Ion-neutral Coupling in Prominences

Transcription

1 infer about the magnetic structure? Ion-neutral Coupling in Prominences Motivation: Observations of vertical flows: do ion-neutral interactions play a role? By understanding the coupling what can we

2 LASCO C2 on January 4, 2002 Extreme ultraviolet Imaging Telescope (EIT) 304Å on February 2, 2001 SDO AIA composite made from three of the AIA wavelength bands, corresponding to temperatures from.7 to 2 million degrees (hotter = red, cooler = blue).

3 Prominences Filaments o o o Length ~ Mm, Height ~ Mm, Width ~ 1-10 Mm (1 Mm = 1000 km = 10 8 cm) Lifetime ~ hours - months T < 10 4 K, N ~ cm -3, M ~ gm o V ~ km s -1

4 Approach o Determine whether cross-field diffusion of neutrals is important-- initial calculation of Gilbert et al. (2002)! o Look to observations to support findings (2007, 2010)! o Study spatial and temporal variation of mass in different lines o Determine relative importance of mechanisms responsible o for mass variation!

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

6 Force Balance in a Multi-Constituent Prominence Plasma General Momentum Balance Equation ( j th particle species) t GM ( ) ( ) ( ) ρ u + ρ u u = p τ + n ez E + u B ρ eˆ 2 " j j j j j j j j j j j r ( ) + ρ j ν j k uk u j + F k R j + FT j + m # $ j & P k j kuk ju Lj ' Other assumptions:! o Neglect flows along the magnetic field o Constant density and temperature throughout system o Collision frequencies appropriate for subsonic flow speeds (our calculated flow speeds are less than 0.1 km s -1 ) o Local magnetic field is exactly horizontal to the (locally flat) solar surface r

7 EXAMPLE: Proton Force Balance z-component: y-component: ( ) ( ) u g % u u u u + ν ( u ) ( ) p He He z u p z + ν u u + + " p He He z p z $ 1 p y = Ωp + Ω $ p ν pe e z p z + ν p H H z p z ( ) ( ) u % u u u u + ν ( u ) ( ) p He He y u p y + ν u u + + " p He He y p y $ 1 p z = Ω $ p ν pe e y p y + ν p H H y p y B = Bê x! g = -ê z GM/r 2!! Ω j = Z j eb/m j

8 Perpendicular Flow in a H-He Prominence Plasma g B z g y u H y He y u u p y u + He y u e y x B u p z u + He z u e z u H z u He z

9 Parameter Study Considered dependence of particle velocities on variation of several parameters (reference values in parentheses): o Total atom density (10 10 cm -3 ) o Helium abundance by number (0.1) o H and He ionization fractions (0.5 and 0.1) o Temperature (7 x 10 3 K) o Magnetic field (10 G)

10 log 10 [ u z (cm s -1 ) ] (a) Total Atom Density He H log 10 [ n (cm -3 ) ] (b) Helium Abundance He H Helium Abundance by Number log 10 [ u z (cm s -1 ) ] 6 5 (c) Hydrogen Ionization He H Hydrogen Ionization Fraction (d) Helium Ionization He H Helium Ionization Fraction log 10 [ u z (cm s -1 ) ] He H (e) Temperature Temperature (T in units of 10 3 K) 6 5 (f) Magnetic Field He H Magnetic Induction (B in units of Gauss)

11 General Relations Time Scales for Neutral Atom Loss ( h prom = vertical prominence dimension) τ He hprom uhe τ H hprom uh u He! 10 cm " 10 # $ cm s u H! 10 cm " 5 10 # $ cm s #' $ ( ( -3 # n cm ) & $ ( -3) ' n cm Loss Times for Helium and Hydrogen τ Helium: He ( ) ( -3 R n cm ) " h # " # $ % $ % ' ( $ ' % ( prom sun 24 hours R sun 10 cm = 1 day Hydrogen: τ H ( ) ( -3 R n cm ) " h # " # $ % $ % ' ( $ ' % ( prom sun 520 hours R sun 10 cm ~ 22 days

12 Hα (λ=656 nm) January 30, 2000, 20:11:22 UT He I (λ=1083 nm) January 30, 2000, 20:10:15 UT Both Images from the HAO Mauna Loa Solar Observatory

13 Initial Comparison of H and He Observations Hα (λ=656 nm) He I (λ=1083 nm) Hα (λ=656 nm) Hα (λ=656 nm) He I (λ=1083 nm) Hα (λ=656 nm) He I (λ=1083 nm) He I (λ=1083 nm) Hα (λ=656 nm) He I (λ=1083 nm)

14 Quantitative Analysis Study temporal and spatial Changes in the relative H and He in filaments via the absorption and He I / Hα absorption ratio Chose large/stable and small/stable filaments that could be followed across the solar disk! Used co-temporal Hα (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

15 He/H absorption Darker pixel Helium deficit Brighter pixel Helium surplus Edge effects

16 January 2004 Large & stable

17 May 2004 Partial eruption: Absence of edge

18 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 Top view at disk center Dark = relative He deficit

19 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 center disk west limb

20 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

21 Diffusion timescales In the context of filament threads.. Coronal plasma in between threads τ τ He H ( ) ( -3 R n cm ) " h # " # $ % $ % ' ( $ ' % ( prom sun 24 hours R sun 10 cm ( ) ( -3 R n cm ) " h # " # $ % $ % ' ( $ ' % ( Coronal plasma can readily ionize neutral material prom sun 520 hours R sun 10 cm draining into it Expect very short draining timescales (for threads with small vertical neutral atom column density)