Photospheric carbon, nitrogen, and oxygen abundances of A-type main-sequence stars

TL;DR

This study measures the abundances of carbon, nitrogen, and oxygen in 100 A-type main-sequence stars, revealing general underabundance patterns and correlations with stellar parameters, and compares findings with theoretical models of atomic diffusion.

Contribution

It provides a comprehensive analysis of CNO abundances in A-type stars, including both normal and chemically peculiar stars, and explores their relation to stellar parameters and theoretical predictions.

Findings

CNO are generally underabundant relative to Procyon.

Peculiar stars show larger underabundances, especially in late Am and HgMn stars.

Abundance variations correlate with rotational velocity and are consistent with atomic diffusion models.

Abstract

Based on the spectrum fitting method applied to CI 5380, NI 7486, and OI 6156-8 lines, we determined the abundances of C, N, and O for 100 mostly A-type main-sequence stars (late B through early F at 11000K>Teff>7000K) comprising normal stars as well as non-magnetic chemically peculiar (CP) stars in the projected rotational velocity range of 0km/s<vsini<100km/s, where our aim was to investigate the abundance anomalies of these elements in terms of mutual correlation, dependence upon stellar parameters, and difference between normal and CP stars. We found that CNO are generally underabundant (relative to the standard star Procyon) typically by several tenths dex to ~1dex for almost all stars (regardless of CP or normal), though those classified as peculiar (Am or HgMn) tend to show larger underabundance, especially for C in late Am stars and for N in HgMn stars of late B-type, for which deficiency amounts even up to ~2dex. While the behaviors of these three elements are qualitatively similar to each other, the quantitative extent of peculiarity (or the vulnerability to the physical process causing anomaly) tends to follow the inequality relation of C>N>O. Regarding the considerable star-to-star dispersion observed at any Teff, the most important cause is presumably the difference in rotational velocity. These observational facts appear to be more or less favorably compared with the recent theoretical calculations based on the model of atomic diffusion and envelope mixing.