An extremely primitive halo star

Abstract

The early Universe had a chemical composition consisting of hydrogen, helium and traces of lithium1, almost all other elements were created in stars and supernovae. The mass fraction, Z, of elements more massive than helium, is called "metallicity". A number of very metal poor stars have been found some of which, while having a low iron abundance, are rich in carbon, nitrogen and oxygen. For theoretical reasons and because of an observed absence of stars with metallicities lower than Z=1.5E-5, it has been suggested that low mass stars (M<0.8M\odot, the ones that survive to the present day) cannot form until the interstellar medium has been enriched above a critical value, estimated to lie in the range 1.5E-8\leqZ\leq1.5E-6, although competing theories claiming the contrary do exist. Here we report the chemical composition of a star with a very low Z\leq6.9E-7 (4.5E-5 of that of the Sun) and a chemical pattern typical of classical extremely metal poor stars, meaning without the enrichment of carbon, nitrogen and oxygen. This shows that low mass stars can be formed at very low metallicity. Lithium is not detected, suggesting a low metallicity extension of the previously observed trend in lithium depletion. Lithium depletion implies that the stellar material must have experienced temperatures above two million K in its history, which points to rather particular formation condition or internal mixing process, for low Z stars.

Published on Nature, 2011 Volume 477, Issue 7362, pp. 67-69

References in corpus (10)

• Primordial Nucleosynthesis: from precision cosmology to fundamental physics
• First Stars VIII -- Enrichment of the neutron-capture elements in the early Galaxy
• HE 0557-4840 - Ultra-Metal-Poor and Carbon-Rich
• First stars VII. Lithium in extremely metal poor dwarfs
• Probing the Formation of the First Low-Mass Stars with Stellar Archaeology
• HE 1327-2326, an unevolved star with [Fe/H]<-5.0. II. New 3D-1D corrected abundances from a VLT/UVES spectrum
• First Stars XI. Chemical composition of the extremely metal-poor dwarfs in the binary CS 22876--032
• Extremely metal-poor stars from the SDSS
• Beryllium in Ultra-Lithium-Deficient Halo Stars - The Blue Straggler Connection
• The CIFIST 3D model atmosphere grid

Cited by in corpus (32)

• The GALAH Survey: Scientific Motivation
• Carbon-Enhanced Metal-Poor Star Frequencies in the Galaxy: Corrections for the Effect of Evolutionary Status on Carbon Abundances
• Primordial Star Formation under the Influence of Far Ultraviolet Radiation: 1540 Cosmological Halos and the Stellar Mass Distribution
• The First Billion Years Project: The escape fraction of ionizing photons in the epoch of reionization
• Binarity in Carbon-Enhanced Metal-Poor stars
• The Birth of a Galaxy. II. The Role of Radiation Pressure
• High-Resolution Spectroscopic Study of Extremely Metal-Poor Star Candidates from the SkyMapper Survey
• The Best and Brightest Metal-Poor Stars
• Constraining the primordial initial mass function with stellar archaeology
• Exploring the Origin of Lithium, Carbon, Strontium and Barium with four new Ultra Metal-Poor Stars
• Decoding the stellar fossils of the dusty Milky Way progenitors
• Extremely metal-poor gas at a redshift of 7
• Carbon-Enhanced Metal-Poor Stars: Relics from the Dark Ages
• Elemental abundances and classification of CEMP stars
• Recovery from population III supernova explosions and the onset of second generation star formation
• Faint Population III supernovae as the origin of the most iron-poor stars
• Large-Scale Structure Formation: from the first non-linear objects to massive galaxy clusters
• Supersonic Relative Velocity between Dark Matter and Baryons: A Review
• Supernova dust formation and the grain growth in the early universe: The critical metallicity for low-mass star formation
• The origin of the most iron-poor star
• Low-mass star formation triggered by early supernova explosions
• The origin of low [alpha/Fe] ratios in extremely metal-poor stars
• An equatorial ultra iron-poor star identified in BOSS
• Low-metallicity star formation: Relative impact of metals and magnetic fields
• The low Sr/Ba ratio on some extremely metal-poor stars
• Constraining Big Bang lithium production with recent solar neutrino data
• A particle dark matter footprint on the first generation of stars
• Growth of dust grains in a low-metallicity gas and its effect on the cloud fragmentation
• The Panchromatic High-Resolution Spectroscopic Survey of Local Group Star Clusters - I. General Data Reduction Procedures for the VLT/X-shooter UVB and VIS arm
• Evolution of the First Supernovae in Protogalaxies: Dynamics of Mixing of Heavy Elements
• What have we learned from observational cosmology ?
• Science Case and Requirements for the MOSAIC Concept for a Multi-Object Spectrograph for the European Extremely Large Telescope