Locarno, 8 June 2005 Peter Gallagher (UCD)

Chromospheric EvaporationChromospheric Evaporation

Peter GallagherUniversity College Dublin

Ryan MilliganQueens University Belfast

Locarno, 8 June 2005 Peter Gallagher (UCD)

Chromospheric EvaporationChromospheric Evaporation

o Non-thermal electrons supply the necessary energy to heat the plasma and cause flows.Enonthermal -> Ethermal + Ekinetic

Locarno, 8 June 2005 Peter Gallagher (UCD)

Chromospheric ResponseChromospheric Response

o How does the chromosphere respond to nonthermal electrons?

o Assume power-law electron spectrum:o F(E) ~ (E/Ec)- electrons cm-2 s-1

o Chromospheric response depends on properties of accelerated electrons:1. Low-energy cut-off (Ec).2. Power-law index ().3. Total flux.

T1: NonthermalElectrons

T2: Impulsive Heating

T3: Vup<1000 km/s

T3: VDOWN<100 km/s

Density

Loop leg

Locarno, 8 June 2005 Peter Gallagher (UCD)

o Gentleo Chromosphere heated directly by

non-thermal electronso Velocities < 300 km/so Flux < 1010 ergs cm-2 s-1

o Explosiveo Chromosphere unable to radiate

energy deposited by non-thermal electrons

o Velocities > 400 km/so Flux > 1010 ergs cm-2 s-1

Gentle

Explosive

Threshold?

v/2.

35c s

Log F (ergs s-1 cm-2)

Locarno, 8 June 2005 Peter Gallagher (UCD)

CDS and TRACE: 26 March 2002 FlareCDS and TRACE: 26 March 2002 Flare

o SOHO/CDSo He I (0.03 MK)o O V (0.25 MK)o Mg X (1.1 MK)o Fe XVI (2.5 MK)o Fe XIX (8 MK)

o TRACE 17.1 nmo Fe IX/X (1.0 MK)

Locarno, 8 June 2005 Peter Gallagher (UCD)

Footpoint DownflowsFootpoint Downflows

o Loops are not statico Maximum downflow ~110 km/seco Loops cool via conduction, radiation, and flows. (SHOW MOVIE)

Locarno, 8 June 2005 Peter Gallagher (UCD)

RHESSI Integrated SpectrumRHESSI Integrated Spectrum

Locarno, 8 June 2005 Peter Gallagher (UCD)

M2.2 Flare – CDS/EIT/GOESM2.2 Flare – CDS/EIT/GOES

Locarno, 8 June 2005 Peter Gallagher (UCD)

6 - 12 keV (dashed line)

Thermal

25 – 50 keV (solid line)

Non-thermal

Locarno, 8 June 2005 Peter Gallagher (UCD)

RHESSI LightcurveRHESSI Lightcurve

Locarno, 8 June 2005 Peter Gallagher (UCD)

RHESSI SpectrumRHESSI 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

Locarno, 8 June 2005 Peter Gallagher (UCD)

Evidence for UpflowsEvidence for Upflows

Stationary Fe XIX Component

Blueshifted Fe XIX Component

Doppler shifts measured relative to a stationary component:

v/c = (- 0)/ 0

In Fe XIX

v = 260 km s-1

Locarno, 8 June 2005 Peter Gallagher (UCD)

Flow velocity vs. TemperatureFlow velocity vs. Temperature

Downflows

Upflows

Locarno, 8 June 2005 Peter Gallagher (UCD)

M2.2 flare

In context …

Locarno, 8 June 2005 Peter Gallagher (UCD)

Future WorkFuture Work

o How does the chromospheric response depend on the nonthermal electron properties?

o We now have one event!o Nonthermal electrons: ~7.3, Ec~ 24 keV, F~2x1010 ergs cm-2 s-1

o Response: ~260 km s-1

o => need large number of CDS/RHESSI flares

o Is there a threshold for explosive evaporation?o => need large number of CDS/RHESSI flares