Ultraviolet Doubly Excited Fe II Lines in the Laboratory and in the A-Type Star 21 Pegasi

Abstract

During a new investigation of the UV hollow-cathode spectrum of iron, some 120 lines were identified, among them strong lines around 1850 A, as transitions from doubly excited levels in Fe II. A combination of selective population by charge-transfer processes in the laboratory source and of a strong configuration interaction is probably the cause of unexpectedly large intensities of a great number of lines. The new energy levels and calculated oscillator strengths for the newly identified transitions are presented. Most of the new lines coincide with absorption lines in the high-resolution IUE spectrum of the sharp-lined A star 21 Pegasi. For about one-third of them, located mostly in the region 1750-1900 A, the identifications are confirmed by modal atmosphere calculations. For the remaining coincidences the stellar line is probably blended with another contributor.