Carbon and oxygen abundances in stellar populations

TL;DR

This study measures carbon, oxygen, and iron abundances in nearby stars to understand their origins and differences among stellar populations, revealing trends related to galaxy evolution and planet formation.

Contribution

It provides new detailed abundance measurements for different stellar populations using non-LTE corrections and MARCS models, highlighting systematic differences and potential links to planet hosting.

Findings

High- and low-alpha halo stars show different [C/Fe] and [O/Fe] trends.

Thin-disk stars have higher [C/O] ratios than thick-disk stars.

C/O ratios in stars do not exceed 0.8, impacting planet formation theories.

Abstract

Abundances of C, O, and Fe are determined for F and G main-sequence stars in the solar neighborhood in order to study trends and systematic differences in the C/Fe, O/Fe, and C/O ratios for stellar populations. Carbon abundances are determined from the CI lines at 5052 and 5380 AA and oxygen abundances from the OI triplet at 7774 AA and the [OI] line at 6300 AA. MARCS model atmospheres are applied and non-LTE corrections for the OI triplet are included. Systematic differences between high- and low-alpha halo stars and between thin- and thick-disk stars are seen in the trends of [C/Fe] and [O/Fe]. The two halo populations and thick-disk stars show the same trend of [C/O] versus [O/H], whereas thin-disk stars are shifted to higher [C/O]. Furthermore, we find some evidence of higher C/O and C/Fe ratios in stars hosting planets than in stars for which no planets have been detected. The results suggest that C and O in both high- and low-alpha halo stars and in thick-disk stars are made mainly in massive stars, whereas thin-disk stars have an additional carbon contribution from low-mass AGB and massive stars of high metallicity causing a rising trend of C/O with increasing metallicity. However, the C/O ratio does not exceed 0.8, which seems to exclude formation of carbon planets if proto-planetary disks have the same composition as their parent stars.