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Ca line formation in late-type stellar atmospheres: I. The model atom
Inst Astrofis Canarias, Tenerife 38205, Spain;Univ La Laguna, E-38206 Tenerife, Spain.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Astrophysics. Max Plank Inst Astron, Konigstuhl 17, D-69117 Heidelberg, Germany.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Astrophysics.
Inst Astrofis Canarias, Tenerife 38205, Spain;Univ La Laguna, E-38206 Tenerife, Spain.
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2019 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 623, article id A103Article in journal (Refereed) Published
Abstract [en]

Context

Departures from local thermodynamic equilibrium (LTE) distort the calcium abundance derived from stellar spectra in various ways, depending on the lines used and the stellar atmospheric parameters. The collection of atomic data adopted in non-LTE (NLTE) calculations must be sufficiently complete and accurate.

Aims

We derive NLTE abundances from high-quality observations and reliable stellar parameters using a model atom built afresh for this work, and check the consistency of our results over a wide wavelength range with transitions of atomic and singly ionised calcium.

Methods

We built and tested Cat and Can model atoms with state-of-the-art radiative and collisional data, and tested their performance deriving the Ca abundance in three benchmark stars: Procyon, the Sun, and Arcturus. We have excellent-quality observations and accurate stellar parameters for these stars. Two methods to derive the LTE/NLTE abundances were used and compared. The LTE/NLTE centre-to-limb variation (CLV) of Ca lines in the Sun was also investigated.

Results

The two methods used give similar results in all three stars. Several discrepancies found in LTE do not appear in our NLTE results; in particular the agreement between abundances in the visual and infra-red (IR) and the Cat and Can ionisation balance is improved overall, although substantial line-to-line scatter remains. The CLV of the calcium lines around 6165 angstrom can be partially reproduced. We suspect differences between our modelling and CLV results are due to inhomogeneities in the atmosphere that require 3D modelling.

Place, publisher, year, edition, pages
2019. Vol. 623, article id A103
Keywords [en]
line: formation, stars: abundances
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:uu:diva-380454DOI: 10.1051/0004-6361/201834680ISI: 000460891400001OAI: oai:DiVA.org:uu-380454DiVA, id: diva2:1299863
Funder
Swedish Research Council, 2015-00415_3Knut and Alice Wallenberg FoundationSwedish Research CouncilAvailable from: 2019-03-28 Created: 2019-03-28 Last updated: 2019-03-28Bibliographically approved

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Lind, KarinBarklem, Paul S.

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