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Chromospheric Evaporation

Chromospheric Evaporation. Peter Gallagher University College Dublin Ryan Milligan Queen’s University Belfast. Canonical Flare Model. Step 1: Acceleration. Reconnection produces power-law electron distribution. Step 2: Propagation.

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Chromospheric Evaporation

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  1. Chromospheric Evaporation Peter Gallagher University College Dublin Ryan Milligan Queen’s University Belfast Peter Gallagher (UCD)

  2. Peter Gallagher (UCD)

  3. Canonical Flare Model • Step 1: Acceleration. • Reconnection produces power-law electron distribution. • Step 2: Propagation. • Electrons spiral along magnetic fields from corona to chromosphere. • Step 3: Heating. • Electrons deposit energy in chromosphere via Coulomb collisions. • Step 4: Evaporation. • Dense chromosphere radiates and may expand. Peter Gallagher (UCD)

  4. T1: Nonthermal Electrons T3: VUP T2: Impulsive Heating T3: VDOWN Chromospheric Response • How does the chromosphere respond to nonthermal electrons? • Assume power-law electron spectrum: • f(E) ~ E-electrons cm-2 s-1 Loop leg Density Peter Gallagher (UCD)

  5. Chromospheric Response • Chromospheric response depends on properties of accelerated electrons: • Low-energy cut-off (Ec) • Lower Ec=> more energy => more rapid and pronounced response. • Power-law index () • Harder spectrum => high energy electrons penetrate deeper where chromospere better able to radiate => less rapid and pronounced response. • Total flux • Higher flux => more energy => more rapid and pronounced response. EC f(E) thermal nonthermal  E Peter Gallagher (UCD)

  6. Gentle vs Explosive Evaporation Peter Gallagher (UCD)

  7. Gentle vs Explosive Evaporation Peter Gallagher (UCD)

  8. Peter Gallagher (UCD)

  9. Peter Gallagher (UCD)

  10. RHESSI Spectral Coverage Peter Gallagher (UCD)

  11. CDS and TRACE: 26 March 2002 Flare • SOHO/CDS • He I (0.03 MK) • O V (0.25 MK) • Mg X (1.1 MK) • Fe XVI (2.5 MK) • Fe XIX (8 MK) • TRACE 17.1 nm • Fe IX/X (1.0 MK) Peter Gallagher (UCD)

  12. RHESSI Integrated Spectrum Peter Gallagher (UCD)

  13. Footpoint Downflows • Loops are not static. • Downflows <50 km s-1, upflows >100 km s-1 • Loops cool via conduction, radiation, and flows. Peter Gallagher (UCD)

  14. M2.2 Flare – CDS/EIT/GOES Peter Gallagher (UCD)

  15. M2.2 Flare – CDS/EIT/GOES Peter Gallagher (UCD)

  16. RHESSI Lightcurve Peter Gallagher (UCD)

  17. RHESSI Spectrum • Thermal: • T ~ 20 MK • EM ~ 1049cm-3 • Nonthermal: • Ec ~ 24 keV • ~ 7.3 • HXR Area <1018cm2 • => Nonthermal Electron Flux >3x1010 ergs cm-2 s-1 Peter Gallagher (UCD)

  18. 6 - 12 keV (dashed line) Thermal 25 – 50 keV (solid line) Non-thermal Peter Gallagher (UCD)

  19. Stationary Fe XIX Component Blueshifted Fe XIX Component Evidence for Upflows Doppler shifts measured relative to a stationary component: v/c = (- 0)/ 0 In Fe XIX v = 270 km s-1 Peter Gallagher (UCD)

  20. Flow velocity vs. Temperature Peter Gallagher (UCD)

  21. Future Work • How does the chromospheric response depend on the nonthermal electron properties? • We only have one event! • Nonthermal electrons => F>3x1010 ergs cm-2 s-1 • Response => ~ -30 km s-1 and 270 km s-1 • Is there a threshold for explosive evaporation? • Heating < expansion => 3kT / Q < L/cs • => need large number of CDS/RHESSI flares Peter Gallagher (UCD)

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