New extended atomic data in cool star model atmospheres

Grupp, F.; Kurucz, Robert L.; Tan, Kefeng

doi:10.1051/0004-6361/200912302

Cited by 44 publications

(44 citation statements)

References 22 publications

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“…All calculations are performed with plane-parallel, homogeneous, LTE, and blanketed model atmospheres computed with the MAFAGS-OS code (Grupp et al (2009)). …”

Section: Resultsmentioning

confidence: 99%

Fe I/Fe II ionization equilibrium in cool stars: NLTE versus LTE

Mashonkina¹,

Gehren²,

Shi³

et al. 2009

Proc. IAU

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Abstract. Non-local thermodynamic equilibrium (NLTE) line formation for neutral and singlyionized iron is considered through a range of stellar parameters characteristic of cool stars. A comprehensive model atom for Fe I and Fe II is presented. Our NLTE calculations support the earlier conclusions that the statistical equilibrium (SE) of Fe I shows an underpopulation of Fe I terms. However, the inclusion of the predicted high-excitation levels of Fe I in our model atom leads to a substantial decrease in the departures from LTE. As a test and first application of the Fe I/II model atom, iron abundances are determined for the Sun and four selected stars with well determined stellar parameters and high-quality observed spectra. Within the error bars, lines of Fe I and Fe II give consistent abundances for the Sun and two metal-poor stars when inelastic collisions with hydrogen atoms are taken into account in the SE calculations. For the close-to-solar metallicity stars Procyon and β Vir, the difference (Fe II -Fe I) is about 0.1 dex independent of the line formation model, either NLTE or LTE. We evaluate the influence of departures from LTE on Fe abundance and surface gravity determination for cool stars.

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“…All calculations are performed with plane-parallel, homogeneous, LTE, and blanketed model atmospheres computed with the MAFAGS-OS code (Grupp et al (2009)). …”

Section: Resultsmentioning

confidence: 99%

Fe I/Fe II ionization equilibrium in cool stars: NLTE versus LTE

Mashonkina¹,

Gehren²,

Shi³

et al. 2009

Proc. IAU

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“…In the same figure, the upper energy levels predicted by Kurucz (2009) in his calculations of the Fe i atomic structure are plotted by short bars. As described by Grupp et al (2009), the new calculations for iron included additional laboratory levels and more configurations than the earlier work of Kurucz (1992). It can be seen from Fig.…”

Section: Model Atommentioning

confidence: 96%

“…All calculations were performed with model atmospheres computed with the MAFAGS-OS code (Grupp 2004;Grupp et al 2009), which is based on up-to-date continuous opacities and includes the effects of line-blanketing by means of opacity sampling.…”

Section: Programs and Model Atmospheresmentioning

confidence: 99%

A non-LTE study of neutral and singly-ionized iron line spectra in 1D models of the Sun and selected late-type stars

Mashonkina

Gehren

Shi

et al. 2011

A&A

Self Cite

228

266

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Aims. We evaluate non-local thermodynamical equilibrium (non-LTE) line formation for the two ions of iron and check the ionization equilibrium between Fe i and Fe ii in model atmospheres of the cool reference stars based on the best available complete model atom for neutral and singly-ionized iron.Methods. We present a comprehensive model atom for Fe with more than 3000 measured and predicted energy levels. As a test and first application of the improved model atom, iron abundances are determined for the Sun and five stars with well determined stellar parameters and high-quality observed spectra. The efficiency of inelastic collisions with hydrogen atoms in the statistical equilibrium of iron is empirically estimated from inspection of their different influence on the Fe i and Fe ii lines in the selected stars. Results. Non-LTE leads to systematically depleted total absorption in the Fe i lines and to positive abundance corrections in agreement with the previous studies, however, the magnitude of such corrections is smaller compared to the earlier results. These non-LTE corrections do not exceed 0.1 dex for the solar metallicity and mildly metal-deficient stars, and they vary within 0.21 dex and 0.35 dex in the very metal-poor stars HD 84937 and HD 122563, respectively, depending on the assumed efficiency of collisions with hydrogen atoms. Based on the analysis of the Fe i/Fe ii ionization equilibrium in these two stars, we recommend to apply the Drawin formalism in non-LTE studies of Fe with a scaling factor of 0.1. For the Fe ii lines non-LTE corrections do not exceed 0.01 dex in absolute value over the whole range of stellar parameters that are considered. This study reveals two problems. The first one is that g f -values available for the Fe i and Fe ii lines are not accurate enough to pursue high-accuracy absolute stellar abundance determinations. For the Sun, the mean non-LTE abundance obtained from 54 Fe i lines is 7.56 ± 0.09 and the mean abundance from 18 Fe ii lines varies between 7.41 ± 0.11 and 7.56 ± 0.05 depending on the source of the g f -values. The second problem is that lines of Fe i give, on average, a 0.1 dex lower abundance compared with those of Fe ii lines for HD 61421 and HD 102870, even when applying a differential line-by-line analysis with regard to the Sun. A disparity between neutral atoms and first ions points to problems of stellar atmosphere modelling or/and effective temperature determination.

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“…In our copper abundance analysis, we applied the MAFAGS opacity sampling (OS) model atmosphere developed and updated by Grupp (2004) and Grupp et al (2009). This is a onedimensional plane-parallel model that is in hydrostatic equilibrium with chemical homogeneity throughout all the atmospheric layers.…”

Section: Copper Abundance Analysismentioning

confidence: 99%

Non-LTE analysis of copper abundances for the two distinct halo populations in the solar neighborhood

Yan

Shi

Nissen

et al. 2015

A&A

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Context. Two distinct halo populations were found in the solar neighborhood by a series of works. They can be clearly separated by [α/Fe] and several other elemental abundance ratios including [Cu/Fe]. Very recently, a non-local thermodynamic equilibrium (non-LTE) study revealed that relatively large departures exist between LTE and non-LTE results in copper abundance analysis. The study also showed that non-LTE effects of neutral copper vary with stellar parameters and thus affect the [Cu/Fe] trend. Aims. We aim to derive the copper abundances for the stars from the sample of Nissen & Schuster (2010) with both LTE and non-LTE calculations. Based on our results, we study the non-LTE effects of copper and investigate whether the high-α population can still be distinguished from the low-α population in the non-LTE [Cu/Fe] results. Methods. Our differential abundance ratios are derived from the high-resolution spectra collected from VLT/UVES and NOT/FIES spectrographs. Applying the MAFAGS opacity sampling atmospheric models and spectrum synthesis method, we derive the non-LTE copper abundances based on the new atomic model with current atomic data obtained from both laboratory and theoretical calculations. Conclusions. The non-LTE effects are strong for copper, especially in metal-poor stars. Our results confirmed that there are two distinct halo populations in the solar neighborhood. The dichotomy in copper abundance is a peculiar feature of each population, suggesting that they formed in different environments and evolved obeying diverse scenarios.

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New extended atomic data in cool star model atmospheres

Cited by 44 publications

References 22 publications

Fe I/Fe II ionization equilibrium in cool stars: NLTE versus LTE

Fe I/Fe II ionization equilibrium in cool stars: NLTE versus LTE

A non-LTE study of neutral and singly-ionized iron line spectra in 1D models of the Sun and selected late-type stars

Non-LTE analysis of copper abundances for the two distinct halo populations in the solar neighborhood

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