Spectroscopic analysis of nearby lower-main-sequence stars

Wang, X. M.; Shi, Jianrong; Zhao, Gang

doi:10.1111/j.1365-2966.2009.15241.x

Cited by 4 publications

(4 citation statements)

References 57 publications

(131 reference statements)

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“…However, some doubt still remains regarding whether this effect is really so important. Wang et al (2009) carried out spectroscopic analysis of 30 nearby lower main-sequence stars at 4700 T eff 5400 K. They could not confirm the appreciable T eff -dependent systematic discrepancy reported by Kotoneva et al (2006), but found a reasonable consistency between Fe i and Fe ii abundances to a level of 0.1 dex (cf. Fig.…”

Section: Introductionmentioning

confidence: 83%

“…It may be worth comparing the spectroscopic parameters with those determined by other methods in recent representative studies. The comparisons with the results of Wang et al (2009), Ramírez et al (2013), andLuck (2017) are shown in Figures 8, 9, and 10, respectively. In all three investigations, T eff was determined photometrically from colors, log g by comparing the position on the log L vs. log T eff diagram (L: stellar luminosity) with stellar evolutionary tracks, and v t by requiring that the resulting abundances from Fe i lines do not show any systematic correlation with line strengths (though v t = 1 km s −1 was assumed by Wang et al 2009).…”

Section: Reliability Of Spectroscopic Parametersmentioning

confidence: 93%

“…• Regarding v t , while Ramírez et al's (2013) results are almost consistent with our determination (Figure 9c), those of Luck (2017) show some systematic trend (Figure 10c) that they tend to be larger for higher v t (while somewhat smaller for lower v t ). We can see from Figure 8c that v t = 1 km s −1 assumed by Wang et al (2009) was not so a bad choice.…”

Section: Reliability Of Spectroscopic Parametersmentioning

confidence: 93%

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Spectroscopic Determination of Stellar Parameters and Oxygen Abundances for Hyades/Field G–K Dwarfs

Takeda

Honda

2020

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It has been occasionally suggested that Fe abundances of K dwarfs derived from Fe i and Fe ii lines show considerable discrepancies and oxygen abundances determined from high-excitation O i 7771-5 triplet lines are appreciably overestimated (the problem becoming more serious towards lower T eff ), which however has not yet been widely confirmed. With an aim to clarify this issue, we spectroscopically determined the atmospheric parameters of 148 G-K dwarfs (Hyades cluster stars and field stars) by assuming the classical Fe i/Fe ii ionization equilibrium as usual, and determined their oxygen abundances by applying the non-LTE spectrum fitting analysis to O i 7771-5 lines. It turned out that the resulting parameters did not show any significant inconsistency with those determined by other methods (for example, the mean differences in T eff and log g from the well-determined solutions of Hyades dwarfs are mostly 100 K and 0.1 dex). Likewise, the oxygen abundances of Hyades stars are around [O/H] ∼ +0.2 dex (consistent with the metallicity of this cluster) without exhibiting any systematic T eff -dependence. Accordingly, we conclude that parameters can be spectroscopically evaluated to a sufficient precision in the conventional manner (based on the Saha-Boltzmann equation for Fe i/Fe ii) and oxygen abundances can be reliably determined from the O i 7771-5 triplet for K dwarfs as far as stars of T eff 4500 K are concerned. We suspect that previously reported strongly T eff -dependent discrepancies may have stemmed mainly from overestimation of weak-line strengths and/or improper T eff scale.

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Section: Introductionmentioning

confidence: 83%

Section: Reliability Of Spectroscopic Parametersmentioning

confidence: 93%

Section: Reliability Of Spectroscopic Parametersmentioning

confidence: 93%

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Spectroscopic Determination of Stellar Parameters and Oxygen Abundances for Hyades/Field G–K Dwarfs

