Rare-earth elements in the atmosphere of the magnetic chemically peculiar star HD 144897. New classification of the Nd III spectrum

TL;DR

This study analyzes the magnetic Ap star HD 144897, revealing extreme rare-earth element overabundances, refining Nd III spectral classification, and modeling element stratification to better understand stellar atmospheres.

Contribution

It provides the first detailed REE abundance measurements from multiple ion lines and revises the Nd III spectral classification, enhancing atomic data accuracy.

Findings

REEs are overabundant by about four dex compared to solar levels.

Stratification models successfully fit spectral lines of seven elements.

Revised Nd III energy levels and line classifications significantly improve atomic data.

Abstract

We have obtained a UVES spectrum of a slowly rotating strongly magnetic Ap star, HD 144897, that exhibits very large overabundances of rare-earth elements. Here we present a detailed spectral analysis of this object, also taking into account effects of non-uniform vertical distribution (stratification) of chemical elements. We have determined the photospheric abundances of 40 ions. For seven elements (Mg, Si, Ca, Ti, Cr, Mn, Fe), we have obtained a stratification model that allow us to produce a satisfactory fit to the observed profiles of spectral lines of various strength. REEs abundances, that for the first time in the literature have been determined from the lines of the first and second ions, have been found typically four dex larger than solar abundances. Our analysis of REE spectral lines provide a strong support to the laboratory line classification and determination of the atomic parameters. The only remarkable exception is Nd III, for which spectral synthesis was found to be inconsistent with the observations. We have therefore performed a revision of the Nd III classification. We have confirmed the energies for 11 out of 24 odd energy levels classified previously, and we have derived the energies for additional 24 levels of Nd III, thereby increasing substantially the number of classified Nd III lines with corrected wavelengths and atomic parameters.