| 1. |
- Hartman, Henrik, et al.
(författare)
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Time variations of the narrow Fe II and H I spectral emission lines from the close vicinity of Eta Carinae during the spectral event of 2003
- 2005
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Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 436:3, s. 945-952
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Tidskriftsartikel (refereegranskat)abstract
- The spectrum of Eta Carinae and its ejecta shows slow variations over a period of 5.5 years. However, the spectrum changes drastically on a time scale of days once every period called the "spectral event". We report on variations in the narrow emission line spectrum of gas condensations (the Weigelt blobs) close to the central star during a spectral event. The rapid changes in the stellar radiation field illuminating the blobs make the blobs a natural astrophysical laboratory to study atomic photoprocesses. The different responses of the HI Paschen lines, fluorescent < Fe II > lines and forbidden [Fe II] lines allow us to identify the processes and estimate physical conditions in the blobs. This paper is based on observations from the Pico dos Dias Observatory (LNA/Brazil) during the previous event in June 2003.
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| 2. |
- Johansson, Sveneric, et al.
(författare)
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A model for the origin of the anomalous and very bright UV lines of Fe II in gaseous condensations of the star eta Carinae
- 2001
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Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 378, s. 266-278
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Tidskriftsartikel (refereegranskat)abstract
- We present a qualitative physical model of the origin of two very brightUV lines of Fe II at 2507-2509 Å, present in high-resolutionspectra of gaseous condensations (blobs) close to the central star ofeta Carinae. The spectra have been obtained with the Hubble SpaceTelescope (HST). The model is based on a type of Bowen mechanism withselective photoexcitation of Fe II by a broad HLyalpha profile,generated in the HII region and diffusely transferred to the opticallythick HI region. The frequency distribution by large Doppler diffusioninto the HI region provides a substantial broadening of HLyalpha , whichmakes it possible to selectively photo-excite short-lived (~1 ns) statesat 11.2 eV in Fe II. Within the frame of the present model the intenseHLyalpha radiation induces a depletion of the lower, long-lived (~1 ms)level of the strong UV lines by photoionization. The subsequentrecombination of Fe III explains the appearance of the ``forest'' ofnarrow Fe II lines. The possibility of a cyclic process is alsodiscussed, where HLyalpha induces depletion to bound states, which havefast decays in the far-UV to the lower state of the Bowen pumpingchannel.
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| 3. |
- Johansson, Sveneric, et al.
(författare)
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Anomalous Fe II Spectral Effects and High H I Lyα Temperature in Gas Blobs Near η Carinae
- 2004
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Ingår i: Astronomy Letters. - : Pleiades Publishing Ltd. - 1063-7737 .- 1562-6873. ; 30:1, s. 58-63
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Tidskriftsartikel (refereegranskat)abstract
- We consider the origin of the anomalously high intensity of theultraviolet Fe II lambda 2507/2509 A lines observed with high spatialand spectral resolutions from gas blobs (GBs) near Carinae. This rareeffect in stellar spectra is attributable to a combination of severalfactors: (1) the high hydrogen density (>10^{8} cm^{-3}) that ensuresthe blocking of the Lyman continuum by GBs and, accordingly, theformation of a cold H I region with completely ionized Fe atoms; (2) thesmall distance between the GBs and the central star that ensures a high(>8000-10 000 K) Ly_alpha H spectral temperature, which photoexcitesFe II selectively; and (3) the population of Fe II levels and,accordingly, the opening of a stimulated emission channel, whichtogether with spontaneous transitions creates a radiative cycle where asingle Fe II ion can multiply absorb Ly_alpha emission.
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| 4. |
- Johansson, Sveneric, et al.
(författare)
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Anomalously bright UV lines of Fe II as a probe of gas condensations in the vicinity of hot stars
- 2003
-
Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 412, s. 771-776
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Tidskriftsartikel (refereegranskat)abstract
- Two UV lines of Fe II at 2507/2509 Å are extremely bright inspatially resolved HST/STIS spectra of dense gas condensations (the socalled Weigelt blobs) close to the central star of eta Carinae. Thelines also appear unresolved in HST/FOS spectra of the star AE And.Under normal conditions the lines should hardly be observable. Based onrecent studies of the formation of thelambdalambda2507/2509 lines as part of a radiative cycledriven by HLyalpha pumping and including stimulated emission wepropose the possibility of using them as a probe of non-homogeneities ingas condensations located outside hot, massive stars.
