Testing common classical LTE and NLTE model atmosphere and line-formation codes for quantitative spectroscopy of early-type stars

TL;DR

This paper compares LTE and NLTE model atmosphere and line-formation codes for early-type stars, assessing their accuracy and providing recommendations for improved stellar parameter and abundance determinations, especially for Gaia data.

Contribution

It systematically evaluates different modeling approaches for early-type stars and offers guidance to enhance their accuracy in spectroscopic analysis.

Findings

LTE models perform well for cooler stars but less so for hotter stars.

NLTE models provide more accurate spectra for O-type stars.

Recommendations improve future stellar parameter and chemical abundance measurements.

Abstract

It is generally accepted that the atmospheres of cool/lukewarm stars of spectral types A and later are described well by LTE model atmospheres, while the O-type stars require a detailed treatment of NLTE effects. Here model atmosphere structures, spectral energy distributions and synthetic spectra computed with ATLAS9/SYNTHE and TLUSTY/SYNSPEC, and results from a hybrid method combining LTE atmospheres and NLTE line-formation with DETAIL/SURFACE are compared. Their ability to reproduce observations for effective temperatures between 15000 and 35000 K are verified. Strengths and weaknesses of the different approaches are identified. Recommendations are made as to how to improve the models in order to derive unbiased stellar parameters and chemical abundances in future applications, with special emphasis on Gaia science.