Post on 12-Jan-2016
Locarno, 8 June 2005 Peter Gallagher (UCD)
Chromospheric EvaporationChromospheric Evaporation
Peter Gallagher
University College Dublin
Ryan Milligan
Queens 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 electrons
o Velocities < 300 km/s
o 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 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 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