september 21, 2005peter gallagher (ucd) chromospheric evaporation peter gallagher university college...
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September 21, 2005 Peter Gallagher (UCD)
Chromospheric EvaporationChromospheric Evaporation
Peter GallagherUniversity College Dublin
Ryan MilliganQueen’s University Belfast
September 21, 2005 Peter Gallagher (UCD)
September 21, 2005 Peter Gallagher (UCD)
Canonical Flare ModelCanonical Flare Model
o Step 1: Acceleration.o Reconnection produces power-law
electron distribution.
o Step 2: Propagation.o Electrons spiral along magnetic fields
from corona to chromosphere.
o Step 3: Heating.o Electrons deposit energy in chromosphere
via Coulomb collisions.
o Step 4: Evaporation.o Dense chromosphere radiates and may
expand.
September 21, 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- electrons cm-2 s-1
T1: NonthermalElectrons
T2: Impulsive Heating
T3: VUP
T3: VDOWN
Density
Loop leg
September 21, 2005 Peter Gallagher (UCD)
Chromospheric ResponseChromospheric Response
o Chromospheric response depends on properties of accelerated electrons:
o Low-energy cut-off (Ec)o Lower Ec => more energy => more rapid and
pronounced response.
o Power-law index ()o Harder spectrum => high energy electrons
penetrate deeper where chromospere better able to radiate => less rapid and pronounced response.
o Total fluxo Higher flux => more energy => more rapid and
pronounced response.
EC
E
f(E)
nonthermalthermal
€
P = f (E)dEEc
∞
∫
September 21, 2005 Peter Gallagher (UCD)
Gentle Explosive
Flux (ergs cm-2 s-1) <1010 >3 x 1010
T (K) <106 >107
P (dyn cm-2) x10 x100-1000
Upflows (km s-1) 10’s 100’s
Downflows (km s-1) 0 10’s
Gentle vs Explosive EvaporationGentle vs Explosive Evaporation
September 21, 2005 Peter Gallagher (UCD)
Gentle vs Explosive EvaporationGentle vs Explosive Evaporation
QuickTime™ and aTIFF (Uncompressed) decompressor
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September 21, 2005 Peter Gallagher (UCD)
September 21, 2005 Peter Gallagher (UCD)
September 21, 2005 Peter Gallagher (UCD)
RHESSI Spectral CoverageRHESSI Spectral Coverage
September 21, 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)
September 21, 2005 Peter Gallagher (UCD)
RHESSI Integrated SpectrumRHESSI Integrated Spectrum
September 21, 2005 Peter Gallagher (UCD)
Footpoint DownflowsFootpoint Downflows
o Loops are not static.
o Downflows <50 km s-1, upflows >100 km s-1
o Loops cool via conduction, radiation, and flows.
September 21, 2005 Peter Gallagher (UCD)
M2.2 Flare – CDS/EIT/GOESM2.2 Flare – CDS/EIT/GOES
September 21, 2005 Peter Gallagher (UCD)
M2.2 Flare – CDS/EIT/GOESM2.2 Flare – CDS/EIT/GOES
September 21, 2005 Peter Gallagher (UCD)
RHESSI LightcurveRHESSI Lightcurve
September 21, 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 >3x1010 ergs cm-2 s-1
September 21, 2005 Peter Gallagher (UCD)
6 - 12 keV (dashed line)
Thermal
25 – 50 keV (solid line)
Non-thermal
September 21, 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 = 270 km s-1
September 21, 2005 Peter Gallagher (UCD)
Flow velocity vs. TemperatureFlow velocity vs. Temperature
September 21, 2005 Peter Gallagher (UCD)
Future WorkFuture Work
o How does the chromospheric response depend on the nonthermal electron properties?
o We only have one event!o Nonthermal electrons => F>3x1010 ergs cm-2 s-1
o Response => ~ -30 km s-1 and 270 km s-1
o Is there a threshold for explosive evaporation? Heating < expansion => 3kT / Q < L/cs
o => need large number of CDS/RHESSI flares