indirizzi per estratti:
- Indirizzo: Przybilla, N Univ Sternwarte Munchen, Scheinerstr 1, D-81679 Munich, Germany Univ Sternwarte Munchen Scheinerstr 1 Munich Germany D-81679
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- Citazione:
- N. Przybilla e K. Butler, "Non-LTE line formation for NI/II: Abundances and stellar parameters - Model atom and first results on BA-type stars", ASTRON ASTR, 379(3), 2001, pp. 955-975
Abstract
`A comprehensive model atom for non-LTE line formation calculations for neutral and singly-ionized nitrogen is presented. Highly accurate radiative and collisional atomic data are incorporated, recently determined for astrophysical and fusion research using the R-matrix method in the close-couplingapproximation. As a test and first application of the model, nitrogen abundances are determined on the basis of line-blanketed LTE model atmospheres for five stars, the main sequence object Vega (A0V) and the supergiants etaLeo (A0Ib), HD111613 (A2Iabe), HD92207 (A0Iae) and beta Ori (B8Iae), usinghigh S/N and high-resolution spectra at visual and near-IR wavelengths. The computed non-LTE line profiles fit the observations excellently for a given nitrogen abundance in each object. Moreover, the ionization equilibrium of NI/II proves to be a sensitive temperature indicator for late B-type andearly A-type supergiants - even at low metallicities - due to the apparentnitrogen overabundance in these objects. All supergiants within our sampleshow an enrichment of nitrogen on the order of similar to0.3-0.6 dex, indicating the mixing of CN-cycled material into atmospheric layers, with the sum of the CNO abundances staying close to solar. This finding is in accordance with recent stellar evolution models accounting for mass-loss and rotation. For Vega, an underabundance of nitrogen by 0.25 dex is found, in good agreement with the similar underabundance of other light elements. The dependence of the non-LTE effects on the atmospheric parameters is discussed with special emphasis on the supergiants where a strong radiation field at low particle densities favours deviations from LTE. Non-LTE effects systematically strengthen the NI/II lines. For some Ni lines in supergiants non-LTE abundance corrections in excess of 1 dex are found and they react sensitively to modifications of the collisional excitation data. The influence of microturbulence on the statistical-equilibrium calculations is also investigated: the line-strengths of the strong Ni features show some sensitivity dueto modifications of the line-formation depths and the departure coefficients, while the - in this parameter range - weak NII lines remain unaffected.
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Documento generato il 22/05/13 alle ore 06:07:37