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Astrophysical lasers operating in optical Fe II lines in stellar ejecta of η Carinae

Johansson, Sveneric LU and Letokhov, Vladilen LU (2004) In Astronomy & Astrophysics 428. p.497-509
Abstract
After the discovery of space masers based on OH radicals (Weaver et al.cite{Wea65}) and H<SUB>2</SUB>O (Cheung et al. cite{Che69}) such microwavelasers have been found to work in more than 100 molecular species(Elitzur cite{Eli92}; Townes cite{Tow97}), as well as in highlyexcited H atoms (Strelnitski et al. cite{Str96}). In the IR region (10mum), the effect of stimulated emission of radiation in the CO<SUB>2</SUB>molecule has been discovered in the Martian and Venus' atmospheres (Betzet al. cite{Bet76}; Mumma et al. cite{Mum81}). We report here on thediscovery of laser action in the range 0.9-2 μm in several spectrallines of Fe II, which are associated with transitions from``pseudo-metastable'' states populated by... (More)
After the discovery of space masers based on OH radicals (Weaver et al.cite{Wea65}) and H<SUB>2</SUB>O (Cheung et al. cite{Che69}) such microwavelasers have been found to work in more than 100 molecular species(Elitzur cite{Eli92}; Townes cite{Tow97}), as well as in highlyexcited H atoms (Strelnitski et al. cite{Str96}). In the IR region (10mum), the effect of stimulated emission of radiation in the CO<SUB>2</SUB>molecule has been discovered in the Martian and Venus' atmospheres (Betzet al. cite{Bet76}; Mumma et al. cite{Mum81}). We report here on thediscovery of laser action in the range 0.9-2 μm in several spectrallines of Fe II, which are associated with transitions from``pseudo-metastable'' states populated by spontaneous transitions fromLyα pumped Fe II levels. The intense Lyα radiation is formedin the HII region of gas condensations close to the star η Car. Thelaser transitions form together with spontaneous transitions closedradiative cycles, one of which includes the extremely bright 2507/09Å lines. Closed radiative cycles, together with an accidentalmixing of energy levels, may provide an explanation of the abnormalintensities of these UV non-lasing lines. Using the complicated energylevel diagram of Fe II we present those peculiar features, which areessential for the inverted population and laser effect: the pumping, thelevel mixing, and the ``bottle neck'' for spontaneous decay. The laseraction is a new indicator of non-equilibrium and spatiallynon-homogeneous physical conditions as well as a high brightnesstemperature of Lyα in ejecta from eruptive stars. Such conditionsare very difficult to probe by existing methods, and we propose somefuture experiments. The fact, that the lasing near-IR lines appear inthe spectrum with about the same intensity as non-lasing lines isdiscussed and compared with the situation in masers. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
atomic processes, line: formation, radiation mechanisms: non-thermal, stars: individual: η Carinae
in
Astronomy & Astrophysics
volume
428
pages
497 - 509
publisher
EDP Sciences
external identifiers
  • wos:000225335100014
  • scopus:10844246213
ISSN
0004-6361
DOI
10.1051/0004-6361:20040379
language
English
LU publication?
yes
id
2fe01eb4-e299-4b05-b7a5-477cb2b6daf2 (old id 134074)
date added to LUP
2007-07-13 12:12:45
date last changed
2017-07-23 04:47:55
@article{2fe01eb4-e299-4b05-b7a5-477cb2b6daf2,
  abstract     = {After the discovery of space masers based on OH radicals (Weaver et al.cite{Wea65}) and H&lt;SUB&gt;2&lt;/SUB&gt;O (Cheung et al. cite{Che69}) such microwavelasers have been found to work in more than 100 molecular species(Elitzur cite{Eli92}; Townes cite{Tow97}), as well as in highlyexcited H atoms (Strelnitski et al. cite{Str96}). In the IR region (10mum), the effect of stimulated emission of radiation in the CO&lt;SUB&gt;2&lt;/SUB&gt;molecule has been discovered in the Martian and Venus' atmospheres (Betzet al. cite{Bet76}; Mumma et al. cite{Mum81}). We report here on thediscovery of laser action in the range 0.9-2 μm in several spectrallines of Fe II, which are associated with transitions from``pseudo-metastable'' states populated by spontaneous transitions fromLyα pumped Fe II levels. The intense Lyα radiation is formedin the HII region of gas condensations close to the star η Car. Thelaser transitions form together with spontaneous transitions closedradiative cycles, one of which includes the extremely bright 2507/09Å lines. Closed radiative cycles, together with an accidentalmixing of energy levels, may provide an explanation of the abnormalintensities of these UV non-lasing lines. Using the complicated energylevel diagram of Fe II we present those peculiar features, which areessential for the inverted population and laser effect: the pumping, thelevel mixing, and the ``bottle neck'' for spontaneous decay. The laseraction is a new indicator of non-equilibrium and spatiallynon-homogeneous physical conditions as well as a high brightnesstemperature of Lyα in ejecta from eruptive stars. Such conditionsare very difficult to probe by existing methods, and we propose somefuture experiments. The fact, that the lasing near-IR lines appear inthe spectrum with about the same intensity as non-lasing lines isdiscussed and compared with the situation in masers.},
  author       = {Johansson, Sveneric and Letokhov, Vladilen},
  issn         = {0004-6361},
  keyword      = {atomic processes,line: formation,radiation mechanisms: non-thermal,stars: individual: η Carinae},
  language     = {eng},
  pages        = {497--509},
  publisher    = {EDP Sciences},
  series       = {Astronomy & Astrophysics},
  title        = {Astrophysical lasers operating in optical Fe II lines in stellar ejecta of η Carinae},
  url          = {http://dx.doi.org/10.1051/0004-6361:20040379},
  volume       = {428},
  year         = {2004},
}