12C/13C ratio and CNO abundances in the classical very old metal-poor dwarf HD 140283

TL;DR

This study measures the 12C/13C isotopic ratio and CNO abundances in the ancient metal-poor star HD 140283 using high-resolution spectra, providing insights into early Galactic chemical evolution.

Contribution

First precise measurement of 12C/13C ratio in a very old metal-poor dwarf star, informing models of early Galaxy chemical enrichment.

Findings

12C/13C ratio between 27 and 45.

CNO abundances indicate influence of early super-AGB and massive stars.

Supports models of early Galactic chemical evolution.

Abstract

The isotope abundances provide powerful diagnostics of the chemical enrichment in our Galaxy. The star HD 140283 is one of the best-studied very metal-poor dwarf stars. It is very old, and the chemical abundance in this star is a good witness of the chemical composition of the matter in the early Galaxy. The aim of this work is to measure the precise abundances of carbon, nitrogen, oxygen, and mainly the 12C/13C isotopic ratio in this very old metal-poor star in order to have a good reference for the computations of the chemical evolution of the Galaxy. We used very high spectral resolution data, with extremely high signal-to-noise ratios obtained with the spectrographs ESPaDOnS at the CFHT, ESPRESSO at the VLT, and HARPS at the ESO 3.6m telescope. For the first time, we were able to measure the 12C/13C ratio in a very old metal-poor dwarf that was born at the very beginning of the Galaxy: 27 < 12C/13C < 45. We also obtained a precise determination of the abundance of the CNO elements in this star. These abundances suggest that the effect of super-asymptotic giant branch stars or fast-rotating massive stars was significant in the early Galaxy.