On the ultraviolet iron spectrum of pre-white dwarfs.

Abstract

The authors have detected numerous lines of Fe V, Fe VI, and Fe VII in high-resolution IUE spectra of two central stars and a number of very hot subdwarfs. The strengths of these lines vary widely from star to star, suggesting that the abundance of iron in the atmospheres of the immediate progenitors of white dwarfs in strongly variable. A possible explanation is elemental separation by gravity and radiation pressure.