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Chromospheric Evaporation

Chromospheric Evaporation. Peter Gallagher University College Dublin Ryan Milligan Queens University Belfast. Chromospheric Evaporation. Non-thermal electrons supply the necessary energy to heat the plasma and cause flows . E nonthermal -> E thermal + E kinetic. T 1 : Nonthermal

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Chromospheric Evaporation

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  1. Chromospheric Evaporation Peter Gallagher University College Dublin Ryan Milligan Queens University Belfast Peter Gallagher (UCD)

  2. Chromospheric Evaporation • Non-thermal electrons supply the necessary energy to heat the plasma and cause flows. Enonthermal -> Ethermal + Ekinetic Peter Gallagher (UCD)

  3. T1: Nonthermal Electrons T3: Vup<1000 km/s T2: Impulsive Heating T3: VDOWN<100 km/s Chromospheric Response • How does the chromosphere respond to nonthermal electrons? • Assume power-law electron spectrum: • F(E) ~ (E/Ec)- electrons cm-2 s-1 • Chromospheric response depends on properties of accelerated electrons: • Low-energy cut-off (Ec). • Power-law index (). • Total flux. Loop leg Density Peter Gallagher (UCD)

  4. Explosive • Chromosphere unable to radiate energy deposited by non-thermal electrons • Velocities > 400 km/s • Flux > 1010 ergs cm-2 s-1 • Gentle • Chromosphere heated directly by non-thermal electrons • Velocities < 300 km/s • Flux < 1010 ergs cm-2 s-1 Threshold? v/2.35cs Gentle Explosive Log F (ergs s-1 cm-2) Peter Gallagher (UCD)

  5. 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)

  6. Footpoint Downflows • Loops are not static • Maximum downflow ~110 km/sec • Loops cool via conduction, radiation, and flows. (SHOW MOVIE) Peter Gallagher (UCD)

  7. RHESSI Integrated Spectrum Peter Gallagher (UCD)

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

  9. 6 - 12 keV (dashed line) Thermal 25 – 50 keV (solid line) Non-thermal Peter Gallagher (UCD)

  10. RHESSI Lightcurve Peter Gallagher (UCD)

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

  12. 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 = 260 km s-1 Peter Gallagher (UCD)

  13. Flow velocity vs. Temperature Downflows Upflows Peter Gallagher (UCD)

  14. In context … M2.2 flare Peter Gallagher (UCD)

  15. Future Work • How does the chromospheric response depend on the nonthermal electron properties? • We now have one event! • Nonthermal electrons: ~7.3, Ec~ 24 keV, F~2x1010 ergs cm-2 s-1 • Response: ~260 km s-1 • => need large number of CDS/RHESSI flares • Is there a threshold for explosive evaporation? • => need large number of CDS/RHESSI flares Peter Gallagher (UCD)

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