Observational Evidence for Cross-field Diffusion of Neutral Filament Material

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Observational Evidence for Cross-field Diffusion
of Neutral Filament Material

• Holly Gilbert Gary Kilper
• Rice University
• 10/29/07

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Motivation..
Some relevant questions regarding the
relationship between CMEs and prominences

• Do prominences act as anchors?
• Does mass loss in prominences initiate CMEs?
• Does prominence density, magnetic structure, and
  pre-eruptive dynamics tell us something
  fundamental about the magnetic structure and
  available energy of the CME?

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Approach to addressing those questions.

• Determine total prominence mass
• Determine how much mass is being lost and how
  much is replinished
• Understand which mechanisms are responsible for
  mass variation
• Once identified, determine the relative
  importance of those mechanisms
• Find spatial and temporal variation of mass

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Obtaining total prominence mass
Extinction factor
Prominence mass loss could be important in CME
initiation!!
Column density

• mean absorption cross section
• ntotal prom. number density
• mmean mass per particle

(Assume ? is constant through prominence)
Total prominence mass
Results
Average mass of quiescent prominences is
Average mass of eruptive prominences is
Mass of a typical CME 1015 1016 g
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Mass loss via. Cross field diffusion? (Gilbert et
al. 2002 2007)
Simple Prominence Support Models
Flux-rope model
Dip Model
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Force Balance in a Multi-Constituent Prominence
Plasma
General Momentum Balance Equation ( jth particle
species)
EXAMPLE Proton Force Balance
z-component
y-component
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Time Scales for Neutral Atom Loss
General Relations
Loss Times for Helium and Hydrogen
1 day
Helium
22 days
Hydrogen
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Initial Comparison of H and He Observations
He I (l1083 nm)
Ha (l656 nm)
Ha (l656 nm)
He I (l1083 nm)
He I (l1083 nm)
Ha (l656 nm)
Ha (l656 nm)
He I (l1083 nm)
He I (l1083 nm)
Ha (l656 nm)
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Quantitative Analysis

• Study temporal and spatial Changes in the
  relative H and He in filaments via the absorption
  and He I / Ha absorption ratio
• Chose different types of filaments large/stable,
  small/stable, eruptive that could be followed
  across the solar disk
• Used co-temporal Ha (6563 Å) and He I (10830 Å)
  images from the Mauna Loa Solar Observatory in
  2004
• Kilper (Masters thesis) Developed an IDL code
  that scales and aligns each pair of images,
  selects the filament, and calculates the
  absorption ratio at every pixel
• Alignment of images is key to a pixel-by-pixel
  comparison

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He/H absorption
Darker pixel ? Helium deficit Brighter pixel ?
Helium surplus
Edge effects
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Large stable
January 2004
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1/19 1744
1/19 2343
1/20 1812
1/21 0206
January 2004
small stable
October 2004
10/15 1654
10/15 2246
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May 2004
Partial eruption Absence of edge effects
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What do we expect??
Geometrical considerations the simplest picture
Cylindrical representation of a filament
Filament axis
Larger vertical column density
View along filament axis
Small vertical column density
Dark relative He deficit
Top view at disk center
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Somewhat more realistic geometry
Dark relative He deficit
Top edge with dark band
Top edge with dark band
Bottom edge with white bands
Bottom edge with white bands
White relative He surplus
Observed near east limb
west limb
center disk
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Interpretation of Edge effects

• Far from disk center, one edge is at the top,
  and one at the bottom (where the barbs appear)
• In a relatively stable filament, He drains out
  of the top rapidly (relative He deficit)
• He draining out of bottom is replaced by He
  draining down from above (no relative He deficit)

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How does the absorption ratio vary on shorter
time scales??
And what about eruption??
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Erupting Filament
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Diffusion timescales In the context of filament
threads..
Coronal plasma in between threads
Coronal plasma can readily ionize neutral
material draining into it
Expect very short draining timescales.. However
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Coronal plasma in between threads
For high density filament threads, draining
timescale will not be too small it depends on
vertical column density
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Ongoing related work

• Study prominence absorption in coronal lines Fe
  XII 195 Å (SOHO/EIT, TRACE), and Mg X 625 Å
  (SOHO/CDS) to obtain relative mass abundances
  (Gilbert, Kilper, Kucera, in preparation)
• Investigate the absorption gradient visible in
  195 (i.e., initial results show the absorption is
  deeper at the bottom- another observational
  indication of cross-field diffusion?)
• Distinguish between gravitational settling and
  cross-field diffusion in observations
• Estimate fraction of prominence mass lost and
  determine how this is related to CMEs