C.D.S. - SIMBAD4 rel 1.7 - 2020.02.20CET11:30:44

2010A&A...511A..47H - Astronomy and Astrophysics, volume 511, A47-47 (2010/2-2)

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


Abstract (from CDS):

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. 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. Using the code MULTI we calculate NLTE corrections to the LTE abundances for the FeI lines measured in the six stars, and determine new Teff's. We keep other physical parameters, i.e. logg, [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. (1999ApJ...523..654R), the infrared flux method (IRFM) temperatures of Melendez & Ramirez (2004ApJ...615L..33M), and the Balmer line wing temperatures of Asplund et al. (2006ApJ...644..229A). We find that our temperatures are hotter than both the Ryan et al. and Asplund et al. temperatures by typically ∼110-160K, but are still cooler than the temperatures of Melendez & Ramirez (2004ApJ...615L..33M) by typically ∼190K. The temperatures imply a primordial Li abundance of 2.19dex or 2.21dex, depending on the magnitude of collisions with hydrogen in the calculations, still well below the value of 2.72dex inferred from WMAP + BBN. We discuss the effects of collisions on trends of [][7]Li 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.

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Journal keyword(s): Galaxy: halo - early Universe - stars: abundances - stars: atmospheres - line: formation - radiative transfer

Simbad objects: 6

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Number of rows : 6

N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2020
1 CD-33 1173 Pe* 03 19 35.3161303154 -32 50 43.157841051   11.272 10.902 10.421 10.152 CEMP 45 0
2 HD 74000 PM* 08 40 50.8038415228 -16 20 42.513275817 9.84 10.09 9.66     F2 242 0
3 HD 84937 PM* 09 48 56.09801 +13 44 39.3237 8.49 8.68 8.32 7.97 7.70 F8Vm-5 713 0
4 BD+26 2621 PM* 14 54 10.7124388855 +25 33 48.928656234   11.40   10.7   F0 32 0
5 HD 140283 Pe* 15 43 03.0967798658 -10 56 00.595803430 7.508 7.711 7.212 6.63 8.21 F9VkA5mA1 848 0
6 LP 815-43 PM* 20 38 13.2997980664 -20 26 10.852305467   11.31 10.72     ~ 64 0

    Equat.    Gal    SGal    Ecl

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