Chromospheric Evaporation
Peter Gallagher
University College Dublin
Ryan Milligan
Queens University Belfast
Locarno, 8 June 2005
Peter Gallagher (UCD)
Chromospheric 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 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
T1: Nonthermal
Electrons
Loop leg
o Chromospheric response depends on
properties of accelerated electrons:
T3: Vup<1000 km/s
1. Low-energy cut-off (Ec).
2. Power-law index ().
T2: Impulsive Heating
3. Total flux.
Density
T3: VDOWN<100 km/s
Locarno, 8 June 2005
Peter Gallagher (UCD)
o Explosive
o Gentle
o Chromosphere heated directly by
non-thermal electrons
o Velocities < 300 km/s
o Flux < 1010 ergs cm-2 s-1
o Chromosphere unable to radiate
energy deposited by non-thermal
electrons
o Velocities > 400 km/s
o Flux > 1010 ergs cm-2 s-1
v/2.35cs
Threshold?
Gentle
Explosive
Locarno, 8 June 2005
Log F (ergs s-1 cm-2)
Peter Gallagher (UCD)
CDS and TRACE: 26 March 2002 Flare
o
SOHO/CDS
o
o
o
o
o
He I (0.03 MK)
O V (0.25 MK)
Mg X (1.1 MK)
Fe XVI (2.5 MK)
Fe XIX (8 MK)
o TRACE 17.1 nm
o Fe IX/X (1.0 MK)
Locarno, 8 June 2005
Peter Gallagher (UCD)
Footpoint Downflows
o Loops are not static
o Maximum downflow ~110 km/sec
o Loops cool via conduction, radiation, and flows. (SHOW MOVIE)
Locarno, 8 June 2005
Peter Gallagher (UCD)
RHESSI Integrated Spectrum
Locarno, 8 June 2005
Peter Gallagher (UCD)
M2.2 Flare – CDS/EIT/GOES
Locarno, 8 June 2005
Peter Gallagher (UCD)
6 - 12 keV (dashed line)
25 – 50 keV (solid line)
Thermal
Non-thermal
Locarno, 8 June 2005
Peter Gallagher (UCD)
RHESSI Lightcurve
Locarno, 8 June 2005
Peter Gallagher (UCD)
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
Locarno, 8 June 2005
Peter Gallagher (UCD)
Evidence for Upflows
Doppler shifts
measured relative to
a stationary
component:
Blueshifted
Fe XIX
Component
Stationary Fe XIX
Component
v/c = (-  0)/  0
In Fe XIX
v = 260 km s-1
Locarno, 8 June 2005
Peter Gallagher (UCD)
Flow velocity vs. Temperature
Downflows
Upflows
Locarno, 8 June 2005
Peter Gallagher (UCD)
In context …
M2.2 flare
Locarno, 8 June 2005
Peter Gallagher (UCD)
Future 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
Locarno, 8 June 2005
Peter Gallagher (UCD)

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