| 1. |
- Hartman, Henrik, et al.
(författare)
-
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
-
Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 436:3, s. 945-952
-
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.
|
|
| 2. |
- Johansson, Sveneric, et al.
(författare)
-
Astrophysical laser operating in the OI 8446-angstrom line in the Weigelt blobs of eta Carinae
- 2005
-
Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 1365-2966 .- 0035-8711. ; 364:2, s. 731-737
-
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.
|
|
| 3. |
- Johansson, Sveneric, et al.
(författare)
-
Astrophysical laser spectroscopy
- 2005
-
Ingår i: Laser Spectroscopy, Proc. XVII International Conference. ; , s. 79-93
-
Konferensbidrag (refereegranskat)
|
|
| 4. |
- Johansson, Sveneric, et al.
(författare)
-
Astrophysical lasers in optical Fe II lines in gas condensations near η Carinae
- 2005
-
Ingår i: Atomic Physics 19. - : AIP. - 1551-7616 .- 0094-243X. ; 770, s. 399-410
-
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
|
|
| 5. |
- Johansson, Sveneric, et al.
(författare)
-
Metastable hydrogen absorption in ejecta close to eta Carinae
- 2005
-
Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 435:1, s. 183-189
-
Tidskriftsartikel (refereegranskat)abstract
- Spectroscopy with the high spatial resolution of the Hubble Space Telescope (HST) reveals narrow absorption in the hydrogen Balmer lines in spectra of Eta Carinae and the nearby nebular-scattered starlight. While hydrogen Balmer absorption lines are seen in stellar photospheres and winds, we are not aware of such being seen in galactic nebulae. This exceptional case is caused by intense stellar UV radiation acting on high-density neutral clumps of gas in the close vicinity of the central source. The interaction of the UV radiation with hydrogen results in photo-ionization and photo-excitation leading to a non-equilibrium population of the metastable 2s S-2 level. This occurs throughout the equatorial region surrounding eta Carinae in sufficient quantity to produce strong narrow absorption on top of the broad P Cygni emission profile. This absorption can be considered to be a probe of the very non-uniform ejecta in the disk region surrounding eta Carinae.
|
|
| 6. |
- Johansson, Sveneric, et al.
(författare)
-
Possibility of measuring the width of narrow FeII astrophysical laser lines in the vicinity of eta Carinae by means of Brown-Twiss-Townes heterodyne correlation interferometry
- 2005
-
Ingår i: New Astronomy. - : Elsevier BV. - 1384-1092 .- 1384-1076. ; 10:5, s. 361-369
-
Tidskriftsartikel (refereegranskat)abstract
- We consider the possibility of measuring the true width of the narrow Fe II optical lines observed in spectra of the Weigelt blobs in the vicinity of eta Carinae. The lines originate as a result of stimulated amplification of spontaneous emission of radiation in quantum transitions between energy levels showing inverted population [Johansson, S., Letokhov, V., 2002. JETP Lett. 75 (10) 495; Johansson, S., Letokhov, V., 2003. Phys. Rev. Lett. 90 (1) 01110-1; Johansson, S., Letokhov, V., 2004. A&A 428, 497]. The lines should have a subDoppler spectral width of 30-100 MHz, depending on the geometry of the lasing volume. To make measurements with a spectral resolution of R > 10(7) and an angular resolution better than 0.1 '', we suggest the use of the Brown-Twiss-Townes optical heterodyne intensity correlation interferometry. The estimates made of the SIN ratio for the optical heterodyne astrophysical laser experiment imply that it is feasible.
|
|
| 7. |
- Johansson, Sveneric, et al.
(författare)
-
Stimulated amplification in an astrophysical plasma: An FeII space laser in gas condensation in the vicinity of eta carinae
- 2005
-
Ingår i: Laser Physics. - 1054-660X. ; 15:7, s. 939-946
-
Tidskriftsartikel (refereegranskat)abstract
- We consider the conditions necessary for the development of an inverted population among the energy levels of free atoms in a medium exposed to radiation in spectral nonequilibrium. In particular, we focus on monochromatic radiation occurring as a result of an accidental wavelength coincidence between a pumping emission line and a pumped absorption line in two different elements. We examine especially the influence of "pseudometastable" states (at medium excitation) in the complex spectrum of Fe 11, which cause a "bottleneck" in the radiative decay leading to an inverted level population. We also discuss the effect of spectral compression of the Lyman continuum into H Ly-alpha radiation at a high effective temperature. In conclusion, we describe those differences between microwave astrophysical masers (APM) and optical astrophysical lasers (APL) that make the latter a more rare phenomenon in nature.
|
|
| 8. |
|
|
| 9. |
- Johansson, Sveneric, et al.
(författare)
-
Stimulated amplification under spatially nonhomogeneous conditions: An astrophysical FeII laser in the vicinity of eta carinae
- 2005
-
Ingår i: Physica Scripta. - 0031-8949. ; T120, s. 99-104
-
Tidskriftsartikel (refereegranskat)abstract
- We consider the conditions necessary for the development of an inverted population among the energy levels of free atoms in a medium exposed to radiation in spectral non- equilibrium. In particular, we focus on monochromatic radiation occurring as a result of an accidental wavelength coincidence between a pumping emission line and a pumped absorption line in two different elements. We examine especially the influence of "pseudo-metastable" states ( at medium excitation) in the complex spectrum of Fe II, which cause a "bottleneck" in the radiative decay leading to an inverted level population. We also discuss the effect of "spectral compression" of the Lyman continuum into HLy alpha radiation at a high effective temperature. In conclusion we describe those differences between microwave astrophysical masers (APM) and optical astrophysical lasers (APL) that make the latter a more rare phenomenon in Nature.
|
|
