Stellar Archaeology: a Keck Pilot Program on Extremely Metal-Poor Stars from the Hamburg/ESO Survey. II. Abundance Analysis

Abstract

We present a detailed abundance analysis of 8 stars selected as extremely metal poor candidates from the Hamburg/ESO Survey (HES). For comparison, we have also analysed 3 extremely metal-poor candidates from the HK survey, and 3 additional bright metal-poor stars. With this work, we have doubled the number of extremely metal-poor stars ([Fe/H]$\le 3.0$) with high-precision abundance analyses. Our sample of extremely metal-poor candidates from the HES contains 3 stars with [Fe/H] $\le -3.0$, 3 more with [Fe/H]$\le -2.8$, and 2 stars that are only slightly more metal rich. Thus, the chain of procedures that led to the selection of these stars from the HES successfully provides a high fraction of extremely metal-poor stars. We verify that our stellar parameters, derived in Paper I, lead to acceptable ionization and excitation balances for Fe, ruling out substantial non-LTE effects in Fe. For the $\alpha -$elements Mg, Si, Ca, Ti, the light element Al, the iron-peak elements Sc, Cr, Mn, and the neutron capture elements Sr and Ba, we find trends in abundance ratios [X/Fe] similar to those found by previous studies. However,the scatter in most of these ratios, even at [Fe/H]$\le -3.0$ dex, is surprisingly small. Only Sr and Ba show scatter larger than the expected errors. Future work (the 0Z project) will provide much stronger constraints on the scatter (or lack thereof) in abundances for a greater number of stars. We discuss the implications of these results for the early chemical evolution of the Galaxy, including such issues as the number of contributing SN, and the sizes of typical fragments in which they were born. In addition, we have identified a very metal poor star that appears to be the result of the s-process chain, operating in a very metal-poor environment, with extremely enhanced C, Ba, and Pb, and somewhat enhanced Sr.

36 pages, 9 tables, 14 figures included; accepted for publication in the July 2002 issue of The Astronomical Journal

References in corpus (1)

• Stellar Archaeology: a Keck Pilot Program on Extremely Metal-Poor Stars From the Hamburg/ESO Survey. I Stellar Parameters

Cited by in corpus (96)

