Observational Evidence for Cross-field Diffusion of Neutral Filament Material Holly Gilbert & Gary Kilper Rice University 10/29/07

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? Motivation…..

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

 = e -  n  ds N =  n ds N = -  -1 ln  M p = m  N da  1.3m H N A eff Obtaining total prominence mass… Extinction factor Column density Total prominence mass Results: Average mass of quiescent prominences is Average mass of eruptive prominences is Mass of a typical CME: ~10 15 – g (Assume  is constant through prominence)  = mean absorption cross section n=total prom. number density m=mean mass per particle Prominence mass loss could be important in CME initiation!!

z y x B g Dip Model Flux-rope model Simple Prominence Support Models Mass loss via. Cross field diffusion? (Gilbert et al. 2002; 2007)

Force Balance in a Multi-Constituent Prominence Plasma General Momentum Balance Equation ( j th particle species) EXAMPLE: Proton Force Balance z-component: y-component:

Perpendicular Flow in a H-He Prominence Plasma z y x B g g  B

Time Scales for Neutral Atom Loss Loss Times for Helium and Hydrogen Helium: Hydrogen: General Relations = 1 day ~ 22 days

H  ( =656 nm) He I ( =1083 nm) H  ( =656 nm) Initial Comparison of H and He Observations

Quantitative Analysis Study temporal and spatial Changes in the relative H and He in filaments via the absorption and He I / H α absorption ratio Chose different types of filaments: large/stable, small/stable, & eruptive that could be followed across the solar disk Used co-temporal H α (6563 Å) and He I (10830 Å) images from the Mauna Loa Solar Observatory in 2004 Kilper (Master’s 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

He/H absorption Darker pixel ↔ Helium deficit Brighter pixel ↔ Helium surplus “Edge effects”

January 2004 “Large & stable”

10/15 16:5410/15 22:46 1/19 17:441/19 23:431/20 18:121/21 02:06 January 2004 October 2004 “small & stable”

May 2004 Partial eruption: Absence of “edge effects”

Top view at disk center Cylindrical representation of a filament View along filament axis Larger vertical column density Small vertical column density Filament axis What do we expect?? Geometrical considerations: the simplest picture Dark = relative He deficit

Bottom edge with white bands Top edge with dark band Bottom edge with white bands Somewhat more realistic geometry Dark = relative He deficit White = relative He surplus Observed near east limb center disk west limb

Interpretation of “Edge effects” Far from disk center, one edge is at the top, and one at the bottom (where the barbs appear) 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) 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) He draining out of bottom is replaced by He draining down from above (no relative He deficit)

How does the absorption ratio vary on shorter time scales?? And what about eruption??

Erupting Filament

Eruption ~22:30 UT Filament : Average He/H Ratios He I/H  Ratio UTC Time 14:00 16:00 18:0020:0022:0000:00 02: Aug Aug. 12

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……

Coronal plasma in between threads For high density filament threads, draining timescale will not be too small– it depends on vertical column density

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) 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?) 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 Distinguish between gravitational settling and cross-field diffusion in observations Estimate fraction of prominence mass lost and determine how this is related to CMEs