Lanthanides and other spectral oddities in a Centauri

TL;DR

This study identifies lanthanides such as Ce III and Kr II in the spectrum of the peculiar star a Cen, revealing its role as a transitional object between different types of chemically peculiar stars.

Contribution

The paper provides the first robust identification of Ce III and Kr II in a Cen, and discusses the implications for stellar classification and spectral features.

Findings

Robust identification of Ce III and Kr II in a Cen

Nd III likely present in the spectrum

Broad absorption features are not fully explained

Abstract

Context: There is considerable interest in the helium variable a Cen as a bridge between helium-weak and helium-strong CP stars. Aims: We investigate Ce III and other possible lanthanides in the spectrum the of hottest chemically peculiar (CP) star in which these elements have been found. A {Kr II line appears within a broad absorption which we suggest may be due to a high-level transition in C II. Methods: Wavelengths and equivalent widths are measured on high-resolution UVES spectra, analyzed, and their phase-variations investigated. Results: New, robust identifications of Ce III and Kr II are demonstrated. Nd III is likely present. A broad absorption near 4619[A] is present at all phases of a Cen, and in some other early B stars. Conclusions: The presence of lanthanides in a Cen strengthens the view that this star is a significant link between the cooler CP stars and the hotter helium-peculiar stars. Broad absorptions in a Cen are not well explained.