NLTE analysis of spectra i: Departures from LTE for A-type stars

¹ Space Telescope Science Division of ESA, Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
² Kapteyn Institute, PO Box 800, 9700 AV Groningen, The Netherlands

Abstract

A-type stars with their shallow convection zones serve as ideal physics laboratories for stellar atmosphere research. In the absence of large scale mixing, processes such as diffusion, mass loss and accretion leave their characteristic imprint on the chemical composition of the photosphere. This characteristic surface pattern can be studied by means of stellar abundance analysis. However, such patterns can be hidden in the large uncertainties of LTE abundances. Thus, detailed NLTE studies that can push stellar abundance analysis beyond the 0.1 dex uncertainty limit are a pre-requisite for using A star atmospheres as physics laboratories.