SI abundances of 8 A-B stars

Based on non-local thermodynamic equilibrium (NLTE) line formation for Si I, Si II and Si III and high-resolution observed spectra, we determined the NLTE abundances for a sample of nine unevolved A9-B3 type stars with well-determined atmospheric parameters. For each star, NLTE reduces the line-to-line scatter for Si II substantially compared with the LTE case and leads to consistent mean abundances from lines of different ionization stages.

In the hottest star of our sample, {iota} Her, Si II is subject to overionization that drives emission in the lines arising from the high-excitation doublet levels. Our NLTE calculations reproduced 10 emission lines of Si II observed in {iota} Her. The same overionization effect leads to greatly weakened Si II lines, which are observed in absorption in {iota} Her.