Chemical abundances in metal-poor giants: limitations imposed by the use of classical 1D stellar atmosphere models

Dobrovolskas, V.; Kučinskas, A.; Ludwig, H. G.; Caffau, E.; Klevas, J.; Prakapavičius, D.

doi:10.22323/1.100.0288

Cited by 7 publications

(11 citation statements)

References 6 publications

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“…Remarkably, at [M/H] = −3.0 this may result in differences A&A 549, A14 (2013) of up to −1.0 dex in the abundances of chemical elements derived with the 3D hydrodynamical and classical 1D model atmospheres. This result was later confirmed by Dobrovolskas et al (2010) and Ivanauskas et al (2010), who used different 3D hydrodynamical stellar atmosphere and spectrum synthesis codes, CO 5 BOLD and Linfor3D, respectively, together with the atmospheric parameters of red giants similar to those utilized by Collet et al (2007). All these studies unequivocally point to the fact that the role of convection in the atmospheres of red giant stars may be significantly more important than previously thought, especially at metallicities [M/H] < ∼ −1.0.…”

Section: Introductionmentioning

confidence: 54%

“…This approach allowed us to cover a range in λ c and χ to quantify the trends of line formation properties in the 3D hydrodynamical and 1D classical model atmospheres with respect to these two line parameters. Conceptually, this method can be traced back to the work of Steffen & Holweger (2002) and was applied in several later studies too (e.g., Collet et al 2007;Dobrovolskas et al 2010;Ivanauskas et al 2010). Synthetic line profiles were calculated for the following tracer species of astrophysical interest: Fictitious lines were calculated at three wavelengths, λ c = 400, 850, and 1600 nm.…”

Section: One-dimensional (1d) Modelmentioning

confidence: 99%

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Three-dimensional hydrodynamical CO⁵BOLD model atmospheres of red giant stars

Kučinskas¹,

Steffen²,

Ludwig³

et al. 2012

A&A

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Aims. We investigate the role of convection in the formation of atomic and molecular lines in the atmosphere of a red giant star. For this purpose we study the formation properties of spectral lines that belong to a number of astrophysically important tracer elements, including neutral and singly ionized atoms (Li Ba ii, and Eu ii), and molecules (CH, CO, C 2 , NH, CN, and OH).Methods. We focus our investigation on a prototypical red giant located close to the red giant branch (RGB) tip (T eff = 3660 K, log g = 1.0, [M/H] = 0.0). We used two types of model atmospheres, 3D hydrodynamical and classical 1D, calculated with the CO 5 BOLD and LHD stellar atmosphere codes, respectively. Both codes share the same atmospheric parameters, chemical composition, equation of state, and opacities, which allowed us to make a strictly differential comparison between the line formation properties predicted in 3D and 1D. The influence of convection on the spectral line formation was assessed with the aid of 3D-1D abundance corrections, which measure the difference between the abundances of chemical species derived with the 3D hydrodynamical and 1D classical model atmospheres. Results. We find that convection plays a significant role in the spectral line formation in this particular red giant. The derived 3D-1D abundance corrections rarely exceed ±0.1 dex when lines of neutral atoms and molecules are considered, which is in line with the previous findings for solar-metallicity red giants located on the lower RGB. The situation is different with lines that belong to ionized atoms, or to neutral atoms with high ionization potential. In both cases, the corrections for high-excitation lines (χ > 8 eV) may amount to Δ 3D−1D ∼ −0.4 dex. The 3D-1D abundance corrections generally show a significant wavelength dependence; in most cases they are smaller in the near-infrared, at 1600-2500 nm.

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Section: Introductionmentioning

confidence: 54%

Section: One-dimensional (1d) Modelmentioning

confidence: 99%

Three-dimensional hydrodynamical CO⁵BOLD model atmospheres of red giant stars

Kučinskas¹,

Steffen²,

Ludwig³

et al. 2012

A&A

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“…Even considering that the atmospheric parameters are not exactly the same in both their and our models, the corrections of Collet and collaborators appear noticeably larger. This is also the case for other species (see Ivanauskas et al 2010;Dobrovolskas et al 2010) and the reason is not yet understood.…”

Section: Abundance Corrections For the Hf R9 And Forbidden O Linesmentioning

confidence: 94%

Fluorine Abundances of Galactic Low-Metallicity Giants

Ludwig

Caffau

et al. 2013

ApJ

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With abundances and 2σ upper limits of fluorine (F) in seven metal-poor field giants, nucleosynthesis of stellar F at low metallicity is discussed. The measurements are derived from the HF(1-0) R9 line at 23358 Å using nearinfrared K-band high-resolution spectra obtained with CRIRES at the Very Large Telescope. The sample reaches lower metallicities than previous studies on F of field giants, ranging from [Fe/H] = −1.56 down to −2.13. Effects of three-dimensional model atmospheres on the derived F and O abundances are quantitatively estimated and shown to be insignificant for the program stars. The observed F yield in the form of [F/O] is compared with two sets of Galactic chemical evolution models, which quantitatively demonstrate the contribution of Type II supernova (SN II) ν-process and asymptotic giant branch/Wolf-Rayet stars. It is found that at this low-metallicity region, models cannot well predict the observed distribution of [F/O], while the observations are better fit by models considering an SN II ν-process with a neutrino energy of E ν = 3 × 10 53 erg. Our sample contains HD 110281, a retrograde orbiting low-α halo star, showing a similar F evolution as globular clusters. This supports the theory that such halo stars are possibly accreted from dwarf galaxy progenitors of globular clusters in the halo.

