The document discusses fluorescence and resonant ionization processes in Eta Carinae, an astrophysical laboratory. It describes how fluorescence produces emission lines in spectra of the Weigelt blobs near Eta Carinae. Resonance enhanced two-photon ionization (RETPI) can explain the formation of strongly varying emission lines through a process involving hydrogen Lyman lines. RETPI can control the ionization equilibrium of ions during periods of high radiation from the central star. These fluorescence and RETPI processes must be considered when using emission line ratios to determine physical conditions in astrophysical plasmas.

1. L U N D UN I V E R S I T Y
Fluorescence and resonant ionization in Eta Carinae
- an astrophysical laboratory
Henrik Hartman, Lund University, Sweden
Current Development in Atomic, Molecular and Optical Physics, Delhi 2011
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2. L U N D UN I V E R S I T Y
Laboratory Astrophysics @ Lund University
- Stellar high resolution spectroscopy (VLT; HST)
- High-resolution FTS measurements of dishcarges (Edlén lab)
- Lifetime measurements: LIF on laser produced plasmas (LLC)
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3. L U N D UN I V E R S I T Y
Collaborators
Lund/Malmö: H.Nilsson, H.Lundberg, L.Engström, S.Huldt, T.Lennartsson,
T.Brage, P.Jönsson, N.Ryde, (S.Johansson & V.Letokhov)
Eta Carinae: T.Gull (NASA), M.Bautista, V.Fivet (U Mich), J.Groh(MPIfI)
Lifetimes: E.Biemont group (th, Liege), S.Mannervik group (exp, Stockholm)
Thanks to:
CDAMOP2011 organizers
Swedish Science Council (VR),
Swedish National Space Board (SNSB) Johansson & Letokhov (deceased 2009)
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4. L U N D UN I V E R S I T Y
Outline
- Introduction, Eta Carinae
- Fluorescence
- Selective ionization (RETPI – Resonance Enhanced Two-Photon
Ionization) for SiIII and FeIII
- Outlook
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5. L U N D UN I V E R S I T Y
Eta Carinae
Homunculus
Central stars
Strontium filament
Weigelt blobs
10”
1” HST / WFPC2 image
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6. L U N D UN I V E R S I T Y
5.54 year periodicity observed in X-ray
RXTE-obsverations, courtesy of M.Corcoran.
K. Nielsen
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7. L U N D UN I V E R S I T Y
Eta Carinae
Maximum state
– the radiation from the central
star is driving the
photoprocesses in the Weigelt
condensation.
Minimum state
– the radiation from the central
star is blocked for several
months. The transition into the
minimum is referred to as the
spectroscopic event.
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8. L U N D UN I V E R S I T Y
The Bowen mechanism (fluorescence)
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9. L U N D UN I V E R S I T Y
Fluorescence lines in HST spectra of WB
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10. L U N D UN I V E R S I T Y
Temporal variations of HI and FeII lines
The temporal variations during the
spectroscopic event is different for
different kinds of lines.
Hydrogen lines and fluroescent
lines vary quicker, whereas the
(most) forbidden lines excited by
collisions have a much slower
response set by the recombination
time scale, i.e. removal of
electrons.
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11. L U N D UN I V E R S I T Y
Variations of SiIII] 1892 Å line
maximum Spatial scale
minimum
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12. L U N D UN I V E R S I T Y
Variations of SiIII] 1892 Å line
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13. L U N D UN I V E R S I T Y
RETPI of Si+, enhancing the 1892Å SiIII] line
The 2-photon process involving HLyα
and HLyγ leaves the atom doubly
ionized and in an excited state,
producing the 1892 Å radiation as it
decays.
Johansson & Letokhov, Science (2001)
Johansson, Hartman, Letokhov A&A (2006)
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14. L U N D UN I V E R S I T Y
Estimation of the RETPI rate in the Weigelt blobs
The 2-photon process involving HLyα
and HLyγ depends on the difference
between the real level and the virtual
level, and in the intensity of the H
Lyman lines.
With estimates of the conditions in the
WB, the observed intensity of the
1892 Å feature, 7x10-12 erg cm-2 s-1 Å-1,
can be explained buy the RETPI
process.
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15. L U N D UN I V E R S I T Y
Ionization balance in the Weigelt blobs
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16. L U N D UN I V E R S I T Y
Possibilities for RETPI producing [FeIII]
The double H Lyα energy corresponds to
the difference between the 3d5(6S) 4s 5S in
FeIII and 3d6(5D) 4s 4D in FeII, with the 5p
levels in between.
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17. L U N D UN I V E R S I T Y
Conclusion and outlook
• In the Weigelt blobs of Eta Carinae (as in many other astrophysical plasmas),
fluorescence is an important process for line formation. The temporal variations in the
incident radiation from the central star allow us to study these processes separate from
the collisional excitation and ionization.
• The same HST spectra indicate that RETPI (Resonance Enhanced Two-Photon
Ionization) can be responsible for the formation of strongly varying lines. During the
high state (maximum), the RETPI process can control the ionization equilibrium for
many ions.
• RETPI often leaves the ions in an excited state. With the RETPI producing strong
forbidden lines, e.g. Si III] and [FeIII], care must be taken when using simple line
rations for determination of physical conditions.
• Forbidden lines are often strong and used for diagnostics in emission line objects like
stellar winds, AGNs and Quasars. Eta Carinae is an ideal and rare object to study
these processes, but the importance of these processes are probably much wider.
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