Lanthanides and other spectral oddities in a Centauri

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 λ4619 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.

Germanium, Arsenic, and Selenium Abundances in Metal-Poor Stars*

“…Elements in this transition between zinc (Zn, Z = 30) and rubidium (Rb, Z = 37) are rarely studied in late-type stars because their intrinsic abundances are relatively low and their strongest absorption lines lie in the ultraviolet (UV), below the atmospheric cutoff near 3000 Å. Some of these intermediate elements have been detected in the atmospheres of so-called chemically-peculiar stars (e.g., Bidelman & Corliss 1962;Leckrone et al 1999;Castelli & Hubrig 2004;Cowley et al 2010). These atmospheres are affected by strong magnetic fields or are stable against convection, allowing radiatively driven diffusion or gravitational settling to chemically stratify the atmosphere.…”