Spectroscopic study of the late B-type eclipsing binary system AR Aurigae A and B: Towards clarifying the differences in atmospheric parameters and chemical abundances

TL;DR

This spectroscopic study of the binary system AR Aurigae A and B reveals detailed atmospheric parameters and elemental abundances, highlighting differences in chemical peculiarities and their relation to stellar composition and evolution.

Contribution

The paper provides the first detailed spectroscopic analysis of both components of AR Aurigae, including non-LTE abundance determinations for 28 elements, clarifying atmospheric and chemical differences.

Findings

AR Aur A shows large chemical peculiarities characteristic of HgMn stars.

AR Aur B exhibits a nearly linear Z-dependence of element abundances with minimal dispersion.

Differences in chemical patterns may explain the emergence of chemical anomalies in similar stars.

Abstract

AR Aur A+B is a close binary of astrophysical interest, because dissimilar surface compositions are reported between similar late B-type dwarfs. A new spectroscopic study on this system was carried out based on the disentangled spectra, in order to determine their atmospheric parameters and elemental abundances, The effective temperature and microturbulence (determined from the equivalent widths of Fe II lines) turned out (11150K, 0.9km/s) and (10650K, 0.1km/s) for A and B. The chemical abundances of 28 elements were derived while taking into account the non-LTE effect for Z<=15 elements (Z: atomic number). The following trends were elucidated for [X/H] (abundance of X relative to the Sun): (1) Qualitatively, [X/H] shows a rough global tendency of increasing with Z, with the gradient steeper for A than for B. (2) However, considerable dispersion is involved for A, since prominently large peculiarities are seen in specific elements reflecting the characteristics of HgMn stars (e.g., very deficient N, Al, Sc, Ni; markedly overabundant P, Mn). (3) In contrast, the Z-dependence of [X/H] for B tends to be nearly linear with only a small dispersion. These observational facts may serve as a key to understanding the critical condition for the emergence of chemical anomaly.