First stars V - Abundance patterns from C to Zn and supernova yields in the early Galaxy

By R. Cayrel, É. Depagne, M. Spite, V. Hill, F. Spite, P. François, B. Plez, Timothy C. Beers, F. Primas, J. Andersen and 4 more. 2003

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In the framework of the ESO Large Programme "First Stars", very high-quality spectra of some 70 very metal-poor dwarfs and giants were obtained with the ESO VLT and UVES spectrograph. These stars are likely to have descended from the first generation(s) of stars formed after the Big Bang, and their detailed composition provides constraints on issues such as the nature of the first supernovae, the efficiency of mixing processes in the early Galaxy, the formation and evolution of the halo of the Galaxy, and the possible sources of reionization of the Universe. This paper presents the abundance analysis of an homogeneous sample of 35 giants selected from the HK survey of Beers et al. (1992, 1999), emphasizing stars of extremely low metallicity: 30 of our 35 stars are in the range −4.1 < (Fe/H) < −2. 7, and 22 stars have (Fe/H) < −3.0. Our new VLT/UVES spectra, at a resolving power of R ∼ 45 000 and with signal-to-noise ratios of 100-200 per pixel over the wavelength range 330-1000 nm, are greatly superior to those of the classic studies of McWilliam et al. (1995) and Ryan et al. (1996). The immediate objective of the work is to determine precise, comprehensive, and homogeneous element abundances for this large sample of the most metal-poor giants presently known. In the analysis we combine the spectral line modeling code "Turbospectrum" with OSMARCS model atmospheres, which treat continuum scattering correctly and thus allow proper inter- pretation of the blue regions of the spectra, where scattering becomes important relative to continuous absorption ( λ< 400 nm). We obtain detailed information on the trends of elemental abundance ratios and the star-to-star scatter around those trends, en- abling us to separate the relative contributions of cosmic scatter and observational/analysis errors. Abundances of 17 elements from C to Zn have been measured in all stars, including K and Zn, which have not previously been detected in stars with (Fe/H) < −3.0. Among the key results, we discuss the oxygen abundance (from the forbidden (OI) line), the different and sometimes complex trends of the abundance ratios with metallicity, the very tight relationship between the abundances of certain elements (e.g., Fe and Cr), and the high (Zn/Fe) ratio in the most metal-poor stars. Within the error bars, the trends of the abundance ratios with metallicity are consistent with those found in earlier literature, but in many cases the scatter around the average trends is much smaller than found in earlier studies, which were limited to lower-quality spectra. We find that the cosmic scatter in several element ratios may be as low as 0.05 dex. The evolution of the abundance trends and scatter with declining metallicity provides strong constraints on the yields of the first supernovae and their mixing into the early ISM. The abundance ratios found in our sample do not match the predicted yields from pair-instability hypernovae, but are consistent with element production by super- novae with progenitor masses up to 100 M� . Moreover, the composition of the ejecta that have enriched the matter

