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Lithium abundances of halo dwarfs based on excitation temperatures. II. Non-local thermodynamic equilibrium

Hosford, A.; Garcia Perez, Ana; Collet, R; Ryan, S. G.; Norris, John; Olive, Keith

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Context: The plateau in the abundance of 7Li in metal-poor stars was initially interpreted as an observational indicator of the primordial lithium abundance. However, this observational value is in disagreement with that deduced from calculations of Big Bang nucleosynthesis (BBN), when using the Wilkinson microwave anisotropy probe (WMAP) baryon density measurements. One of the most important factors in determining the stellar lithium abundance is the effective temperature. In a previous study...[Show more]

dc.contributor.authorHosford, A.
dc.contributor.authorGarcia Perez, Ana
dc.contributor.authorCollet, R
dc.contributor.authorRyan, S. G.
dc.contributor.authorNorris, John
dc.contributor.authorOlive, Keith
dc.date.accessioned2015-12-08T22:46:13Z
dc.identifier.issn0004-6361
dc.identifier.urihttp://hdl.handle.net/1885/38050
dc.description.abstractContext: The plateau in the abundance of 7Li in metal-poor stars was initially interpreted as an observational indicator of the primordial lithium abundance. However, this observational value is in disagreement with that deduced from calculations of Big Bang nucleosynthesis (BBN), when using the Wilkinson microwave anisotropy probe (WMAP) baryon density measurements. One of the most important factors in determining the stellar lithium abundance is the effective temperature. In a previous study by the authors, new effective temperatures (Teff) for sixteen metal-poor halo dwarfs were derived using a local thermodynamic equilibrium (LTE) description of the formation of Fe lines. This new Teff scale reinforced the discrepancy. Aims: For six of the stars from our previous study we calculate revised temperatures using a non-local thermodynamic equilibrium (NLTE) approach. These are then used to derive a new mean primordial lithium abundance in an attempt to solve the lithium discrepancy. Methods: Using the code MULTI we calculate NLTE corrections to the LTE abundances for the Fe i lines measured in the six stars, and determine new Teff's. We keep other physical parameters, i.e. log g, [Fe/H] and ξ, constant at the values calculated in Paper I. With the revised Teff scale we derive new Li abundances. We compare the NLTE values of Teff with the photometric temperatures of Ryan et al. (1999, ApJ, 523, 654), the infrared flux method (IRFM) temperatures of Meléndez & Ramírez (2004, ApJ, 615, L33), and the Balmer line wing temperatures of Asplund et al. (2006, ApJ, 644, 229). Results: We find that our temperatures are hotter than both the Ryan et al. and Asplund et al. temperatures by typically ∼110-160 K, but are still cooler than the temperatures of Meléndez & Ramírez by typically ∼190 K. The temperatures imply a primordial Li abundance of 2.19 dex or 2.21 dex, depending on the magnitude of collisions with hydrogen in the calculations, still well below the value of 2.72 dex inferred from WMAP + BBN. We discuss the effects of collisions on trends of 7Li abundances with [Fe/H] and Teff, as well as the NLTE effects on the determination of log g through ionization equilibrium, which imply a collisional scaling factor SH > 1 for collisions between Fe and H atoms.
dc.publisherSpringer
dc.sourceAstronomy and Astrophysics
dc.subjectKeywords: Early universe; Galaxy: halo; Line: formation; Stars: abundances; Stars: atmospheres; Bayesian networks; Chemical elements; Galaxies; Lithium; Radiative transfer; Stars; Thermodynamics; Temperature Early Universe; Galaxy: halo; Line: formation; Radiative transfer; Stars: abundances; Stars: atmospheres
dc.titleLithium abundances of halo dwarfs based on excitation temperatures. II. Non-local thermodynamic equilibrium
dc.typeJournal article
local.description.notesImported from ARIES
local.identifier.citationvolume511
dc.date.issued2010
local.identifier.absfor020110 - Stellar Astronomy and Planetary Systems
local.identifier.ariespublicationu3356449xPUB157
local.identifier.ariespublicationu4630950xPUB56
local.type.statusPublished Version
local.contributor.affiliationHosford, A., University of Hertfordshire
local.contributor.affiliationGarcia Perez, Ana, University of Hertfordshire
local.contributor.affiliationCollet, R, Max Planck Institute for Astrophysics
local.contributor.affiliationRyan, S. G., University of Hertfordshire
local.contributor.affiliationNorris, John, College of Physical and Mathematical Sciences, ANU
local.contributor.affiliationOlive, Keith, University of Minnesota
local.description.embargo2037-12-31
local.bibliographicCitation.issue1
local.bibliographicCitation.startpageA47
local.identifier.doi10.1051/0004-6361/200913693
local.identifier.absseo970102 - Expanding Knowledge in the Physical Sciences
dc.date.updated2016-02-24T09:54:00Z
local.identifier.scopusID2-s2.0-79952848340
local.identifier.thomsonID000275752400095
CollectionsANU Research Publications

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