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“…However, the positive sign of the 3D-1D abundance differences indicates that in the spectra of red giants in NGC 6752 the three studied Ba II lines will be weaker in 3D than in 1D, in contrast to what is generally seen in red giants at this metallicity (cf. Collet et al 2007;Dobrovolskas et al 2010). …”

Section: The 3d-corrected 1d Nlte Barium Abundance In Ngc 6752mentioning

confidence: 99%

“…A step beyond these limitations can be made by using threedimensional (3D) hydrodynamical atmosphere models that account for the three-dimensionality and non-stationarity of stellar atmospheres from first principles. Recent work has shown that significant differences may be expected between stellar abundances derived using 3D hydrodynamical and classical 1D model atmospheres (Collet et al 2007(Collet et al , 2009González Hernández et al 2009;Ramírez et al 2009;Behara et al 2010;Dobrovolskas et al 2010;Ivanauskas et al 2010; see also Asplund 2005, for a review of earlier work). These differences become larger at lower metallicities and at their extremes may reach 1 dex (!…”

Section: Introductionmentioning

confidence: 99%

Barium abundance in red giants of NGC 6752

Dobrovolskas¹,

Kučinskas²,

Andrievsky³

et al. 2012

A&A

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Aims. We study the effects related to departures from non-local thermodynamic equilibrium (NLTE) and homogeneity in the atmospheres of red giant stars, to assess their influence on the formation of Ba II lines. We estimate the impact of these effects on the barium abundance determinations for 20 red giants in Galactic globular cluster NGC 6752. Methods. One-dimensional (1D) local thermodynamic equilibrium (LTE) and 1D NLTE barium abundances were derived using classical 1D ATLAS9 stellar model atmospheres. The three-dimensional (3D) LTE abundances were obtained for 8 red giants on the lower RGB, by adjusting their 1D LTE abundances using 3D-1D abundance corrections, i.e., the differences between the abundances obtained from the same spectral line using the 3D hydrodynamical and classical 1D stellar model atmospheres. The 3D-1D abundance corrections were obtained in a strictly differential way using the 3D hydrodynamical and classical 1D codes CO 5 BOLD and LHD. Both codes utilized identical stellar atmospheric parameters, opacities, and equation of state. Results. The mean 1D barium-to-iron abundance ratios derived for 20 giants are [Ba/Fe] 1D LTE = 0.24 ± 0.05(stat.) ± 0.08(sys.) and [Ba/Fe] 1D NLTE = 0.05 ± 0.06(stat.) ± 0.08(sys.). The 3D-1D abundance correction obtained for 8 giants is small (∼+0.05 dex), thus leads to only minor adjustment when applied to the mean 1D NLTE barium-to-iron abundance ratio for the 20 giants, [Ba/Fe] 3D+NLTE = 0.10 ± 0.06(stat.) ± 0.10(sys.). The intrinsic abundance spread between the individual cluster stars is small and can be explained in terms of uncertainties in the abundance determinations. Conclusions. Deviations from LTE play an important role in the formation of barium lines in the atmospheres of red giants studied here. The role of 3D hydrodynamical effects should not be dismissed either, even if the obtained 3D-1D abundance corrections are small. This result is a consequence of subtle fine-tuning of individual contributions from horizontal temperature fluctuations and differences between the average temperature profiles in the 3D and 1D model atmospheres: owing to the comparable size and opposite sign, their contributions nearly cancel each other. This fine-tuning is characteristic of the particular set of atmospheric parameters and the element investigated, hence should not necessarily be a general property of spectral line formation in the atmospheres of red giant stars.

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Chemical abundances in metal-poor giants: limitations imposed by the use of classical 1D stellar atmosphere models

Cited by 7 publications

References 6 publications

Three-dimensional hydrodynamical CO⁵BOLD model atmospheres of red giant stars

Three-dimensional hydrodynamical CO⁵BOLD model atmospheres of red giant stars

Fluorine Abundances of Galactic Low-Metallicity Giants

Barium abundance in red giants of NGC 6752

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Chemical abundances in metal-poor giants: limitations imposed by the use of classical 1D stellar atmosphere models

Cited by 7 publications

References 6 publications

Three-dimensional hydrodynamical CO5BOLD model atmospheres of red giant stars

Three-dimensional hydrodynamical CO5BOLD model atmospheres of red giant stars

Fluorine Abundances of Galactic Low-Metallicity Giants

Barium abundance in red giants of NGC 6752

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Product

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Three-dimensional hydrodynamical CO⁵BOLD model atmospheres of red giant stars

Three-dimensional hydrodynamical CO⁵BOLD model atmospheres of red giant stars