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| 5. |
- Johansson, Sveneric, et al.
(författare)
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Astrophysical laser operating in the OI 8446-angstrom line in the Weigelt blobs of eta Carinae
- 2005
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 1365-2966 .- 0035-8711. ; 364:2, s. 731-737
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Tidskriftsartikel (refereegranskat)abstract
- Within the framework of a simple model of photophysical processes in the Weigelt blobs in the vicinity of the luminous blue variable (LBV) star eta Carinae, we explain the presence of the fluorescent < O I > 8446-angstrom and forbidden [O I] 6300-angstrom lines as well as the absence of the allowed O I 7774-angstrom line in spectra recorded with the Hubble Space Telescope (HST)/STIS instrument (Gull et al.). From atomic data and estimated stellar parameters we demonstrate that there is a population inversion and stimulated emission in the 3p P-3-3s S-3 transition lambda 8446 due to photoexcitation by accidental resonance (PAR) by H Ly beta radiation.
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| 6. |
- Johansson, Sveneric, et al.
(författare)
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Astrophysical laser spectroscopy
- 2005
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Ingår i: Laser Spectroscopy, Proc. XVII International Conference. ; , s. 79-93
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Konferensbidrag (refereegranskat)
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| 7. |
- Johansson, Sveneric, et al.
(författare)
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Astrophysical lasers and nonlinear optical effects in space
- 2007
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Ingår i: New Astronomy Reviews. - : Elsevier BV. - 1872-9630 .- 1387-6473. ; 51:5-6, s. 443-523
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Forskningsöversikt (refereegranskat)abstract
- The present state of the art concerning astrophysical lasers (APL) and nonlinear optical effects under astrophysical conditions is reviewed. The operational conditions of an APL (amplification under non-LTE conditions) and astrophysical predecessors of the laboratory lasers are considered in the introduction of the review. The rareness of observed APL action in the visible range in comparison with astrophysical masers (APM) in the microwave range is explained. Early proposals of APLs with collisional and optical pumping are discussed. APL/M in the mid-IR and submillimeter ranges linking APL and APM are also discussed. APLs in the Weigelt blobs of Eta Carinae operating in Fell and 01 with a Bowen type optical pumping are considered in detail. General questions (narrowing of APL spectral lines, the possibility of scattering feedback and ways of measuring the true spectral width of an APL) are considered. Nonlinear optical effects in astrophysical conditions and resonance-enhanced two-photon conditions, in particular, are discussed in the conclusion. (C) 2007 Elsevier B.V. All rights reserved.
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| 8. |
- Johansson, Sveneric, et al.
(författare)
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Astrophysical lasers in optical Fe II lines in gas condensations near η Carinae
- 2005
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Ingår i: Atomic Physics 19. - : AIP. - 0094-243X .- 1551-7616. ; 770, s. 399-410
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Konferensbidrag (refereegranskat)abstract
- 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 Lyα pumped Fe II levels. The intense Lyα radiation is formed in the HII region of gas condensations close to the star η Car. The laser transitions form together with spontaneous transitions closed radiative cycles, one of which includes the extremely bright 2507/09 Å 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
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| 9. |
- Johansson, Sveneric, et al.
(författare)
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Astrophysical lasers operating in optical Fe II lines in stellar ejecta of η Carinae
- 2004
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Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 428, s. 497-509
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Tidskriftsartikel (refereegranskat)abstract
- After the discovery of space masers based on OH radicals (Weaver et al.cite{Wea65}) and H2O (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 CO2molecule 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.
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| 10. |
- Johansson, Sveneric, et al.
(författare)
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Astrophysical Lasers with Radiation Pumping by Accidental Resonance
- 2003
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Ingår i: Publications of the Astronomical Society of the Pacific. - : IOP Publishing. - 1538-3873 .- 0004-6280. ; 115:814, s. 1375-1382
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we consider a general problem of astrophysical lasersoperating with optical pumping by accidental resonance (PAR) with strongspontaneous emission lines of other elements. The origin of populationinversion and the coefficient of amplification due to the opticalexcitation of atoms (ions) by a four-level scheme with PAR are analyzed.We elucidate conclusively the question of the manifestation ofastrophysical lasers in the optical region of the spectrum, which inprinciple differs from that of astrophysical masers in the microwaverange.
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