Mg line formation in late-type stellar atmospheres

Osorio, Yeisson; Barklem, P. S.

doi:10.1051/0004-6361/201526958

Cited by 56 publications

(53 citation statements)

References 32 publications

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“…Here, we focus on the NLTE abundance corrections in our program stars, and explore the sensitivity of NLTE corrections to model atmosphere structure. Table 3 compares our NLTE corrections for selected models with the NLTE corrections determined by Osorio & Barklem (2016). The agreement is good.…”

Section: Resultsmentioning

confidence: 75%

“…We can test the corresponding errors in ∆A(Mg) by assuming that the uncertainty of the T (τ ) relationship can be approximated by a systematic shift in T eff . This is, of course, not a fully correct assumption, because also the Osorio & Barklem (2016). The data were computed using 1D hydrostatic model atmospheres, MAFAGS-OS in this work and MARCS in Osorio & Barklem (2016).…”

Section: Resultsmentioning

confidence: 99%

“…This is, of course, not a fully correct assumption, because also the Osorio & Barklem (2016). The data were computed using 1D hydrostatic model atmospheres, MAFAGS-OS in this work and MARCS in Osorio & Barklem (2016).…”

Section: Resultsmentioning

confidence: 99%

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Non-local Thermodynamic Equilibrium Stellar Spectroscopy with 1D and Models. I. Methods and Application to Magnesium Abundances in Standard Stars

Bergemann

Collet

Amarsi

et al. 2017

ApJ

104

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We determine Mg abundances in 6 Gaia benchmark stars using theoretical one-dimensional (1D) hydrostatic model atmospheres, as well as temporally-and spatially-averaged 3D model atmospheres ( 3D ). The stars cover a range of T eff from 4700 to 6500 K, log g from 1.6 to 4.4 dex, and [Fe/H] from −3.0 dex to solar. Spectrum synthesis calculations are performed in local thermodynamic equilibrium (LTE) and in non-LTE (NLTE) using the oscillator strengths recently published by Pehlivan Rhodin et al. We find that: a) Mg abundances determined from the infrared spectra are as accurate as the optical diagnostics, b) the NLTE effects on Mg i line strengths and abundances in this sample of stars are minor (although for a few Mg i lines the NLTE effects on abundance exceed 0.6 dex in 3D and 0.1 dex in 1D, c) the solar Mg abundance is 7.56 ± 0.05 dex (total error), in the excellent agreement with the Mg abundance measured in CI chondritic meteorites, d) the 1D NLTE and 3D NLTE approach can be used with confidence to analyse optical Mg i lines in spectra of dwarfs and sub-giants, but for red giants the Mg i 5711Å line should be preferred, e) lowexcitation Mg i lines are sensitive to the atmospheric structure; for these lines, LTE calculations with 3D models lead to significant systematic abundance errors. The methods developed in this work will be used to study Mg abundances of a large sample of stars in the next paper in the series.

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Section: Resultsmentioning

confidence: 75%

Section: Resultsmentioning

confidence: 99%

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Non-local Thermodynamic Equilibrium Stellar Spectroscopy with 1D and Models. I. Methods and Application to Magnesium Abundances in Standard Stars

Bergemann

Collet

Amarsi

et al. 2017

ApJ

104

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“…This enhances the role that inelastic hydrogen collision rates can play for a NLTE abundance determination. Recently, it has been shown that the chargetransfer (i.e., ion-pair production 4 ) processes can domi-nate over excitation processes (Osorio et al 2015;Osorio & Barklem 2016;Ezzeddine et al 2016b). Cross-section calculations for Li+H and Na+H (Barklem et al 2010), for example, have shown that the largest cross sections for excitation are small compared with those for ion-pair production from certain energy states.…”

Section: Iron Model Atommentioning

confidence: 99%

Ultra-metal-poor Stars: Spectroscopic Determination of Stellar Atmospheric Parameters Using Iron Non-LTE Line Abundances

Ezzeddine

Frebel

Plez

2017

ApJ

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We present new ultra-metal-poor (UMP) stars parameters with [Fe/H] < −4.0 based on line-by-line non-local thermodynamic equilibrium (NLTE) abundances using an up-to-date iron model atom with a new recipe for non-elastic hydrogen collision rates. We study the departures from LTE in their atmospheric parameter and show that they can grow up to ∼ 1.00 dex in [Fe/H], ∼ 150 K in T eff and ∼ 0.5 dex in log g toward the lowest metallicities. Accurate NLTE atmospheric stellar parameters, in particular [Fe/H] being significantly higher, are the first step to eventually providing full NLTE abundance patterns that can be compared with Population III supernova nucleosynthesis yields to derive properties of the first stars. Overall, this maximizes the potential of these likely secondgeneration stars to investigate the early universe and how the chemical elements were formed.

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“…There are several studies on NLTE analysis of neutral magnesium including the recent studies of Bergemann et al (2015), Osorio & Barklem (2016). The former studied NLTE effects in the J-band Mg i lines and, due to a lack of experimental log(g f ) values, calculated log(g f ) values were used.…”

Section: Introductionmentioning

confidence: 99%

Experimental and theoretical oscillator strengths of Mg i for accurate abundance analysis

Rhodin

Hartman

Nilsson

et al. 2017

A&A

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Context. With the aid of stellar abundance analysis, it is possible to study the galactic formation and evolution. Magnesium is an important element to trace the α-element evolution in our Galaxy. For chemical abundance analysis, such as magnesium abundance, accurate and complete atomic data are essential. Inaccurate atomic data lead to uncertain abundances and prevent discrimination between different evolution models. Aims. We study the spectrum of neutral magnesium from laboratory measurements and theoretical calculations. Our aim is to improve the oscillator strengths ( f -values) of Mg i lines and to create a complete set of accurate atomic data, particularly for the near-IR region.Methods. We derived oscillator strengths by combining the experimental branching fractions with radiative lifetimes reported in the literature and computed in this work. A hollow cathode discharge lamp was used to produce free atoms in the plasma and a Fourier transform spectrometer recorded the intensity-calibrated high-resolution spectra. In addition, we performed theoretical calculations using the multiconfiguration Hartree-Fock program ATSP2K.Results. This project provides a set of experimental and theoretical oscillator strengths. We derived 34 experimental oscillator strengths. Except from the Mg i optical triplet lines (3p 3 P• 0,1,2 -4s 3 S 1 ), these oscillator strengths are measured for the first time. The theoretical oscillator strengths are in very good agreement with the experimental data and complement the missing transitions of the experimental data up to n = 7 from even and odd parity terms. We present an evaluated set of oscillator strengths, gf, with uncertainties as small as 5%. The new values of the Mg i optical triplet line (3p 3 P• 0,1,2 -4s 3 S 1 ) oscillator strength values are ∼0.08 dex larger than the previous measurements.

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Mg line formation in late-type stellar atmospheres

Cited by 56 publications

References 32 publications

Non-local Thermodynamic Equilibrium Stellar Spectroscopy with 1D and Models. I. Methods and Application to Magnesium Abundances in Standard Stars

Non-local Thermodynamic Equilibrium Stellar Spectroscopy with 1D and Models. I. Methods and Application to Magnesium Abundances in Standard Stars

Ultra-metal-poor Stars: Spectroscopic Determination of Stellar Atmospheric Parameters Using Iron Non-LTE Line Abundances

Experimental and theoretical oscillator strengths of Mg i for accurate abundance analysis

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