Chemical diversity among A-B stars with low rotational velocities: non-LTE abundance analysis

TL;DR

This study analyzes the chemical element abundances in nine low-rotation A-B stars using advanced non-LTE models, revealing correlations between temperature and element enhancement, and providing new insights into stellar and galactic chemical compositions.

Contribution

It introduces new non-LTE abundance analyses for 14 elements in A-B stars, including updated atomic models for Zr, Sr, and Ba, and compares stellar compositions with solar and galactic standards.

Findings

Stars with T_eff < 10500 K show supersolar heavy element abundances.

Enhancement of Ba exceeds that of other heavy elements in these stars.

HD 73666 shows no deviation from Praesepe cluster composition.

Abstract

We present accurate element abundance patterns based on the non-local thermodynamic equilibrium (non-LTE, NLTE) line formation for 14 chemical elements from He to Nd for a sample of nine A9 to B3 type stars with well determined atmospheric parameters and low rotational velocities. We constructed new model atom of Zr II-III and updated model atoms for Sr II and Ba II by implementing the photoionization cross sections from calculations with the Dirac B-spline R-matrix method. The NLTE abundances of He to Fe in the stars HD~17081, HD~32115, HD~160762, and HD~209459 are found to be consistent with the solar abundances, and HD~73666 being a Blue Struggler does not reveal deviations from chemical composition of the Praesepe cluster. Three of these stars with an effective temperature of lower than 10500~K have supersolar abundances of Sr, Zr, Ba, and Nd, and our results suggest the presence of a positive correlation between stellar effective temperature and abundance. For each star, enhancement of Ba is higher than that for any other heavy element. We propose that the solar Ba abundance is not representative of the galactic Ba abundance at modern epoch. The status of HD~145788 was not clarified: this star has solar abundances of C to Si and enhancements of Sr to Ba similar to that for superficially normal stars of similar temperature, while overabundant Ca, Ti, and Fe. The NLTE abundances of Vega support its status of a mild lambda~Bootis star.