Raising the observed metallicity floor with a 3D non-LTE analysis of SDSS J102915.14+172927.9

Abstract

Context: The first stars produced the first heavy elements and set the stage for the formation of the first galaxies. Accurate chemical abundances of ultra metal-poor stars ([Fe/H]<-4) can be used to infer properties of the first stars, and thus the formation mechanism for low-mass second generation stars in the early universe. Spectroscopic studies have shown that most second generation stars are carbon-enhanced with one notable exception SDSS J102915.14+172927.9. Aims: We reanalyse the composition of SDSS J102915.14+172927.9. Methods: We developed a tailored 3D model atmosphere for SDSS J102915.14+172927.9 with the Stagger-code, making use of an improved surface gravity estimate based on the Gaia DR3 parallax. This model was used as input in the radiative transfer code Balder to compute 3D non-LTE synthetic spectra. These spectra were then used to infer abundances for Mg, Si, Ca, Fe and Ni, and upper limits on Li, Na and Al. 3D LTE synthetic spectra were computed with Scate to infer the abundance of Ti and upper limits on C and N. Results: In contrast to earlier works based on 1D non-LTE corrections to 3D LTE results, we are able to achieve ionisation balance for Ca I and Ca II when employing our consistent 3D non-LTE treatment. Moreover, the elemental abundances are systematically higher than those found in earlier works. In particular, [Fe/H] increases by 0.57 dex, and the upper limits of C and N increase by 0.90 dex and 1.82 dex, respectively. Conclusions: We find that Population III progenitors with masses 10-20 M_sun exploding with energy E<=3*10^{51} erg can reproduce our 3D non-LTE abundance pattern. Contrary to previous work, we obtain higher upper limits on the carbon abundance that are ``marginally consistent'' with star formation through atomic line cooling, and as such, prevent strong conclusions about the formation mechanism of this low mass star.

14 pages, 9 figures, Accepted for publication in Astronomy & Astrophysics

References in corpus (24)

• A grid of MARCS model atmospheres for late-type stars I. Methods and general properties
• The chemical make-up of the Sun: A 2020 vision
• Carbon Enhanced Metal-Poor Stars. I. Chemical Compositions of 26 Stars
• An extremely primitive halo star
• Carbon-Enhanced Metal-Poor Star Frequencies in the Galaxy: Corrections for the Effect of Evolutionary Status on Carbon Abundances
• The Mass Spectrum of the First Stars
• Probing the Formation of the First Low-Mass Stars with Stellar Archaeology
• Hydrodynamics of core-collapse supernovae and their progenitors
• The stellar content of the Hamburg/ESO survey. IV. Selection of candidate metal-poor stars
• Non-LTE line formation of Fe in late-type stars - III. 3D non-LTE analysis of metal-poor stars
• Non-LTE aluminium abundances in late-type stars
• Constraining the primordial initial mass function with stellar archaeology
• The solar silicon abundance based on 3D non-LTE calculations
• 3D NLTE spectral line formation of lithium in late-type stars
• Nucleosynthesis in a Primordial Supernova: Carbon and Oxygen Abundances in SMSS J031300.36-670839.31
• 3D NLTE analysis of the most iron-deficient star, SMSS0313-6708
• Faint Population III supernovae as the origin of the most iron-poor stars
• The formation of the Milky Way halo and its dwarf satellites; a NLTE-1D abundance analysis. II. Early chemical enrichment
• Evidence for an aspherical Population III supernova explosion inferred from the hyper metal-poor star HE1327-2326
• 3D non-LTE iron abundances in FG-type dwarfs
• A Minimum Dilution Scenario for Supernovae and Consequences for Extremely Metal-Poor Stars
• Observational constraints on the survival of pristine stars
• Extremely metal-poor stars from the SDSS
• Titanium abundances in late-type stars I. 1D non-local thermodynamic equilibrium modelling in benchmark dwarfs and giants

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