Takeda

Honda

2020

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“…Meanwhile, efforts of investigating the non-LTE effect on K i 7699 by non-LTE calculations with sufficiently complex atomic model of K have been made by several investigators not only for the Sun (de la Reza & Müller 1975;Bruls et al 1992;Zhang et al 2006a) but also for stars of other types (Takeda et al 1996;Ivanova & Shimanskiȋ 2000;Takeda et al 2002;Shimansky et al 2003;Zhang et al 2006b;Andrievsky et al 2010;Reggiani et al 2019). Making use of these theoretical accomplishments, chemical evolution studies of potassium based on the non-LTE abundances derived from K i 7699 have gradually emerged since the beginning of this century, where the targets of those investigations are roughly divided into two groups: (i) mildly metal-poor or metal-rich stars of disk population (−1 < ∼ [Fe/H] < ∼ 0.5) (Takeda et al 2002;Zhang et al 2006b;Wang et al 2009;Zhao et al 2016;Reggiani et al 2019) and (ii) very metal-poor stars of halo population(−4 < ∼ [Fe/H] < ∼ −2) (Cayrel et al 2004;Takeda et al 2009;Andrievsky et al 2010;Roederer et al 2014;Reggiani et al 2019).…”

Section: Introductionmentioning

confidence: 99%

Determination of Potassium Abundances for Giant and Dwarf Stars in the Galactic Disk

Takeda

2020

Preprint

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An extensive study on the potassium abundances of late-type stars was carried out by applying the non-LTE spectrum-fitting analysis to the K i resonance line at 7698.96 Å to a large sample of 160 FGK dwarfs and 328 late-G /early-K giants (including 89 giants in the Kepler field with seismologically known ages) belonging to the disk population (−1 < ∼ [Fe/H] < ∼ 0.5), which may provide important observational constraint on the nucleosynthesis history of K in the galactic disk. Special attention was paid to clarifying the observed behaviors of [K/Fe] in terms of [Fe/H] along with stellar age, and to checking whether giants and dwarfs yield consistent results with each other. The following results were obtained. (1) A slightly increasing tendency of [K/Fe] with a decrease in [Fe/H] (d[K/Fe]/d[Fe/H] ∼ −0.1 to −0.15; a shallower slope than reported by previous studies) was confirmed for FGK dwarfs, though thick-disk stars tend to show larger [K/Fe] deviating from this gradient. (2) Almost similar characteristics was observed also for apparently bright field giants locating in the solar neighborhood (such as like dwarfs). (3) However, the [K/Fe] vs. [Fe/H] relation for more distant Kepler giants shows larger scatter and is systematically higher (by < ∼ 0.1 dex) than that of dwarfs, implying that chemical evolution of K is rather diversified depending on the position in the Galaxy. ( 4) Regarding the age-dependence, a marginal trend of increasing [K/Fe] with age is recognized for dwarfs, while any systematic tendency is not observed for Kepler giants. These consequences may suggest that evolution of [K/Fe] with time in the galactic disk does exist but proceeded more gradually than previously thought, and its condition is appreciably location-dependent.

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Nlte Analysis of High-Resolution H-Band Spectra. I. Neutral Silicon*

Zhang

Shi

Pan

et al. 2016

ApJ

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We investigated the reliability of our silicon atomic model and the influence of non-local thermodynamical equilibrium (NLTE) on the formation of neutral silicon (Si I) lines in the near-infrared (near-IR) H-band. We derived the differential Si abundances for 13 sample stars with high-resolution H-band spectra from the Apache Point Observatory Galactic Evolution Experiment (APOGEE), as well as from optical spectra, both under local thermodynamical equilibrium (LTE) and NLTE conditions. We found that the differences between the Si abundances derived from the H-band and from optical lines for the same stars are less than 0.1 dex when the NLTE effects included, and that NLTE reduces the line-to-line scatter in the H-band spectra for most sample stars. These results suggest that our Si atomic model is appropriate for studying the formation of H-band Si lines. Our calculations show that the NLTE corrections of the Si I H-band lines are negative, i.e. the final Si abundances will be overestimated in LTE. The corrections for strong lines depend on surface gravity, and tend to be larger for giants, reaching ∼ −0.2 dex in our sample, and up to ∼ −0.4 dex in extreme cases of APOGEE targets. Thus, the NLTE effects should be included in deriving silicon abundances from H-band Si I lines, especially for the cases where only strong lines are available.

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Spectroscopic analysis of nearby lower-main-sequence stars

Cited by 4 publications

References 57 publications

Spectroscopic Determination of Stellar Parameters and Oxygen Abundances for Hyades/Field G–K Dwarfs

Spectroscopic Determination of Stellar Parameters and Oxygen Abundances for Hyades/Field G–K Dwarfs

Determination of Potassium Abundances for Giant and Dwarf Stars in the Galactic Disk

Nlte Analysis of High-Resolution H-Band Spectra. I. Neutral Silicon*

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