Carbon and oxygen in metal-poor halo stars

Abstract

Carbon and oxygen are key tracers of the Galactic chemical evolution; in particular, a reported upturn in [C/O] towards decreasing [O/H] in metal-poor halo stars could be a signature of nucleosynthesis by massive Population III stars. We reanalyse carbon, oxygen, and iron abundances in thirty-nine metal-poor turn-off stars. For the first time, we take into account three-dimensional (3D) hydrodynamic effects together with departures from local thermodynamic equilibrium (LTE) when determining both the stellar parameters and the elemental abundances, by deriving effective temperatures from 3D non-LTE H$\beta$ profiles, surface gravities from Gaia parallaxes, iron abundances from 3D LTE Feii equivalent widths, and carbon and oxygen abundances from 3D non-LTE Ci and Oi equivalent widths. We find that [C/Fe] stays flat with [Fe/H], whereas [O/Fe] increases linearly up to $0.75$ dex with decreasing [Fe/H] down to $-3.0$ dex. As such [C/O] monotonically decreases towards decreasing [O/H], in contrast to previous findings, mainly by virtue of less severe non-LTE effects for Oi at low [Fe/H] with our improved calculations.

5 pages, 2 figures; published in A&A Letters

References in corpus (15)

• A grid of MARCS model atmospheres for late-type stars I. Methods and general properties
• The Dawes Review 2: Nucleosynthesis and stellar yields of low and intermediate-mass single stars
• A strong case for fast stellar rotation at very low metallicities
• Both accurate and precise gf-values for FeII lines
• Non-LTE line formation of Fe in late-type stars - III. 3D non-LTE analysis of metal-poor stars
• Sulphur and zinc abundances in Galactic halo stars revisited
• Carbon and oxygen abundances in stellar populations
• The chemical compositions of the extreme halo stars HE0107-5240 and HE1327-2326 inferred from 3D hydrodynamical model atmospheres
• Faint Population III supernovae as the origin of the most iron-poor stars
• Three Ancient Halo Subgiants: Precise Parallaxes, Compositions, Ages, and Implications for Globular Clusters
• Constraining cosmic scatter in the Galactic halo through a differential analysis of metal-poor stars
• G64-12 and G64-37 are Carbon-Enhanced Metal-Poor Stars
• An in-depth spectroscopic examination of molecular bands from 3D hydrodynamical model atmospheres. II. Carbon-enhanced metal-poor 3D model atmospheres
• Possible signature of hypernova nucleosynthesis in a beryllium rich halo dwarf
• Three-dimensional hydrodynamical CO5BOLD model atmospheres of red giant stars. IV. Oxygen diagnostics in extremely metal-poor red giants with infrared OH lines

Cited by in corpus (26)

• The Physical Conditions of Emission-Line Galaxies at Cosmic Dawn from JWST/NIRSpec Spectroscopy in the SMACS 0723 Early Release Observations
• The GALAH Survey: Chemical tagging and chrono-chemodynamics of accreted halo stars with GALAH+ DR3 and $Gaia$ eDR3
• Influence of sub- and super-solar metallicities on the compositions of solid planetary building blocks
• 3D non-LTE line formation of neutral carbon in the Sun
• The Most Metal-Poor Stars. V. The CEMP-no Stars in 3D and Non-LTE
• On the inconsistency of [C/Fe] abundances and the fractions of carbon-enhanced metal-poor stars among various stellar surveys
• The Pristine Inner Galaxy Survey (PIGS) III: carbon-enhanced metal-poor stars in the bulge
• The Gaia-ESO Survey: Carbon abundance in the Galactic thin and thick disks
• Neutron-capture elements in dwarf galaxies II: Challenges for the s- and i-processes at low metallicity
• Machine learning detects multiplicity of the first stars in stellar archaeology data
• The energy distribution of the first supernovae
• Titans metal-poor reference stars. I. Accurate effective temperatures and surface gravities for dwarfs and subgiants from 3D non-LTE H$\alpha$ profiles and Gaia parallaxes
• Gas-phase Fe/O and Fe/N abundances in Star-Forming Regions. Relations between nucleosynthesis, metallicity and dust
• Gaia-Sausage-Enceladus star formation history as revealed by detailed elemental abundances
• The most metal-rich asymptotic giant branch stars
• The impact of carbon and oxygen abundances on the metal-poor initial mass function
• Orbital and atmospheric parameters of two wide O-type subdwarf binaries: BD$-$11${}^{\mathrm{o}}$162 and Feige 80
• Models for Metal-Poor Stars with Different Initial Abundances of C, N, O, Mg, and Si. II. Application to the Colour-Magnitude Diagrams of the Globular Clusters 47 Tuc, NGC 6362, M5, M3, M55, and M92
• Metallicity dependence of the CO-to-H${}_2$ and the [CI]-to-H${}_2$ conversion factors in galaxies
• Empirical Constraints on Core Collapse Supernova Yields using Very Metal Poor Damped Lyman Alpha Absorbers
• Probing Na in giant exoplanets with ESPRESSO and 3D NLTE stellar spectra
• Implications of time-dependent molecular chemistry in metal-poor dwarf stars
• The metal-poorest tail of the Galactic halo: hypothesis on its origin from precise spectral analysis
• An empirical metallicity tracer in CEMP and C-normal stars
• Disentangling Milky Way halo populations at low metallicities using [Al/Fe]
• A comparative study of O, Ne, Cl, and Ar in Hii regions and PNe of the Galactic disk: Temporal evolution of radial gradients?