Slowly Rotating Peculiar Star BD+00$^\circ$1659 as a Benchmark for Stratification Studies in Ap/Bp Stars

TL;DR

This study analyzes the magnetic silicon star BD+00$^\u00b0$1659 to understand vertical element distribution, demonstrating stratification effects and providing a benchmark for similar Ap/Bp star investigations.

Contribution

It offers a self-consistent stratification analysis of BD+00$^\u00b0$1659, highlighting abundance jumps and ionization imbalances as evidence of atmospheric stratification in peculiar stars.

Findings

Iron and silicon show a 1.5 dex abundance jump at specific atmospheric depths.

Non-LTE effects on iron are minor in the stratified atmosphere.

Results aid understanding of stratification impacts on flux in similar rapidly rotating stars.

Abstract

We present the results of a self-consistent analysis of the magnetic silicon star BD+00$^\circ$1659, based on its high-resolution spectra taken from the ESPaDOnS archive (R = 68,000). This narrow-lined star shows the typical high Si abundance and Si II-III anomaly, making it an ideal prototype for investigating the vertical distribution of Si and Fe in the stellar atmosphere. The derived abundances, ranging from helium to lanthanides, confirm the star's classification as a silicon Bp spectral type. Silicon and iron are represented by lines of different ionisation stages (Fe I-III, Si I-III), indicating an ionisation imbalance interpreted as evidence of atmospheric stratification. Our stratification analysis reveals that there is a jump in iron and silicon abundances of 1.5 dex at atmospheric layers with an optical depth of $log\tau_{5000}$ = $-$0.85-$-$1.00. Non-LTE calculations for iron in this stratified atmosphere show minor non-LTE effects. Our results can be applied to studying the impact of stratification on the emergent flux in rapidly rotating Si stars with similar atmospheric parameters and abundance anomalies (for example, MX TrA), where direct stratification analysis is challenging due to line~blending.