13 research outputs found
Astrophysical Lasers Operating in optical Fe II Lines Lines in Stellar Ejecta of Eta Carinae
After the discovery of space masers based on OH radicals (Weaver et al, 1965)
and H2O (Cheung et al, 1969) such microwave lasers have been found to work in
more than 100 molecular species (Elitzur, 1992; Townes, 1997), as well as in
highly excited H atoms (Strelnitski et al,1996). In the IR region (10 microns),
the effect of stimulated emission of radiation in the CO2 molecule has been
discovered in the Martian and Venus' atmospheres (Betz et al, 1976; Mumma et
al, 1981). We report here on the discovery of laser action in the range 0.9-2
micr. in several spectral lines of Fe II, which are associated with transitions
from "pseudo-metastable" states populated by spontaneous transitions from
Ly-alpha pumped Fe II levels. The intense Ly-alpha radiation is formed in the
HII region of gas condensations close to the star Eta Carinae. The laser
transitions form together with spontaneous transitions closed radiative cycles,
one of which includes the extremely bright 2507/09 A lines. Closed radiative
cycles, 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 Ly-alpha in ejecta from
eruptive stars. Such conditions are very difficult to probe by existing
methods, and we propose some future experiments. The fact, that the lasing
near-IR lines appear in the spectrum with about the same inten- sity as
non-lasing lines is discussed and compared with the situation in masers.Comment: 27 pages, 11 figures; to be published in A&A; also available at
http://130.235.102.158/blackhole/astrolaser.pd