Abundances of 30 Elements in 23 Metal-Poor Stars

By Jennifer A. Johnson. 2001

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We report the abundances of 30 elements in 23 metal-poor ([Fe/H] < -1.7) giants. These are based on 7774 equivalent widths and spectral synthesis of 229 additional lines. Hyperfine splitting is taken into account when appropriate. Our choice of model atmospheres has the most influence on the accuracy of our abundances. We consider the effect of different model atmospheres on our results. In addition to the random errors in Teff, log g, and microturbulent velocity, there are several sources of systematic error. These include using Teff determined from Fe I lines rather than colors, ignoring non-LTE effects on the Fe I/Fe II ionization balance, using models with solar [α/Fe] ratios, and using Kurucz models with overshooting. Of these, only the use of models with solar [α/Fe] ratios had a negligible effect. However, while the absolute abundances can change by greater than 0.10 dex, the relative abundances, especially between closely allied atoms such as the rare earth group, often show only small (less than 0.03 dex) changes. We found that some strong lines of Fe I, Mn I, and Cr I consistently gave lower abundances by ∼0.2 dex, a number larger than the quoted errors in the gf-values. After considering a model with depth-dependent microturbulent velocity and a model with hotter temperatures in the upper layers, we conclude that the latter did a better job of resolving the problem and agreeing with observational evidence for the structure of stars. The error analysis includes the effects of correlation of Teff, log g, and ξ errors, which is crucial for certain element ratios, such as [Mg/Fe]. The abundances presented here are being analyzed and discussed in a separate series of papers.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/4adb2a1a9ed336539df8415444869bee4adc4333

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Citations in the corpus

Abundances in Stars from the Red Giant Branch Tip to Near the Main-Sequence Turnoff in M71. III. Abundance Ratios (2001, background): “Our pred ignores covariance among the error terms, which is discussed in detail by Johnson (2002).”
THE CHEMICAL EVOLUTION OF THE DRACO DWARF SPHEROIDAL GALAXY (2009, background): “The figure shows good agreement between the 0Z and First Stars Project abundance ratios for this element; [Si/Fe] from Johnson (2002) is again slightly high.”
The Rise of the s-Process in the Galaxy (2004, methodology): “There is only a small offset between [Fe II/H] values derived in this study and those found in Burris et al. (2000) and Johnson (2002), as shown in Fig.”
The Hamburg/ESO R-process enhanced star survey (HERES) - III. HE 0338-3945 and the formation of the r + s stars (2006, background): “Such a discrepancy has also been noticed by Johnson (2002).”
THE MOST METAL-POOR STARS. IV. THE TWO POPULATIONS WITH [Fe/H] ≲ −3.0 (2012, background): “…trends for most elements), there exist chemically peculiar stars (those with strong enhancements or deficiencies of particular elements) (see e.g., McWilliam et al. 1995; Ryan et al. 1996; Norris et al. 2001; Johnson 2002; Cayrel et al. 2004; Cohen et al. 2008; Lai et al. 2008; Yong et al. 2012).”
THE MOST METAL-POOR STARS. II. CHEMICAL ABUNDANCES OF 190 METAL-POOR STARS INCLUDING 10 NEW STARS WITH [Fe/H] ⩽ −3.5,, (2012, methodology): “…Research, School of Physics, Astronomy & Mathematics, University of Hertfordshire, College Lane,Hatfield, Hertfordshire, AL10 9AB, UK; s.g.ryan@herts.ac.uk 1996; Norris et al. 2001; Johnson 2002; Cayrel et al. 2004; Beers & Christlieb 2005; Cohen et al. 2008; Lai et al. 2008; Frebel & Norris 2011).”
Stellar Abundances for the Galactic Archeology (SAGA) Database — Compilation of the Characteristics of Known Extremely Metal-Poor Stars (2008, background): “…Fulbright 2000; Preston & Sneden 2000; Burris et al. 2000; Mishenina & Kovtyukh 2001; Aoki et al. 2002; Cohen et al. 2002; Carretta et al. 2002; Johnson 2002; Nissen et al. 2002; Cayrel et al. 2004; Honda et al. 2004; Cohen et al. 2004; Simmerer et al. 2004; Spite et al. 2005; Barklem et al.…”
DETAILED CHEMICAL ABUNDANCES IN THE r-PROCESS-RICH ULTRA-FAINT DWARF GALAXY RETICULUM 2 (2016, background): “We simultaneously require no correlation between these abundances and the line strength, which sets vt. Spectroscopic Teff values like these are known to be systematically cooler by a few percent than those derived from color-Teff relations (e.g., Johnson 2002).”
Neutron-Capture Elements in the Early Galaxy (2008, methodology): “Most of the r-process data are from Barklem et al. (2005), with the addition of data from Westin et al. (2000), Cowan et al. (2002), Hill et al. (2002), Johnson (2002), Sneden et al. (2003), Honda et al. (2004), Ivans et al. (2006), and Frebel et al. (2007).”
THE ABUNDANCES OF NEUTRON-CAPTURE SPECIES IN THE VERY METAL-POOR GLOBULAR CLUSTER M15: A UNIFORM ANALYSIS OF RED GIANT BRANCH AND RED HORIZONTAL BRANCH STARS (2011, methodology): “It was then necessary to modify the MOOG program as the LTE approximation was no longer sufficient (this has also been remarked upon by other abundance surveys, e.g. Johnson 2002(50) and Cayrel et al. 2004(20)).”
First stars V - Abundance patterns from C to Zn and supernova yields in the early Galaxy (2003, result): “Using the photometrically derived Teff we find no trend with the excitation of Fe I lines (at least when only the lines with χex > 1eV are taken into account), contrary to what was reported by Johnson (2002) using Kurucz models.”
Helioseismology and Solar Abundances (2007, background): “Errors and uncertainties in spectroscopic techniques to determine stellar spectra have been discussed by Johnson (2002).”
MULTI-ELEMENT ABUNDANCE MEASUREMENTS FROM MEDIUM-RESOLUTION SPECTRA. II. CATALOG OF STARS IN MILKY WAY DWARF SATELLITE GALAXIES (2010, background): “Our measurements of Teff are typically ∼ 100 K below those of Johnson (2002) and ∼ 100 K above those of Lai et al. (2004, 2007).”
Abundances In Very Metal-Poor Dwarf Stars (2004, background): “The surveys included are Cayrel et al. (2003), McWilliam et al. (1995), Fulbright (2000), Norris, Ryan & Beers (2001), Johnson (2002), Ryan, Norris & Beers (1996), Gratton & Sneden (2001) and Nissen et al. (2000).”
Abundances in giant stars of the globular cluster NGC 6752 (2005, unknown): “Our uncertainties also do not take into account covariance terms which are discussed by McWilliam et al. (1995) and Johnson (2002).”
Chemodynamics of the Milky Way - I. The first year of APOGEE data (2013, background): “It is known that systematic differences between the photometric and spectroscopic temperature scales exist: spectroscopic »excitation temperatures« often yield lower values than colour–temperature calibrations by a few hundred Kelvins (e.g., Johnson 2002).”