The pristine nature of SMSS 1605$-$1443 revealed by ESPRESSO

Abstract

SMSS J160540.18$-$144323.1 is the carbon-enhanced metal-poor (CEMP) star with the lowest iron abundance ever measured, [Fe/H]=-6.2, which was first reported with the SkyMapper telescope. The carbon abundance is A(C)~6.1 in the low-C band, as the majority of the stars in this metallicity range. Yet, constraining the isotopic ratio of key species, such as carbon, sheds light on the properties and origin of these elusive stars. We performed high-resolution observations of SMSS1605$-$1443 with the ESPRESSO spectrograph to look for variations in the radial velocity ($v_{rad}$) with time. These data have been combined with older MIKE and UVES archival observations to enlarge the temporal baseline. The ${}^{12}$C/${}^{13}$C isotopic ratio is also studied to explore the possibility of mass transfer from a binary companion. A cross-correlation function against a natural template was applied to detect $v_{rad}$ variability and a spectral synthesis technique was used to derive ${}^{12}$C/${}^{13}$C in the stellar atmosphere. We confirm previous indications of binarity in SMSS1605$-$1443 and measured a lower limit ${}^{12}$C/${}^{13}$C$>60$ at more than a 3$\sigma$ confidence level, proving that this system is chemically unmixed and that no mass transfer from the unseen companion has happened so far. Thus, we confirm the CEMP-no nature of SMSS1605$-$1443 and show that the pristine chemical composition of the cloud from which it formed is currently imprinted in its stellar atmosphere free of contamination.

Published in A&A, 9 pages, 6 figures

References in corpus (25)

• ESPRESSO@VLT -- On-sky performance and first results
• First stars VI - Abundances of C, N, O, Li, and mixing in extremely metal-poor giants. Galactic evolution of the light elements
• An extremely primitive halo star
• Carbon-Enhanced Metal-Poor Star Frequencies in the Galaxy: Corrections for the Effect of Evolutionary Status on Carbon Abundances
• Observational Constraints on First-Star Nucleosynthesis. I. Evidence for Multiple Progenitors of CEMP-no Stars
• Bright Metal-Poor Stars from the Hamburg/ESO Survey. I. Selection and Follow-up Observations from 329 Fields
• TOPoS: II. On the bimodality of carbon abundance in CEMP stars. Implications on the early chemical evolution of galaxies
• Binarity in Carbon-Enhanced Metal-Poor stars
• First stars IX -Mixing in extremely metal-poor giants. Variation of the 12C/13C, [Na/Mg] and [Al/Mg] ratios
• An Elemental Assay of Very, Extremely, and Ultra Metal-Poor Stars
• The $R$-Process Alliance: Fourth Data Release from the Search for $r$-Process-Enhanced Stars in the Galactic Halo
• First stars X. The nature of three unevolved Carbon-Enhanced Metal-Poor stars
• Exploiting the Gaia EDR3 photometry to derive stellar temperatures
• Limits on Pop III star formation with the most iron-poor stars
• The first stars: CEMP--no stars and signatures of spinstars
• Faint Population III supernovae as the origin of the most iron-poor stars
• The lowest detected stellar Fe abundance: The halo star SMSS J160540.18-144323.1
• Lithium abundances in CEMP stars
• Survey of Surveys I: The largest catalogue of radial velocities for the Galaxy
• Back to the Lithium Plateau with J0023+0307 with [Fe/H]<-6
• Stellar winds and metal enrichment from fast-rotating Population III stars
• Espresso observations of HE 0107$-$5240 and other CEMP-no stars with $[Fe/H]\le -4.5$
• Metal-poor Stars Observed with the Automated Planet Finder Telescope. III. CEMP-no Stars are the Descendant of Population III Stars
• Protostellar-disc fragmentation across all metallicities
• 12C/13C ratio and CNO abundances in the classical very old metal-poor dwarf HD 140283

Cited by in corpus (6)

• A needle in a haystack? Catching Pop III stars in the Epoch of Reionization: I. Pop III star forming environments
• Evidence of First Stars-enriched Gas in High-redshift Absorbers
• On the 12C/13C isotopic ratio at the dawn of chemical evolution
• A hide-and-seek game: Looking for Population III stars during the Epoch of Reionization through the HeII$\lambda$1640 line
• Explaining the ${}^{12}\text{C}{/}^{13}\text{C}$ ratio in the Galactic halo: the contribution from shell mergers in primordial massive stars
• Population III star formation in the presence of turbulence, magnetic fields and ionizing radiation feedback