impact of nonthermal tails and nonthermal distributions on solar flare plasma diagnostics

Jaroslav Dudík 1,2, Elena Dzifčáková 2, Michal Homola 1, Marian Karlický 2, Alena Kulinová 1,2, Jana Kašparová 2

1 – DAPEM, Faculty of Mathematics, Physics and Informatics,Comenius University, Bratislava, Slovakia

2 - Astronomical Institute of the Academy of SciencesOndřejov, Czech Republic

„From Atoms to Stars: The Impact of Spectroscopy on Astrophysics“, Celebrating the Career of Prof. Carole Jordan, Oxford, UK, July 27, 2011

Impact of nonthermal tailsand nonthermal distributions

on flare plasma diagnostics

Outline

I. The power-law distributions (nonthermal tails)Motivation: RHESSI flare observations

II. The n-distributionsDefinition and properties Seely et al. (1987)

Diagnostics from observations Dzifčáková et al. (2008)

Kulinová et al. (2011)

Physical background Karlický et al. (2011), in prep.

The nonthermal continuum Dudík et al. (2011), in prep.

III. The composed np-distributions Dzifčáková et al. (2011)

Construction: „know how“Effect on ionization equilibrium and line intensitiesFlare plasma diagnostics

I. The nonthermal tails

Veronig et al. (2010), ApJ 719, 655

The nonthermal tails

Gabriel & Phillips (1979),

MNRAS 189, 319:

Effect on the Fe XXIVd / Fe XXV

satellite/allowed line ratios

- excess excitation of the Fe XXV line

- decrease of the ratio by up to 40%

However, an increase is observed

(even with respect to Maxwellian):

Seely, Feldman & Doschek (1987),

ApJ, 319, 541

II. The n-distributions

B

11/2 2

ε/

3/2BB

2ε ε(ε) ε e ε

n

k Tn nf d B d

k Tk T

Peak narrower than MaxwellianVery few low-energy electrons

Pseudo-temperature t :

Seely, Feldman & Doschek (1987),ApJ 319, 541Dzifčáková (1998), SoPh 187, 317

t

31

2 2

nE k kT

The n-distributions

Changes in ionization and excitation equilibrium – line intensities

Contribution functions - narrower and shifted to different t

Dzifčáková & Tóthová (2007), SoPh 240, 211; Dudík et al. (2011), AA 529, A103

Diagnostics from observations

Dzifčáková et al. (2008), AA 488, 311

Kulinová et al. (2011), AA, accepted

Observed spectra - RESIK

Diagnostics - results

Theoretical f-b continuum

Dudík et al. (2011), in prep.

Physical background - drifts

Karlický, Dzifčáková & Dudík (2011), in prep.:

„Moving Maxwell“ (Maxwellian with a drift velocity v0)

can be written as

With the f(E,v0) having the same gradient as the n-distribution.

Physical background - drifts

Diagnostics - RHESSI

Kulinová et al. (2011), AA, accepted

Diagnostics - RHESSI

III. The composed np-distributions

Dzifčáková, Homola & Dudík (2011), AA 531, A111:

Composed np-distribution: Bulk (n) + Tail (p)

n – index n describing the bulkp – power-law index of the high-energy tailEC – low-energy cutoff for the power-law taila/b – bulk/tail ratio, a + b = 1

Construction of the distribution

Conditions for EC :

- the power-law tail does not affect the plasma bulk

- less than 10% discontinuity at EC

Construction of the distribution

Ionization equilibrium – tail only

Ionization equilibrium – bulk + tail

Si XIId, XIII, XIV flare spectra

Conclusions

High-energy tail can change the ionization equilibrium

Changes the temperature diagnostics from ratios of allowed lines

Nonthermal bulk necessary to explain the Si XIId / Si XIII ratios

- has a physical explanation – drift velocities (return current)

- can also be diagnosed from RHESSI at < 6 keV

Composed distributions offer simple parametrization

of the true electron energy distributions in flares

Easy calculation of spectra using modified CHIANTI

Thank you for your attention