SDSS J102915.14+172927.9: Revisiting the chemical pattern

Abstract

Context: The small- to intermediate-mass ($M<0.8M_{\odot }$), most metal-poor stars that formed in the infancy of the Universe are still shining today in the sky. They are very rare, but their discovery and investigation brings new knowledge on the formation of the first stellar generations. Aims: SDSS J102915.14+172927.9 is one of the most metal-poor star known to date. Since no carbon can be detected in its spectrum, a careful upper limit is important, both to classify this star and to distinguish it from the carbon-enhanced stars that represent the majority at these metallicities. Methods: We undertook a new observational campaign to acquire high-resolution UVES spectra. The new spectra were combined with archival spectra in order to increase the signal-to-noise ratio. From the combined spectrum, we derived abundances for seven elements (Mg, Si, Ca, Ti, Fe, Ni, and a tentative Li) and five significant upper limits (C, Na, Al, Sr, and Ba). Results: The star has a carbon abundance A(C) <4.68 and therefore is not enhanced in carbon, at variance with the majority of the stars at this Fe regime, which typically show A(C)> 6.0. A feature compatible with the Li doublet at 670.7 nm is tentatively detected. Conclusions: The upper limit on carbon implies $Z<1.915\times 10^{-6}$, more than 20 times lower than the most iron-poor star known. Therefore, the gas cloud out of which the star was formed did not cool via atomic lines but probably through dust. Fragmentation of the primordial cloud is another possibility for the formation of a star with a metallicity this low.

References in corpus (24)

• Gaia Data Release 3: Summary of the content and survey properties
• galpy: A Python Library for Galactic Dynamics
• First stars VI - Abundances of C, N, O, Li, and mixing in extremely metal-poor giants. Galactic evolution of the light elements
• The Milky Way's circular velocity curve between 4 and 14 kpc from APOGEE data
• An extremely primitive halo star
• First Stars VIII -- Enrichment of the neutron-capture elements in the early Galaxy
• CH in stellar atmospheres: an extensive linelist
• Probing the Formation of the First Low-Mass Stars with Stellar Archaeology
• The updated BaSTI stellar evolution models and isochrones: II. alpha-enhanced calculations
• TOPoS: II. On the bimodality of carbon abundance in CEMP stars. Implications on the early chemical evolution of galaxies
• Gaia Data Release 3: External calibration of BP/RP low-resolution spectroscopic data
• Four-hundred Very Metal-Poor Stars Studied with LAMOST and Subaru. II. Elemental abundances
• Back to the Lithium Plateau with J0023+0307 with [Fe/H]<-6
• Discovery of a thin lithium plateau among metal-poor red giant branch stars
• Young giants of intermediate mass Evidence of rotation and mixing
• NLTE analysis of the methylidyne radical (CH) molecular lines in metal-poor stellar atmospheres
• The Pristine survey XIV: chemical analysis of two ultra-metal-poor stars
• Raising the observed metallicity floor with a 3D non-LTE analysis of SDSS J102915.14+172927.9
• Probing the early Milky Way with GHOST spectra of an extremely metal-poor star in the Galactic disk
• Espresso observations of HE 0107$-$5240 and other CEMP-no stars with $[Fe/H]\le -4.5$
• High-speed stars. II. An unbound star, young stars, bulge metal-poor stars, and Aurora candidates
• An investigation of the formation and line properties of MgH in 3D hydrodynamical model stellar atmospheres
• High speed stars: III. Detailed abundances and binary nature of the extreme speed star GHS143
• Implications of time-dependent molecular chemistry in metal-poor dwarf stars

Cited by in corpus (4)

• Discovery of an $[Fe/H]\sim -4.8$ Star in $Gaia$ XP Spectra
• Unveiling the nature of HE 0107-5240
• A Sequoia stellar candidate with very high 7Li and 9Be
• Detailed Abundance Determination of Metal-Poor Stars with X-Shooter I. Unusual Chemistry in Halo Stars