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CORE-COLLAPSE SUPERNOVAE FROM 9 TO 120 SOLAR MASSES BASED ON NEUTRINO-POWERED EXPLOSIONS (2015, background): “This is surprising given that only a minor fraction of iron-group elements is expected to come from massive stars (e.g., Timmes et al. 1995; Cayrel et al. 2004).”
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).”
Spectral models for solar-scaled and α-enhanced stellar populations (2007, background): “…for ellipticals, highresolution stellar spectroscopy also suggests low values of [Ca/Fe] (e.g. Zoccali et al. 2004; Alves-Brito et al. 2006), while in the metal-poor population of our Galaxy the Ca is overabundant, following the trend of the other light elements (e.g. Cayrel et al. 2004).”
First stars VII - Lithium in extremely metal poor dwarfs (2006, methodology): “13 of Cayrel et al. 2004).”
Chemical Evolution in Hierarchical Models of Cosmic Structure. I. Constraints on the Early Stellar Initial Mass Function (2005, background): “…galaxies for comparison to HST and JWST data at z > 6, and (2) a model distribution of metal-poor Galactic stars for comparison to the existing samples (Cayrel et al. 2004; Cohen et al. 2004) and eventually to the thousands of metal-poor halo stars expected from large future surveys (SEGUE, WFMOS).”
THE RADIAL VELOCITY EXPERIMENT (RAVE): FIFTH DATA RELEASE (2013, methodology): “This corrected the metallicity offsets with the external datasets of Pasquini et al. (2004); Pancino et al. (2010); Cayrel et al. (2004); Ruchti et al. (2011) and the PASTEL database (Soubiran et al. 2010).”
THE MASS SPECTRUM OF THE FIRST STARS (2014, background): “(A color version of this figure is available in the online journal.) patterns of the extremely metal-poor stars with [Fe/H] ∼ −3 (BD –18:5550, CS 29502–042, CS 29516–024, and CS 31082–001, Cayrel et al. 2004)10 and DLA systems (Cooke et al. 2011).”
Neutron-Capture Elements in the Early Galaxy (2008, methodology): “The very small star-to-star scatter in particular has been emphasized by Cayrel et al. (2004) and Arnone et al. (2005).”
The s process: Nuclear physics, stellar models, and observations (2010, neutral): “Assuming that SNII produce about 1/3 of solar Fe, this means that the ratio [Zn/Fe] in the Halo should be a bit positive, about 0.2 dex on average, consistent with spectroscopic observations (e.g. Cayrel et al., 2004).”
Non-LTE calculations for neutral Na in late-type stars using improved atomic data (2011, background): “Moreover, almost solar values are obtained from non-LTE analysis of extremely metal-poor stars below [Fe/H] < −3.0, where LTE analysis, at least of giants, instead yields positive ratios, [Na/Fe] ≈ 0.3 (Cayrel et al. 2004; Andrievsky et al. 2007).”
Stellar Abundances for the Galactic Archeology (SAGA) Database — Compilation of the Characteristics of Known Extremely Metal-Poor Stars (2008, background): “…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. 2005; Jonsell et al. 2005; Aoki et…”
Abundances of Baade’s Window Giants from Keck HIRES Spectra. II. The Alpha and Light Odd Elements (2006, background): “…agreement between F00 thick disk giant abundances and literature values from dwarf stars; this, and the similarity of the mean F00 [<SiCaTiI>/Fe] value with the Cayrel et al. (2004)extreme metal-poor halo stars, suggests that there are no serious zero-point problems with the F00 halo abundances.”
Very low-metallicity massive stars: - Pre-SN evolution models and primary nitrogen production (2006, background): “Precise measurements of surface abundances of extremely metal-poor (EMP) stars have recently been obtained by Cayrel et al. (2004), Spite et al. (2005), and Israelian et al. (2004a).”
Quantifying the uncertainties of chemical evolution studies II. Stellar yields (2010, background): “Observations of stars in the solar vicinity show that [Zn/Fe] is close to zero for metallicities in the interval−2.0 < [Fe/H] < +0.4 (e.g. Bensby et al. 2005; Nissen et al. 2007), but rises steeply to [Zn/Fe] ≈ +0.5 at the lowest metallicities (Cayrel et al. 2004).”
CHEMICAL EVOLUTION IN HIERARCHICAL MODELS OF COSMIC STRUCTURE. II. THE FORMATION OF THE MILKY WAY STELLAR HALO AND THE DISTRIBUTION OF THE OLDEST STARS (2009, background): “That metal-poor stars1 address the first stars has been taken for granted as a working hypothesis by many observational programs (Cayrel et al. 2004; Christlieb et al. 2002; Frebel et al. 2005).”
Probing the formation of the first low‐mass stars with stellar archaeology (2007, background): “This scenario suggests an explanation for the observed lack of scatter in the abundance ratios of homogeneously analysed low metallicity stars (Cayrel et al. 2004; see also Karlsson & Gustafsson 2005).”