First stars VIII. Enrichment of the neutron-capture elements in the early Galaxy

By P. Francois, É. Depagne, V. Hill, M. Spite, F. Spite, B. Plez, Timothy C. Beers, J. Andersen, G. James, B. Barbuy and 5 more. 2007

252 citations recorded by the source corpus.

Context: Extremely metal-poor (EMP) stars in the halo of the Galaxy are sensitive probes of the production of the first heavy elements and the efficiency of mixing in the early interstellar medium. The heaviest measurable elements in such stars are our main guides to understanding the nature and astrophysical site(s) of early neutron-capture nucleosynthesis. Aims: Our aim is to measure accurate, homogeneous neutron-capture element abundances for the sample of 32 EMP giant stars studied earlier in this series, including 22 stars with [Fe/H]< -3.0. Methods: Based on high-resolution, high S/N spectra from the ESO VLT/UVES, 1D, LTE model atmospheres, and synthetic spectrum fits, we determine abundances or upper limits for the 16 elements Sr, Y, Zr, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, and Yb in all stars. Results: As found earlier, [Sr/Fe], [Y/Fe], [Zr/Fe] and [Ba/Fe] are below Solar in the EMP stars, with very large scatter. However, we find a tight anti-correlation of [Sr/Ba], [Y/Ba], and [Zr/Ba] with [Ba/H] for -4.5 <[Ba/H] < -2.5, also when subtracting the contribution of the main r-process as measured by [Ba/H]. Spectra of even higher S/N ratio are needed to confirm and extend these results below [Fe/H] ? -3.5. The huge, well-characterised scatter of the [n-capture/Fe] ratios in our EMP stars is in stark contrast to the negligible dispersion in the [ ?/Fe] and [Fe-peak/Fe] ratios for the same stars found in Paper V. Conclusions: These results demonstrate that a second (?weak? or LEPP) r-process dominates the production of the lighter neutron-capture elements for [Ba/H] < -2.5. The combination of very consistent [ ?/Fe] and erratic [n-capture/Fe] ratios indicates that inhomogeneous models for the early evolution of the halo are needed. Our accurate data provide strong constraints on future models of the production and mixing of the heavy elements in the early Galaxy. Based on observations made with the ESO Very Large Telescope at Paranal Observatory, Chile (program ID 165.N-0276(A); P.I: R. Cayrel).

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/f2b3c1138328535b0dba5c98203f7853cdc5d1f6

Citations in the corpus

• A SEARCH FOR STARS OF VERY LOW METAL ABUNDANCE. VI. DETAILED ABUNDANCES OF 313 METAL-POOR STARS (2014, unknown): “…represents the mean difference, standard deviation, and number of stars: 〈∆〉 (σ, N). a Includes [Ba/Fe] from McWilliam (1998) b Includes [C/Fe] and [N/Fe] from Spite et al. (2005) and [Sr/Fe] and [Ba/Fe] from François et al. (2007) lines of each species were employed in each star by each analysis.”
• THE MOST METAL-POOR STARS. II. CHEMICAL ABUNDANCES OF 190 METAL-POOR STARS INCLUDING 10 NEW STARS WITH [Fe/H] ⩽ −3.5,, (2012, unknown): “…SCALE In the context of elemental-abundance determinations in metal-poor stars, the FIRST STARS group (e.g., Cayrel et al. 2004; Spite et al. 2005; François et al. 2007; Bonifacio et al. 2009) obtained very high-quality spectra and conducted a careful analysis, such that their derived abundances…”
• 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, unknown): “…star data have been taken from these surveys: Fulbright (2000)(34), Reddy et al. (2003)(76), Cayrel et al. (2004)(20), Cohen et al. (2004)(22), Simmerer et al. (2004)(80), Barklem et al. (2005)(8), Reddy, Lambert & Allende Prieto (2006)(75), François et al. (2007)(31), and Lai et al. (2008)(59).”
• THE HISTORY OF R-PROCESS ENRICHMENT IN THE MILKY WAY (2014, unknown): “…observations, since there are many stars where the Eu 5 We also note that the [α/Fe] chemical evolution is poorly matched with this less efficient mixing prescription. abundance has not been measured (e.g., Barklem et al. 2005; François et al. 2007; Cohen et al. 2008; Roederer et al. 2010, 2014).”
• Stellar Abundances for the Galactic Archeology (SAGA) Database — Compilation of the Characteristics of Known Extremely Metal-Poor Stars (2008, unknown): “…2004; Spite et al. 2005; Barklem et al. 2005; Jonsell et al. 2005; Aoki et al. 2005; Garćıa Pérez & Primas 2006; Cohen et al. 2006; Aoki et al. 2007; François et al. 2007), there are no present databases that make these data readily available to astronomers and other researchers in order to…”
• THE CHEMICAL EVOLUTION OF THE DRACO DWARF SPHEROIDAL GALAXY (2009, unknown): “The Galactic halo field samples from the 0Z Project and the First Stars Project (data for Sr and Ba is from Francois et al 2007) overlap well for the abundance ratio [Sr/Fe] versus Fe-metallicity shown in Fig.”
• HIGH-RESOLUTION SPECTROSCOPY OF EXTREMELY METAL-POOR STARS IN THE LEAST EVOLVED GALAXIES: URSA MAJOR II and COMA BERENICES (2009, unknown): “François et al. (2007) find that the neutron-capture abundances generally decrease at the lowest Fe abundances, i.e., below [Fe/H] ∼ −3.0.”
• Detailed Abundances for 28 Metal-poor Stars: Stellar Relics in the Milky Way (2008, unknown): “The diamonds are from François et al. (2007).”
• HIGH-RESOLUTION SPECTROSCOPY OF EXTREMELY METAL-POOR STARS FROM SDSS/SEGUE. I. ATMOSPHERIC PARAMETERS AND CHEMICAL COMPOSITIONS (2012, unknown): “Though many metal-poor stars having high Sr/Ba ratios are known (e.g., Honda et al. 2004; François et al. 2007), this object is unique because of its low metallicity ([Fe/H] = −3.7).”
• The stellar halo of the Galaxy (2008, unknown): “In contrast, the neutron-capture elements behave very differently, showing a large spread at low metallicity (Barklem et al. 2005; François et al. 2007, and references therein).”
• The s-Process in Low Metallicity Stars. II. Interpretation of High-Resolution Spectroscopic Observations with AGB models (2011, unknown): “…004 by Christlieb et al. (2004) ([Eu/Fe] = 1.64), CS 31078– 018 by Lai et al. (2008) ([Eu/Fe] = 1.23), CS 29491–069 ([Eu/Fe] = 1.0) and HE 1219-0312 ([Eu/Fe] = 1.4) by Hayek et al. (2009), CS 22183–031 by Honda et al. (2004) ([Eu/Fe] = 1.2), CS 22953–003 by François et al. (2007) ([Eu/Fe] = 1.05).”
• The s process: Nuclear physics, stellar models, and observations (2010, unknown): “Heavy neutron-capture elements of metal-poor stars in the halo have been recently studied with high resolution spectroscopy (Aoki et al., 2005; Burris et al., 2000; François et al., 2007; Honda et al., 2004; McWilliam et al., 1995; Ryan et al., 1996; Simmerer et al., 2004; Sneden et al., 2008).”