| 1. |
- Andersson, L-O, et al.
(author)
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A new neutron beam facility
- 2004
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In: Proc. of the 9th European Particle Accelerator Conference.
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Conference paper (peer-reviewed)
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| 4. |
- Gull, T. R., et al.
(author)
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The Strontium Filament within the Homunculus of Eta Carinae
- 2001
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In: Bulletin of the American Astronomical Society. ; 33:4, s. 1505-1505
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Conference paper (peer-reviewed)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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| 6. |
- Johansson, Sveneric, et al.
(author)
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New forbidden and fluorescence Fe III lines identified in HST spectra of eta Carinae
- 2001
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In: Astronomy and Astrophysics. - 1432-0746. ; 361, s. 977-977
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Journal article (peer-reviewed)abstract
- We discuss the origin of eight emission lines in the spectra of gas blobs close to the central star of eta Carinae. The spectra have been obtained with the Goddard High Resolution Spectrograph (GHRS) and the Space Telescope Imaging Spectrograph (STIS) onboard the Hubble Space Telescope. Between 2400 and 2500 Å five narrow lines are identified as new forbidden lines of doubly ionized iron, [Fe III]. We present gA-value data for the corresponding transitions, which combine two different metastable configurations of Fe III. An anomalous intensity of the narrow Fe III line (UV 34) at 1914 Å is explained as fluorescence due to HLyalpha pumping. A level mixing of about 1% increases the f-value of the pumped excitation channel by more than two orders of magnitude, which makes the pumping efficient and the fluorescence significant. We introduce a new designation for fluorescence lines photoexcited by an accidental resonance, eg. < Fe III> in the case of doubly ionized iron. Based on observations with the NASA/ESA Hubble Space Telescope, and supported by grant numbers GO-6501 and GO-7302 from the Space Telescope Science Institute. The STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.
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| 8. |
- Bautista, M A, et al.
(author)
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Excitation of Sr II lines in Eta Carinae
- 2002
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In: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 1365-2966 .- 0035-8711. ; 331:4, s. 875-879
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Journal article (peer-reviewed)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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| 9. |
- Bautista, M., et al.
(author)
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Continuum Fluorescence Excitation of Sr II in Eta Carinae
- 2001
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In: Eta Carinae and Other Mysterious Stars: The Hidden Opportunities of Emission Spectroscopy, ASP Conference Proceedings, Vol. 242. Edited by Theodore R. Gull, Sveneric Johannson, and Kris Davidson. San Francisco: Astronomical Society of the Pacific, ISBN: 1. ; , s. 111-111
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Conference paper (peer-reviewed)
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