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| 2. |
- Bautista, M A, et al.
(författare)
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Excitation of Sr II lines in Eta Carinae
- 2002
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 1365-2966 .- 0035-8711. ; 331:4, s. 875-879
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Tidskriftsartikel (refereegranskat)abstract
- We study the nature of the peculiar [Sr II] and Sr II emission filament found in the ejecta of Eta Carinae. To this purpose we carry out abinitio calculations of radiative transition probabilities and electron impact excitation rate coefficients for Sr II. Then we build a multilevel model for the system which is used to investigate the physical condition of the filament and the nature of the observed allowed and forbidden Sr II optical emission. It is found that the observed spectrum is consistent with the lines being pumped by the continuum radiation field in a mostly neutral region with electron density near 107cm-3 . Under these conditions, the observed emission can be explained without the need for a large Sr overabundance.
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| 3. |
- Gull, T. R., et al.
(författare)
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The Strontium Filament within the Homunculus of Eta Carinae
- 2001
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Ingår i: Bulletin of the American Astronomical Society. ; 33:4, s. 1505-1505
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Konferensbidrag (refereegranskat)abstract
- During a series of HST/STIS observations of Eta Carinae and associatedejecta, we noticed a peculiar emission filament located a few arcsecondsnorth of the central source. While bright in nebular standards, it issubmerged in a sea of scattered starlight until moderately highdispersion, long-slit spectroscopy with the STIS (R 8000) brings theemission lines out. The initial spectrum, centered on 6768A with theSTIS G750M grating, led to identification of twenty lines fromsingly-ionized species including [Sr II], [Fe II], [Ti II], [Ni II], [MnII], and [Co II] (Zethson, etal., 2001, AJ 122, 322). No Balmer emissionis detected from this filament and the Fe II 2507,9 lines, known to bepumped by Lyman alpha radiation in other regions near the centralsource, are not detected. Followup observations have led to detection ofhundreds more emission lines from iron group elements in neutral andsingly-ionized states. Thus far all are excited by less than 10 eV. Thispeculiar nebular emission is thought to be due to very intense stellarradiation, stripped of uv flux shortward of Lyman alpha, bathing aneutral structure. We are systematically identifying the many lines(over 90% identified) and measuring line intensities that will then bemodeled to determine excitation mechanisms, temperature and density. Two[Sr II] and two Sr II lines have now been measured. Bautista, etal. (inpreparation) have modeled the strontium flux ratios and find that largeradiation fluxes and/or high strontium abundances may account for thedetected emission. These observations were supported by STIS GTO fundingand GO funding through the STScI.
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| 4. |
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| 5. |
- Verner, E. M., et al.
(författare)
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The origin of Fe II and [Fe II] emission lines in the 4,000-10,000 Å range in the BD Weigelt Blobs of Eta Carinae
- 2002
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 581:2, s. 1154-1167
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Tidskriftsartikel (refereegranskat)abstract
- We present numerical simulations that reproduce the salient features of the amazingly strong [Fe ii andFe ii emission spectra in the B and D Weigelt blobs of Carinae. For our studies we have used spectraobtained during the 1998 epoch observations with the Hubble Space Telescope (HST). The spectrum of the Band D Weigelt blobs dominates in [Fe ii and Fe ii emission lines. The same observations show no Fe i orFe iii. We have compared our measurements of the strongest (200) [Fe ii and Fe ii lines and blends in thespectrum with theoretical predictions. Our predictions are based on non-LTE modeling of the Fe ii atom,which includes the lowest 371 energy levels (all levels up to 11.6 eV). We have investigated the dependence ofthe spectrum on electron density, pumping by the blackbody-like stellar continuum, and intense Lyemission. We nd that radiative pumping is essential in explaining the observed spectrum. We have identiedthe main pumping routes responsible for the observed Fe ii emission. Comparison between the model andobservations reveals details of the radiation eld. Pumping by the blackbody-like stellar radiation eld from Carinae explains the numerous strong [Fe ii and Fe ii lines in the range of 40006500 . The strongest Fe iilines in a range of 800010000 are pumped by intense Ly radiation.
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| 6. |
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| 7. |
- Zethson, Torgil, et al.
(författare)
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Sr II and [Sr II] Emission in the Ejecta of eta Carinae
- 2001
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Ingår i: The Astronomical Journal. - : American Astronomical Society. - 1538-3881 .- 0004-6256. ; 122:1, s. 322-326
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Tidskriftsartikel (refereegranskat)abstract
- We have discovered four extremely surprising emission lines of strontiumin ejecta near eta Carinae. Hubble Space Telescope (HST) SpaceTelescope Imaging Spectrograph (STIS) observations made in 1999 show twonarrow features whose wavelengths correspond to the forbiddentransitions of Sr II, and we have found no other plausibleidentification for these lines. The identifications are confirmed by newHST/STIS observations of the same stellar position, in which the Sr IIresonance lines are observed. Moreover, [Ti II, [Ni II, [Mn II, and[Co II lines are unusually strong relative to [Fe II at the sameposition. Based on observations made with the NASA/ESA Hubble SpaceTelescope and supported by STIS IDT GTO 8036 and grant GO 8327 from theSpace Telescope Science Institute. The STScI is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS 5-26555.
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