A grid of non-local thermodynamic equilibrium corrections for magnesium and calcium in late-type giant and supergiant stars: application to Gaia

Merle, Thibault; Thévenin, F.; Pichon, B.; Bigot, Lionel

doi:10.1111/j.1365-2966.2011.19540.x

Cited by 50 publications

(53 citation statements)

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“…Several works in the literature have already tried to quantify the non-LTE effects in Mg and Si, and their dependence on the stellar parameters (e.g. Zhao & Gehren 2000;Shi et al 2011;Merle et al 2011;Sukhorukov & Shchukina 2012;Bergemann et al 2013). These works show that the non-LTE effects are usually stronger, being non-negligible for evolved, hot, and metal-poor stars.…”

Section: Resultsmentioning

confidence: 99%

From stellar to planetary composition: Galactic chemical evolution of Mg/Si mineralogical ratio

Adibekyan

Santos

Figueira

et al. 2015

A&A

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Aims. The main goal of this work is to study element ratios that are important for the formation of planets of different masses. Methods. We study potential correlations between the existence of planetary companions and the relative elemental abundances of their host stars. We use a large sample of FGK-type dwarf stars for which precise Mg, Si, and Fe abundances have been derived using HARPS high-resolution and high-quality data. Results. A first analysis of the data suggests that low-mass planet host stars show higher [Mg/Si] ratios, while giant planet hosts present [Mg/Si] that is lower than field stars. However, we found that the [Mg/Si] ratio significantly depends on metallicity through Galactic chemical evolution. After removing the Galactic evolution trend only the difference in the [Mg/Si] elemental ratio between low-mass planet hosts and non-hosts was present in a significant way. These results suggest that low-mass planets are more prevalent around stars with high [Mg/Si].Conclusions. Our results demonstrate the importance of Galactic chemical evolution and indicate that it may play an important role in the planetary internal structure and composition. The results also show that abundance ratios may be a very relevant issue for our understanding of planet formation and evolution.

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Section: Resultsmentioning

confidence: 99%

From stellar to planetary composition: Galactic chemical evolution of Mg/Si mineralogical ratio

Adibekyan

Santos

Figueira

et al. 2015

A&A

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“…The non-LTE correction for the Mg I abundances of both halo and Carina stars were not taken into account. However, Merle et al (2011) found that the non-LTE corrections to the EWs of two Mg lines at 5711 and 5528 Å are smaller than 10%.…”

Section: Comparison With the Galactic Halomentioning

confidence: 99%

“…We excluded the non-LTE corrections to the EWs of Ca I lines for both halo and Carina stars from the comparison. Merle et al (2011) found that the non-LTE corrections to the EWs of the two adopted Ca I lines (6122, 6166 Å) are smaller than 10%. The anonymous referee noted the paucity of subsolar [Mg/Fe] and [Ca/Fe] abundance ratios, plotted in panels (c) and (e) of Fig.…”

Section: Comparison With the Galactic Halomentioning

confidence: 99%

The Carina Project

Fabrizio

Nonino

Bono

et al. 2015

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We have performed a new abundance analysis of Carina red giant (RG) stars from spectroscopic data collected with UVES (high spectral resolution) and FLAMES/GIRAFFE (high and medium resolution) at ESO/VLT. The former sample includes 44 RGs, while the latter consists of 65 (high-resolution) and ∼800 (medium-resolution) RGs, covering a significant fraction of the galaxy's RG branch, and red clump stars. To improve the abundance analysis at the faint magnitude limit, the FLAMES/GIRAFFE data were divided into ten surface gravity and effective temperature bins. The spectra of the stars belonging to the same gravity and temperature bin were stacked. This approach allowed us to increase the signal-to-noise ratio in the faint magnitude limit (V ≥ 20.5 mag) by at least a factor of five. We took advantage of the new photometry index c U,B,I introduced recently as an age and probably a metallicity indicator to split stars along the red giant branch. These two stellar populations display distinct [Fe/H] and [Mg/H] distributions: their mean iron abundances are −2.15 ± 0.06 dex (σ = 0.28), and −1.75 ± 0.03 dex (σ = 0.21), respectively. The two iron distributions differ at the 75% level. This supports preliminary results. Moreover, we found that the old and intermediate-age stellar populations have mean [Mg/H] abundances of −1.91 ± 0.05 dex (σ = 0.22) and −1.35 ± 0.03 dex (σ = 0.22); these differ at the 83% level. Carina's α-element abundances agree, within 1σ, with similar abundances for field halo stars and for cluster (Galactic and Magellanic) stars. The same outcome applies to nearby dwarf spheroidals and ultra-faint dwarf galaxies in the iron range covered by Carina stars. Finally, we found evidence of a clear correlation between Na and O abundances, thus suggesting that Carina's chemical enrichment history is quite different from that in the globular clusters.

