Presentation given at the 4th France-China Solar Physics Meeting, 15-18 November 2011, Nice

1. Plasma diagnostic in eruptive
prominences from SDO/AIA
observations at 304 Å
Nicolas Labrosse and Kristopher McGlinchey
University of Glasgow, Scotland, UK

2. Motivation
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)
This is due to their strong sensitivity to the incoming radiation from the solar disc.
He II resonance lines are mostly formed by scattering of the incident radiation under
typical quiescent prominence conditions.
Can we find observational signatures of the changes in the radiative
output of eruptive prominences in EUV observations at 304 Å?
What are the plasma parameters in eruptive prominences?
We analyse SDO/AIA observations and compare them with new non-
LTE radiative transfer calculations of the He II 304 Å line intensity in
eruptive prominences.

3. The prominence model
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)

4. Effects of radial motions
Effects of radial motions
•For a simple 2-level atom with photo-excitation
–Doppler dimming if the incident line is in emission
–Doppler brightening if the incident line is in absorption
•If coupling between several atomic levels
–situation gets more complex: dimming and brightening
–e.g. coupling between first two excited levels of H
•Factors determining effects of radial motions
–line formation mechanism (resonant scattering, thermal processes)
–details of incident radiation (strength, emission/absorption)
See Labrosse et al (2010)
4

5. V=0 km s-1
V=80 km s-1
T = 8000 K
T = 15000 K
V=200 km s-1
V=400 km s-1
He I 584 He II 304 He I 10830 Labrosse et al. (2007)

6. Plasma motions in prominences
 He II 304 Å line sensitive to Doppler dimming
 line mostly formed by scattering of incident radiation
coming from the Sun
Labrosse et al. (2007) 6

7. Results (5)
Initial results
Doppler dimming effect on Helium resonance lines
stronger if:
Cool plasma
Not too dense
Large temperature
gradient in PCTR
NB: Plasma parameters
are kept constant
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
7

8. Question
Is Doppler dimming observed in eruptive prominences?

9. SDO/AIA observations
2011-06-10
2010-09-08
9

10. Summary of observations
Variation of He II 304 intensity with radial velocity
Decreases in some cases, increases in others
How is this related to the pure Doppler dimming effect?
Need new computations
Allow plasma parameters to vary during eruption
Randomly chosen input parameters (within limits)

11. New computations
Reference model
T=8800 K
M=4.8 10-5 g cm-2
Solid line
Effect of Doppler
dimming alone (no
variation of plasma
parameters)
Equal proportion of models showing computed intensities in the He II
line either greater or lower than the intensity of the reference (static) model.
11

12. Summary
•Observations show either a decrease or an increase of intensity with
radial velocity.
•New non-LTE models explain the different behaviour of the
intensities by changes in the plasma parameters inside the
prominence, in particular the column mass of the plasma and its
temperature.
•These new non-LTE models are more realistic than what was used
in previous calculations as they allow all plasma parameters to vary.
•They are able to reproduce qualitatively the range of observations
from SDO/AIA.
Labrosse & McGlinchey (accepted in A&A)

13. Velocity vs. time

14. Model parameters