Astrophysical Lasers in Optical Fe II Lines in Gas Condensations near η Carinae

摘要

We report here on the discovery of laser action in the range 0.9–2 μm in several spectral lines of Fe II, which are associated with transitions from "pseudo-metastable" states populated by spontaneous transitions from Ly pumped Fe II levels. The intense Ly radiation is formed in the HII region of gas condensations close to the star Car. The laser transitions form together with spontaneous transitions closed radiative cycles, one of which includes the extremely bright 2507/09 ? lines. This fact, together with an accidental mixing of energy levels, may provide an explanation of the abnormal intensities of these UV non-lasing lines. Using the complicated energy level diagram of Fe II we present those peculiar features, which are essential for the inverted population and laser effect: the pumping, the level mixing, and the "bottle neck" for spontaneous decay. The laser action is a new indicator of non-equilibrium and spatially non-homogeneous physical conditions as well as a high brightness temperature of Lyα in ejecta from eruptive stars. Such conditions are very difficult to probe by existing methods.