First stars VII - Lithium in extremely metal poor dwarfs

By P. Bonifacio, P. Molaro, T. Sivarani, R. Cayrel, M.Spite, F. Spite, B. Plez, J. Andersen, B. Barbuy, Timothy C. Beers and 17 more. 2006

176 citations recorded by the source corpus.

Context. The primordial lithium abundance is a key prediction of models of big bang nucleosynthesis, and its abundance in metal-poor dwarfs (the Spite plateau) is an important, independent observational constraint on such models. Aims. This study aims to determine the level and constancy of the Spite plateau as definitively as possible from homogeneous highquality VLT-UVES spectra of 19 of the most metal-poor dwarf stars known. Methods. Our high-resolution (R ∼ 43 000), high S /N spectra are analysed with OSMARCS 1D LTE model atmospheres and turbospectrum synthetic spectra to determine effective temperatures, surface gravities, and metallicities, as well as Li abundances for our stars. Results. Eliminating a cool subgiant and a spectroscopic binary, we find 8 stars to have −3.5 < [Fe/H] < −3. 0a nd 9s tars with −3.0 < [Fe/H] < −2.5. Our best value for the mean level of the plateau is A(Li) = 2.10 ± 0.09. The scatter around the mean is entirely explained by our estimate of the observational error and does not allow for any intrinsic scatter in the Li abundances. In addition, we conclude that a systematic error of the order of 200 K in any of the current temperature scales remains possible. The iron excitation equilibria in our stars support our adopted temperature scale, which is based on a fit to wings of the Hα line, and disfavour hotter scales, which would lead to a higher Li abundance, but fail to achieve excitation equilibrium for iron. Conclusions. We confirm the previously noted discrepancy between the Li abundance measured in extremely metal-poor turnoff stars and the primordial Li abundance predicted by standard Big-Bang nucleosynthesis models adopting the baryonic density inferred from WMAP. We discuss recent work explaining the discrepancy in terms of diffusion and find that uncertain temperature scales remain a major question.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/247e7b7ae8976fd66b18f0a8d20df6298e4861f1

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In Astronomy and Astrophysics

1. Martin Asplund
2. Timothy C. Beers
3. A. Frebel
4. J. Norris
5. I. Ramírez
6. Luca Casagrande
7. C. Sneden
8. K. Lind

In Instrumentation

1. Martin Asplund
2. A. Frebel
3. J. Norris
4. Timothy C. Beers
5. I. Ramírez
6. K. Lind
7. Luca Casagrande
8. V. Hill

Citations in the corpus

• The Primordial Abundance of 4He: A Self-consistent Empirical Analysis of Systematic Effects in a Large Sample of Low-Metallicity H II Regions (2007, result): “…He i emissivities is much higher than the value of bh 2 derived from the primordial 7Li abundance (Bonifacio & Molaro 1997; Asplund et al. 2006; Bonifacio et al. 2007) but is in excellent agreement with the value of bh 2 ¼ 0:021 0:002 derived from recent measurements of the deuterium…”
• A new implementation of the infrared flux method using the 2MASS catalogue (2009, methodology): “We completed the sample with extremely metal-poor dwarfs from Bonifacio et al. (2007), Christlieb et al. (2004), and Barklem et al. (2005).”
• Departures from LTE for neutral Li in late-type stars (2009, background): “For recent studies of lithium in halo field stars see e.g. Ryan et al. (2001), Charbonnel & Primas (2005), Asplund et al. (2006), Bonifacio et al. (2007), and Hosford et al. (2009).”
• An absolutely calibrated T eff scale from the infrared flux method. Dwarfs and subgiants (2010, methodology): “To investigate the metal-poor end of the Teff scale in more detail, stars with reliable input data from Ramı́rez & Meléndez (2005a), Bonifacio et al. (2007) and Aoki et al. (2009) were added.”
• Near-Field Cosmology with Extremely Metal-Poor Stars (2015, methodology): “We refer the reader to Thorburn (1994), Ryan, Norris & Beers (1999), Charbonnel & Primas (2005), Asplund et al. (2006), Bonifacio et al. (2007), Aoki et al. (2009b), Meléndez et al. (2010), Sbordone et al. (2010), Bonifacio et al. (2012b), and references therein, for details of some of the…”
• Atomic Diffusion and Mixing in Old Stars. I. Very Large Telescope FLAMES-UVES Observations of Stars in NGC 6397 (2007, background): “Increasing TOP-star effective temperatures by 100K to remove the abundance trends, as claimed by Bonifacio et al. (2007), is not possible.”
• First stars XII. Abundances in extremely metal-poor turnoff stars,and comparison with the giants (2009, background): “Details are given in “First Stars VII”, together with an extensive discussion of the effective temperature scale.”
• THE MOST METAL-POOR STARS. IV. THE TWO POPULATIONS WITH [Fe/H] ≲ −3.0 (2012, unknown): “…4.47 −3.31 0.38 –125 6 940 CS 22952-015 4824 1.50 −3.44 −0.41 –18 1 7890 a References: 1 = Bonifacio et al. (2009), 2 = Honda et al. (2004a), 3 = Cohen et al. (2008), 4 = Lai et al. (2008), 5 = Caffau et al. (2011), 6 = Bonifacio et al. (2007), 7= Norris et al. (2012b) b SDSS J102915+172927…”
• Signatures of intrinsic Li depletion and Li-Na anti-correlation in the metal-poor globular cluster NGC 6397 , (2009, background): “…for stellar metallicities [Fe/H] = (−3.5) − (−1.0), with a possible tendency toward increasing Li abundance with increasing metallicity (e.g. Ryan et al. 2001; Meléndez & Ramı́rez 2004; Charbonnel & Primas 2005; Asplund et al. 2006; Bonifacio et al. 2007a; Hosford et al. 2009; Aoki et al. 2009).”
• Varying Constants, Gravitation and Cosmology (2010, background): “50)× 10−10 and its values measured in metal-poor halo stars in our galaxy [63], (7)Li/H =”