Carbon and Oxygen abundances across the Hertzsprung gap

TL;DR

This study analyzes carbon and oxygen abundances in 188 stars across the Hertzsprung gap to understand chemical peculiarities and stellar evolution effects, finding mostly consistent abundances with some peculiarities in Am/Ap stars.

Contribution

It provides a comprehensive spectroscopic analysis of C and O in stars in the Hertzsprung gap, including a large sample with high-resolution spectra, revealing chemical patterns and peculiarities.

Findings

Most stars have C and O abundances similar to lower mass dwarfs.

Am/Ap stars show expected chemical peculiarities.

No evidence of abundance alteration due to evolution across the Hertzsprung gap.

Abstract

We derived atmospheric parameters and spectroscopic abundances for C and O for a large sample of stars located in the Hertzsprung gap in the Hertzsprung-Russell Diagram in order to detect chemical peculiarities and get a comprehensive overview of the population of stars in this evolutionary state. We have observed and analyzed high resolution spectra (R = 60 000) of 188 stars in the mass range 2 - 5 Msun with the 2.7 m Harlan J. Smith Telescope at the McDonald Observatory including 28 stars previously identified as Am/Ap stars. We find that the C and O abundances of the majority of stars in the Hertzsprung gap are in accordance with abundances derived for local lower mass dwarfs but detect expected peculiarities for the Am/Ap stars. The C and O abundances of stars with Teff < 6500 K are slightly lower than for the hotter objects but the C/O ratio is constant in the analyzed temperature domain. No indication of an alteration of the C and O abundances of the stars by mixing during the evolution across the Hertzsprung gap could be found before the homogenization of their atmospheres by the first dredge-up.