• First stars V - Abundance patterns from C to Zn and supernova yields in the early Galaxy
• A Search for Stars of Very Low Metal Abundance. VI. Detailed Abundances of 313 Metal-Poor Stars
• The Stellar Abundances for Galactic Archeology (SAGA) Database - Compilation of the Characteristics of Known Extremely Metal-Poor Stars
• Detailed Abundances for 28 Metal-poor Stars: Stellar Relics in the Milky Way
• Abundances for metal-poor stars with accurate parallaxes I. Basic data
• The First Cosmic Structures and their Effects
• The Most Metal-Poor Stars. II. Chemical Abundances of 190 Metal-Poor Stars Including 10 New Stars With [Fe/H] < -3.5
• First Stars VIII -- Enrichment of the neutron-capture elements in the early Galaxy
• The evolution of the Milky Way from its earliest phases : constraints on stellar nucleosynthesis
• HE 0557-4840 - Ultra-Metal-Poor and Carbon-Rich
• HE0107-5240, A Chemically Ancient Star.I. A Detailed Abundance Analysis
• Normal and Outlying Populations of the Milky Way Stellar Halo at [Fe/H] < -2
• Spectroscopic Studies of Very Metal-Poor Stars with the Subaru High Dispersion Spectrograph. III. Light Neutron-Capture Elements
• 'Sculptor'-ing the Galaxy? The Chemical Compositions of Red Giants in the Sculptor Dwarf Spheroidal Galaxy
• The stellar content of the Hamburg/ESO survey. IV. Selection of candidate metal-poor stars
• Multi-Element Abundance Measurements from Medium-Resolution Spectra. II. Catalog of Stars in Milky Way Dwarf Satellite Galaxies
• Chemical Evolution in Hierarchical Models Of Cosmic Structure I: Constraints on the Early Stellar Initial Mass Function
• Modelling chemical abundance distributions for dwarf galaxies in the Local Group: the impact of turbulent metal diffusion
• Abundances In Very Metal Poor Dwarf Stars
• Extremely metal-poor stars in classical dwarf spheroidal galaxies: Fornax, Sculptor and Sextans
• JINAbase: A database for chemical abundances of metal-poor stars
• New Extremely Metal-Poor Stars in the Galactic Halo
• VLT/UVES Spectroscopy of Individual Stars in Three Globular Clusters in the Fornax Dwarf Spheroidal Galaxy
• Stellar Archaeology -- Exploring the Universe with Metal-Poor Stars
• Sulphur and zinc abundances in Galactic stars and damped Lyman-alpha systems
• Abundances for metal-poor stars with accurate parallaxes II. alpha-elements in the halo
• The Origin of the Heavy Elements: Recent Progress in the Understanding of the r-Process
• Abundance Analysis of HE2148-1247, A Star With Extremely Enhanced Neutron Capture Elements
• Stellar Archaeology: a Keck Pilot Program on Extremely Metal- Poor Stars From the Hamburg/ESO Survey. III. The Lead (Pb) Star HE 0024-2523
• Abundance Analysis of Turn-Off and Early Subgiant Stars in the Globular Cluster 47 Tuc (NGC 104)
• The Most Metal-Poor Stars. III. The Metallicity Distribution Function and CEMP Fraction
• s-Process in Low Metallicity Stars. III. Individual analysis of CEMP-s and CEMP-s/r with AGB models
• Nucleosynthesis, Reionization, and the Mass Function of the First Stars
• Non-LTE line formation for heavy elements in four very metal-poor stars
• Carbon Stars in the Hamburg/ESO Survey: Abundances
• Abundances in red giant stars of NGC 2808 and correlations between chemical anomalies and global parameters in globular clusters
• Chemical Evolution of the Galactic Bulge as Derived from High-Resolution Infrared Spectroscopy of K and M Red Giants
• First stars IV.CS 29497-030: Evidence for operation of the s-process at very low metallicity
• On the origin of HE0107-5240, the most iron deficient star presently known
• Iron abundances from high-resolution spectroscopy of the open clusters NGC 2506, NGC 6134, and IC 4651
• An inhomogeneous model for the Galactic halo: a possible explanation for the spread observed in s- and r-process elements
• Mg abundances in metal-poor halo stars as a tracer of early Galactic mixing
• A Search for Nitrogen-Enhanced Metal-Poor Stars
• Neutron-Capture Nucleosynthesis in the First Stars
• Principal Component Analysis on Chemical Abundances Spaces
• The Ages and Abundances of a Sample of Globular Clusters in M49 (NGC 4472)
• Chemical abundances in 43 metal-poor stars
• The Stellar Abundances for Galactic Archaeology (SAGA) Database III - Analysis of Enrichment Histories for Elements and Two Modes of Star Formation during the Early Evolution of Milky Way
• From First Stars to the Spite Plateau: a Possible Reconciliation of Halo Stars Observations with Predictions from Big Bang Nucleosynthesis
• Detailed Abundances of Two Very Metal-Poor Stars in Dwarf Galaxies
• Are There Any Stars Lacking Neutron-Capture Elements? Evidence from Strontium and Barium
• Metal-poor stars towards the Galactic bulge - a population potpourri
• Broadband UBVRI Photometry of Horizontal-Branch and Metal-Poor Candidates from the HK and Hamburg/ESO Surveys. I
• Carbon-enhanced metal-poor stars: a window on AGB nucleosynthesis and binary evolution. I. Detailed analysis of 15 binary stars with known orbital periods
• Detection of low Eu abundances in extremely metal-poor stars and the origin of r-process elements
• The effects of thermohaline mixing on low-metallicity asymptotic giant branch stars
• From actinides to zinc: Using the full abundance pattern of the brightest star in Reticulum II to distinguish between different r-process sites
• Oxygen Overabundance in the Extremely Iron-Poor Star CS29498-043
• A New Type of Extremely Metal Poor Star
• Chemical Inhomogeneities in the Milky Way Stellar Halo
• The chemical evolution of a Milky Way-like galaxy: the importance of a cosmologically motivated infall law
• The Spatial Distribution of the Galactic First Stars I: High-Resolution N-body Approach
• Effects of Galactic fountains and delayed mixing in the chemical evolution of the Milky Way
• Binary Blue Metal-Poor Stars: Evidence for AGB Mass Transfer
• Stellar Archaeology: a Keck Pilot Program on Extremely Metal-Poor Stars From the Hamburg/ESO Survey. I Stellar Parameters
• Spectroscopic Studies of Extremely Metal-Poor Stars with Subaru/HDS:I. Observational Data
• Giants reveal what dwarfs conceal: Li abundance in lower RGB stars as diagnostic of the primordial Li
• The Mass Distribution of Population III Stars
• Stochastic chemical enrichment in metal-poor systems II. Abundance ratios and scatter
• The value-added catalogue for LAMOST DR8 low-resolution spectra
• On the early evolution of the Galactic Halo
• Stochastic chemical enrichment in metal-poor systems I. Theory
• Galaxy Genesis -- unravelling the epoch of dissipation in the early disk
• Chemical abundances and kinematics of a sample of metal-rich barium stars
• Chemical analysis of giant stars in the young open cluster NGC 3114
• Detailed Abundances of 15 Stars in the Metal-Poor Globular Cluster NGC 4833
• Chemical Compositions of Kinematically Selected Outer Halo Stars
• The chemical abundance pattern of the extremely metal-poor thin disk star 2MASS J1808-5104 and its origins
• Constraints on Early Nucleosynthesis from the Abundance Pattern of a Damped Ly-alpha System at z = 2.626
• Abundances of Extremely Metal-Poor Star Candidates
• CD-62\degree1346: an extreme halo or hypervelocity CH~star?
• Oxygen and Magnesium Abundance in the Ultra-Metal-Poor Giants CS22949-037 and CS29498-043: Challenges in Models of Atmospheres
• Consistent Iron Abundances Derived from Neutral and Singly-Ionized Iron Lines in Ultraviolet and Optical Spectra of Six Warm Metal-Poor Stars
• Clues to the nature of damped Lyman alpha systems from chemical evolution models
• The Origin of the Heaviest Metals in Most Ultra-Faint Dwarf Galaxies
• Enrichment of Strontium in Dwarf Galaxies
• Fates of the oldest intermediate-mass stars - Primordial to Extremely Metal-Poor AGB and Super-AGB Stars: White Dwarf or Supernova progenitors
• The metal-poor end of the Spite plateau. II. Detailed chemical investigation
• Chemical composition of two bright extremely metal-poor stars from the SDSS MARVELS pre-survey
• Manganese evolution in Omega Centauri: a clue to the cluster formation mechanisms?
• The Binary Dwarf Carbon Star SDSS J125017.90+252427.6
• Observations of Neutron-Capture Elements in the Early Galaxy
• The s-process enriched star HD 55496: origin from a globular cluster or from the tidal disruption of a dwarf galaxy?
• The early phases of Milky Way's chemical evolution
• Europium enrichment and hierarchical formation of the Galactic halo
• First Star Survivors as Metal-Rich Halo Stars that Experienced Supernova Explosions in Binary Systems