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“…No hydrogen collisions were included by them since, as they mentioned, hydrogen collisions will be unimportant in A-stars, the subject of that study. Merle et al (2011) used an updated model atom to study the non-LTE effects on lines to be observed by the Gaia satellite. The model atom included levels with nl quantum numbers up to n = 10 and l = 9, including fine structure at low l, leading to a 149 level model atom.…”

Section: Previous Workmentioning

confidence: 99%

Mg line formation in late-type stellar atmospheres

Osorio

Barklem

Lind

et al. 2015

A&A

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Context. Magnesium is an element of significant astrophysical importance, often traced in late-type stars using lines of neutral magnesium, which is expected to be subject to departures from local thermodynamic equilibrium (LTE). The importance of Mg, together with the unique range of spectral features in late-type stars probing different parts of the atom, as well as its relative simplicity from an atomic physics point of view, makes it a prime target and test bed for detailed ab initio non-LTE modelling in stellar atmospheres. Previous non-LTE modelling of spectral line formation has, however, been subject to uncertainties due to lack of accurate data for inelastic collisions with electrons and hydrogen atoms. Aims. In this paper we build and test a Mg model atom for spectral line formation in late-type stars with new or recent inelastic collision data and no associated free parameters. We aim to reduce these uncertainties and thereby improve the accuracy of Mg non-LTE modelling in late-type stars.Methods. For the low-lying states of Mg i, electron collision data were calculated using the R-matrix method. Hydrogen collision data, including charge transfer processes, were taken from recent calculations by some of us. Calculations for collisional broadening by neutral hydrogen were also performed where data were missing. These calculations, together with data from the literature, were used to build a model atom. This model was then employed in the context of standard non-LTE modelling in 1D (including average 3D) model atmospheres in a small set of stellar atmosphere models. First, the modelling was tested by comparisons with observed spectra of benchmark stars with well-known parameters. Second, the spectral line behaviour and uncertainties were explored by extensive experiments in which sets of collisional data were changed or removed. Results. The modelled spectra agree well with observed spectra from benchmark stars, showing much better agreement with line profile shapes than with LTE modelling. The line-to-line scatter in the derived abundances shows some improvements compared to LTE (where the cores of strong lines must often be ignored), particularly when coupled with averaged 3D models. The observed Mg emission features at 7 and 12 μm in the spectra of the Sun and Arcturus, which are sensitive to the collision data, are reasonably well reproduced. Charge transfer with H is generally important as a thermalising mechanism in dwarfs, but less so in giants. Excitation due to collisions with H is found to be quite important in both giants and dwarfs. The R-matrix calculations for electron collisions also lead to significant differences compared to when approximate formulas are employed. The modelling predicts non-LTE abundance corrections ΔA(Mg) NLTE−LTE in dwarfs, both solar metallicity and metal-poor, to be very small (of order 0.01 dex), even smaller than found in previous studies. In giants, corrections vary greatly between lines, but can be as large as 0.4 dex. Conclusions. Our results emphasise ...

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A grid of non-local thermodynamic equilibrium corrections for magnesium and calcium in late-type giant and supergiant stars: application to Gaia

Cited by 50 publications

References 70 publications

From stellar to planetary composition: Galactic chemical evolution of Mg/Si mineralogical ratio

From stellar to planetary composition: Galactic chemical evolution of Mg/Si mineralogical ratio

The Carina Project

Mg line formation in late-type stellar atmospheres

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