Model atmospheres of chemically peculiar stars: Self-consistent empirical stratified model of HD24712

TL;DR

This paper presents the first empirical, self-consistent atmospheric model of the chemically peculiar star HD24712, incorporating chemical stratification derived directly from spectral line profiles, revealing significant structural changes and temperature gradients.

Contribution

The study introduces a novel empirical method to model chemically peculiar star atmospheres with stratified elements, improving the consistency between observed spectra and atmospheric structure.

Findings

Stratification causes significant changes in atmospheric structure.

An inverse temperature gradient exists in the upper atmosphere.

Maximum temperature increase of about 600K due to element accumulation.

Abstract

High-resolution spectra of some chemically peculiar stars clearly demonstrate the presence of strong abundance gradients in their atmospheres. However, these inhomogeneities are usually ignored in the standard scheme of model atmosphere calculations, braking the consistency between model structure and spectroscopically derived abundance pattern. In this paper we present first empirical self-consistent stellar atmosphere model of roAp star HD24712, with stratification of chemical elements included, and which is derived directly from the observed profiles of spectral lines without time-consuming simulations of physical mechanisms responsible for these anomalies. We used the LLmodels stellar model atmosphere code and DDAFIT minimization tool for analysis of chemical elements stratification and construction of self-consistent atmospheric model. Empirical determination of Pr and Nd stratification in the atmosphere of HD24712 is based on NLTE line formation for Prii/iii and Ndii/iii with the use of the DETAIL code. Based on iterative procedure of stratification analysis and subsequent re-calculation of model atmosphere structure we constructed a self-consistent model of HD24712, i.e. the model which temperature-pressure structure is consistent with results of stratification analysis. It is shown that stratification of chemical elements leads to the considerable changes in model structure as to compare with non-stratified homogeneous case. We find that accumulation of REE elements allows for the inverse temperature gradient to be present in upper atmosphere of the star with the maximum temperature increase of about 600K.