Invited contribution at the 300th Symposium of the International Astronomical Union: "The Nature of Solar Prominences and their Role in Space Weather"

1. Plasma properties
in eruptive prominences
Nicolas Labrosse
University of Glasgow, Scotland, UK
With help from Scott Forrest

2. Motivation
Understanding how the prominence plasma evolves during an
eruption can shed light on
CME initiation mechanisms
Link between chromosphere and heliosphere
Outline
Effect of plasma motion on emergent radiation
Non-LTE modelling
Results for the He II 304 Å line
Comparison with SDO/AIA observations
Motivation and Outline
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3. Theoretical calculations have shown that when solar prominences
move away from the surface of the Sun, their radiative output is
affected via the Doppler dimming or brightening effects.
Hyder & Lites (1970), Heinzel & Rompolt (1987), Gontikakis et al (1997), Labrosse et al
(2007, 2008)
Doppler dimming (brightening) is the decrease (increase) in intensity
of a line formed by resonant scattering of the incident radiation from
the Sun due to the radial motion of the plasma.
Mostly strong resonance lines are affected by this effect.
Similar effect used to diagnose solar wind speed
Kohl & Withbroe (1982)
Effects of plasma motions on EPs radiation
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4. The prominence model
•1D plane-parallel vertical slab
Free parameters
Gas pressure
Temperature
Column mass
Height above the limb
Radial velocity
Equations to solve
Pressure equilibrium, ionisation and
statistical equilibria (SE), radiative
transfer (RT) for H (20 levels)
SE, RT for other elements: He I (29
levels) + He II (4 levels)
The prominence model
Multi-level, multi-line
non-LTE modelling
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5. Doppler dimming/brightening depends on
•Line formation mechanism
•Strength / shape of incident radiation
•Coupling with other energy states
•Coupling with other lines
Effects of plasma motions on EPs radiation
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V=0 km s-1
V=80 km s-1
V=200 km s-1
V=400 km s-1
5
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T = 8000 K T = 15000 K
Labrosse et al (2010)

6. 6
 He II 304 Å line sensitive to Doppler dimming
 line mostly formed by scattering of incident radiation
coming from the Sun
Plasma motions in prominences
Nicolas Labrosse - IAU Symposium S300, Paris11/06/2013Labrosse et al. (2007)

7. 7
Results (5)
Doppler dimming of He resonance lines stronger if:
Cool plasma
Not too dense
Large temperature
gradient in PCTR
Increasing column mass with all other parameters kept constant
means more hot material → collisional component becomes more
important ⇒ the line is less sensitive to Doppler dimming
Doppler dimming of He resonance lines
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Constant plasma parameters

8. Question
Is Doppler dimming observed in eruptive prominences?
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9. 9
2010-06-13
11/06/2013 Nicolas Labrosse - IAU Symposium S300, Paris
SDO/AIA observations

10. 10
2010-06-13
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SDO/AIA observations
2011-06-10

11. This study shows that...
Variation of He II 304 intensity with radial velocity
Decreases in some cases, increases in others
Comparison with non-LTE computations
Variation of plasma parameters and Doppler dimming effect
explain changes in He II 304 intensity
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Labrosse & McGlinchey (2012)

12. Eruption of 19 March 2011 observed by AIA
Plasma diagnostics
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13. Eruption of 19 March 2011 observed by AIA
Plasma diagnostics
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Surface pressure
decreases during
eruption as EP rises

14. Perspectives
Extreme Ultraviolet Imager
on Solar Orbiter
•Combining with in-situ data out of the ecliptic
•Better understanding of physical conditions within EPs
•Better understanding of links between EPs and dynamic heliosphere
•EUI will monitor the low atmosphere
counterparts of large-scale solar eruptive
events such as CMEs.
•It will ideally be suited to study
prominence eruptions.
•Using both H Ly-α and He II 304 lines will
add constraints on the models.
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15. Conclusions
•EP plasma parameters obtained
•minimizing differences between observables and model parameters
•New non-LTE models
•Explain intensity variations by changes in plasma parameters
•Are able to reproduce qualitatively SDO/AIA observations
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TAKK!

16. Royal Astronomical Society
Specialist Discussion Meeting
Friday 21st February 2014
London
The Life of Solar Prominences
Organisers:
Nicolas Labrosse
Duncan Mackay
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