Potassium abundances in nearby metal-poor stars

Zhang, H. W.; Gehren, T.; Butler, K.; Shi, Jianrong; Zhao, Gang

doi:10.1051/0004-6361:20064909

Cited by 42 publications

(47 citation statements)

References 30 publications

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“…Similar conclusion was drawn by Shimansky et al (2003) and Zhang et al (2006b) based on non-LTE determinations of the potassium abundance in the mildly metal-poor ([Fe/H] > −1) stars.…”

Section: Galactic Abundance Trends: Non-lte Vs Ltesupporting

confidence: 84%

Non-LTE line formation for heavy elements in four very metal-poor stars

Mashonkina¹,

Zhao

Gehren³

et al. 2007

A&A

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111

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Aims. Stellar parameters and abundances of Na, Mg, Al, K, Ca, Sr, Ba, and Eu are determined for four very metal-poor (VMP) stars (−2.15 ≥ [Fe/H] ≥ −2.66). For two of them, HD 84937 and HD 122563, the fraction of the odd isotopes of Ba derived for the first time.Methods. Determination of an effective temperature, surface gravity, and element abundances was based on non-local thermodynamic equilibrium (non-LTE) line formation and analysis of high-resolution (R ∼ 60 000 and 90 000) high signal-to-noise (S/N ≥ 200) observed spectra. A model atom for H i is presented. An effective temperature was obtained from the Balmer H α and H β line wing fits. The surface gravity was calculated from the Hipparcos parallax if available and the non-LTE ionization balance between Ca i and Ca ii. Based on the hyperfine structure affecting the Ba ii resonance line λ 4554, the fractional abundance of the odd isotopes of Ba was derived from a requirement that Ba abundances from the resonance line and subordinate lines of Ba ii must be equal.Results. For each star, non-LTE leads to a consistency of T eff from two Balmer lines and to a higher temperature compared to the LTE case, by up to 60 K. Non-LTE effects are important in spectroscopic determination of surface gravity from the ionization balance between Ca i and Ca ii. For each star with a known trigonometric surface gravity, non-LTE abundances from the lines of two ionization stages, Ca i and Ca ii, agree within the error bars, while a difference in the LTE abundances consists of 0.23 dex to 0.40 dex for different stars. Departures from LTE are found to be significant for all investigated atoms, and they strongly depend on stellar parameters. For HD 84937, the Eu/Ba ratio is consistent with the relative solar system r-process abundances, and the fraction of the odd isotopes of Ba, f odd , equals 0.43 ± 0.14. The latter can serve as an observational constraint on r-process models. The lower Eu/Ba ratio and f odd = 0.22 ± 0.15 found for HD 122563 suggest that the s-process or the unknown process has contributed significantly to the Ba abundance in this star.

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“…Similar conclusion was drawn by Shimansky et al (2003) and Zhang et al (2006b) based on non-LTE determinations of the potassium abundance in the mildly metal-poor ([Fe/H] > −1) stars.…”

Section: Galactic Abundance Trends: Non-lte Vs Ltesupporting

confidence: 84%

Non-LTE line formation for heavy elements in four very metal-poor stars

Mashonkina¹,

Zhao

Gehren³

et al. 2007

A&A

Self Cite

111

122

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“…To take into account collisions of potassium atoms with hydrogen atoms we applied the formula of Steenbock & Holweger (1984) with a correcting factor equal to 0.05. A similar correcting factor was used by Zhang et al (2006).…”

Section: Potassiummentioning

confidence: 99%

“…The models of Kobayashi et al (2006) (supernovae and hypernovae with Z = 0.0) seem also able to represent the relative abundances of O, Na, Mg and Al, but here again the production of potassium is strongly underestimated. We have added in the figure the determinations of Gehren et al (2004Gehren et al ( , 2006, of Mashonkina et al (2008), andZhang et al (2006) in the Galactic disk and halo. All these determinations have been done including the NLTE effects on the line profiles.…”

Section: Abundances Of O and Light Metals Relative To Mg In The Earlymentioning

confidence: 99%

Non-LTE abundances of Mg and K in extremely metal-poor stars and the evolution of [O/Mg], [Na/Mg], [Al/Mg], and [K/Mg] in the Milky Way

Andrievsky¹,

Spite²,

Коротин³

et al. 2010

A&A

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126

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Aims. LTE abundances of light elements in extremely metal-poor (EMP) stars have been previously derived from high quality spectra. New derivations, free from the NLTE effects, will better constrain the models of the Galactic chemical evolution and the yields of the very first supernovae. Methods. The NLTE profiles of the magnesium and potassium lines have been computed in a sample of 53 extremely metal-poor stars with a modified version of the program MULTI and adjusted to the observed lines in order to derive the abundances of these elements. Results. The NLTE corrections for magnesium and potassium are in good agreement with the works found in the literature. The abundances are slightly changed, reaching a better precision: the scatter around the mean of the abundance ratios has decreased. Magnesium may be used with confidence as reference element. Together with previously determined NLTE abundances of sodium and aluminum, the new ratios are displayed, for comparison, along the theoretical trends proposed by some models of the chemical evolution of the Galaxy, using different models of supernovae.

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“…principles of non-LTE (NLTE) line formation and codes capable of such calculations have been around for a long time but have only been explored in a more systematic fashion for a wide range of stellar parameters over the past decade or so (e.g., Zhao et al 1998;Zhao & Gehren 2000;Mashonkina & Gehren 2001;Takeda et al 2002;Gehren et al 2004;Fabbian et al 2006;Mashonkina & Zhao 2006;Zhang et al 2006b;Mashonkina et al 2007aMashonkina et al , 2008Bergemann & Gehren 2008;Zhang et al 2008;Lind et al 2009;Shi et al 2009;Andrievsky et al 2010;Bergemann & Cescutti 2010;Spite et al 2011Spite et al , 2012Yan et al 2015). Before the observations are used to give constraints to the GCE models, we need to take into account the analysis errors of the stellar abundances, such as the departures from LTE and uncertainties in the atmospheric parameters.…”

Section: Introductionmentioning

confidence: 99%

SYSTEMATIC NON-LTE STUDY OF THE −2.6 ≤ [Fe/H] ≤ 0.2 F AND G DWARFS IN THE SOLAR NEIGHBORHOOD. II. ABUNDANCE PATTERNS FROM Li TO Eu*

Zhao

Mashonkina

Yan

et al. 2016

ApJ

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147

158

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For the first time, we present an extensive study of stars with individual non-LTE (NLTE) abundances for 17 chemical elements from Li to Eu in a sample of stars uniformly distributed over the −2.62 [Fe/H] +0.24 metallicity range that is suitable for the Galactic chemical evolution research. The star sample has been kinematically selected to trace the Galactic thin and thick disks and halo. We find new results and improve earlier ones as follows: (i) the element-to-iron ratios for Mg, Si, Ca, and Ti form a metal-poor (MP) plateau at a similar height of 0.3 dex, and the knee occurs at common

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Potassium abundances in nearby metal-poor stars

Cited by 42 publications

References 30 publications

Non-LTE line formation for heavy elements in four very metal-poor stars

Non-LTE line formation for heavy elements in four very metal-poor stars

Non-LTE abundances of Mg and K in extremely metal-poor stars and the evolution of [O/Mg], [Na/Mg], [Al/Mg], and [K/Mg] in the Milky Way

SYSTEMATIC NON-LTE STUDY OF THE −2.6 ≤ [Fe/H] ≤ 0.2 F AND G DWARFS IN THE SOLAR NEIGHBORHOOD. II. ABUNDANCE PATTERNS FROM Li TO Eu*

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