First stars XII. Abundances in extremely metal-poor turnoff stars,and comparison with the giants

By P. Bonifacio, M. Spite, R. Cayrel, V. Hill, F. Spite, P. François, B. Plez, H. Ludwig, E. Caffau, P. Molaro and 14 more. 2009

171 citations recorded by the source corpus.

Context. The detailed chemical abundances of extremely metal-poor (EMP) stars are key guides to understanding the early chemical evolution of the Galaxy. Most existing data, however, treat giant stars that may have experienced internal mixing later. Aims. We aim to compare the results for giants with new, accurate abundances for all observable elements in 18 EMP turno. stars. Methods. VLT/UVES spectra at R similar to 45 000 and S/N similar to 130 per pixel (lambda lambda 330-1000 nm) are analysed with OSMARCS model atmospheres and the TURBOSPECTRUM code to derive abundances for C, Mg, Si, Ca, Sc, Ti, Cr, Mn, Co, Ni, Zn, Sr, and Ba. Results. For Ca, Ni, Sr, and Ba, we find excellent consistency with our earlier sample of EMP giants, at all metallicities. However, our abundances of C, Sc, Ti, Cr, Mn and Co are similar to 0.2 dex larger than in giants of similar metallicity. Mg and Si abundances are similar to 0.2 dex lower (the giant [Mg/Fe] values are slightly revised), while Zn is again similar to 0.4 dex higher than in giants of similar [Fe/H] (6 stars only). Conclusions. For C, the dwarf/giant discrepancy could possibly have an astrophysical cause, but for the other elements it must arise from shortcomings in the analysis. Approximate computations of granulation (3D) effects yield smaller corrections for giants than for dwarfs, but suggest that this is an unlikely explanation, except perhaps for C, Cr, and Mn. NLTE computations for Na and Al provide consistent abundances between dwarfs and giants, unlike the LTE results, and would be highly desirable for the other discrepant elements as well. Meanwhile, we recommend using the giant abundances as reference data for Galactic chemical evolution models.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/0ddd17eca01f175e8639392983c373bd772f891e

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In Astronomy and Astrophysics

1. Timothy C. Beers
2. A. Frebel
3. J. Norris
4. C. Sneden
5. Martin Asplund
6. N. Christlieb
7. Wak Aoki
8. A. Karakas

In Instrumentation

1. Timothy C. Beers
2. A. Frebel
3. J. Norris
4. C. Sneden
5. Martin Asplund
6. Wak Aoki
7. N. Christlieb
8. I. Thompson

Citations in the corpus

• Quantifying the uncertainties of chemical evolution studies II. Stellar yields (2010, background): “Several authors (e.g. Honda et al. 2004; Lai et al. 2008; Bonifacio et al. 2009) have noticed that an offset exists between the abundances derived from Cr I and Cr II lines.”
• THE MOST METAL-POOR STARS. IV. THE TWO POPULATIONS WITH [Fe/H] ≲ −3.0 (2012, unknown): “…−3.39 0.27 0 1 11920 CS 22965-054 6137 3.68 −3.10 0.62 –283 4 2300 CS 29502-042 5039 2.09 −3.27 0.16 –138 1 3470 CS 22888-031 6241 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),…”
• THE MOST METAL-POOR STARS. II. CHEMICAL ABUNDANCES OF 190 METAL-POOR STARS INCLUDING 10 NEW STARS WITH [Fe/H] ⩽ −3.5,, (2012, methodology): “The reason for separating the dwarfs from giants is that we want to compare, as best we can, stars with similar stellar parameters to minimize systematic errors (e.g., Cayrel et al. 2004; Meléndez et al. 2008; Bonifacio et al. 2009; Alves-Brito et al. 2010; Nissen & Schuster 2010)16.”
• A SEARCH FOR STARS OF VERY LOW METAL ABUNDANCE. VI. DETAILED ABUNDANCES OF 313 METAL-POOR STARS (2014, methodology): “…abundance versus E.P. as the primary means of determining Teff b Studies that use Fe i abundance versus E.P. as the primary means of determining Teff (2004), Honda et al. (2004b), Preston et al. (2006a), Lai et al. (2008), Bonifacio et al. (2009), Ishigaki et al. (2010), and Roederer et al. (2010).”
• HIGH-RESOLUTION SPECTROSCOPY OF EXTREMELY METAL-POOR STARS FROM SDSS/SEGUE. I. ATMOSPHERIC PARAMETERS AND CHEMICAL COMPOSITIONS (2012, background): “Previous studies of large samples of candidate metal-poor stars from these surveys have revealed the chemical compositions of stars with [Fe/H]∼ −3 (Cayrel et al. 2004; Cohen et al. 2004; Honda et al. 2004; Barklem et al. 2005; Aoki et al. 2005; Lai et al. 2008; Bonifacio et al. 2009).”