NNON-THERMALON-THERMAL DISTRIBDISTRIBUTIONS UTIONS

AND THE CORONAL EMISSIONAND THE CORONAL EMISSION

J. Dudík J. Dudík 11, A. Kulinov, A. Kulinová á 1,21,2,,EE.. Dzif Dzifčáková čáková 1,21,2, M. Karlický , M. Karlický 22

11 – OAA KAFZM FMFI – OAA KAFZM FMFI, , Univerzita Komenského, BratislavaUniverzita Komenského, Bratislava22 – Astronomický Ústav Akademie Věd ČR, v.v.i., Ondřejov – Astronomický Ústav Akademie Věd ČR, v.v.i., Ondřejov

Zářivě MHD Seminář, ASÚ AVČR Ondřejov, 28. 05. 2009Zářivě MHD Seminář, ASÚ AVČR Ondřejov, 28. 05. 2009

OutlineI. Solar corona, coronal loops and the coronal heating problem

Temperature, density and spatial structure of the coronaFIP effect, Coronal heating problem

II. –distributionsWhy –distributions?Definition and basic propertiesIonization and excitation equilibrium

III. TRACE EUV filter responsesDefinition and constructionSynthetic spectrum for the –distributionsContinuum and the missing linesResponse as function of temperature and electron densityTemperature diagnostic from observationsFuture work

Solar corona Highest “layer” of the Sun’s atmosphere

Highly structured: – in white-light: coronal streamers (radial and helmet)– in EUV and X-rays: coronal loops, coronal holes, brightenings (open and closed structures)

I.

Solar corona - properties Hot and tenuous plasma (Edlén, 1943)

Tcor 106 – 107 K ne,cor 108 – 1010 cm–3

highly ionized, frozen-in approximation optically thin (collisional excitation, spontaneous emission) Anisotropy – multitemperature corona

171 (1 MK)195 (1.5 MK)284 (2 MK)

Coronal EUV emission Emissivity ij of a spectral line line – transition from the level i to level j

in a k-times ionized element x is given by:

Coronal abundances of elements with lower first ionization potential lower than 10 eV are significantly higher than photospheric abundances – FIP effect

2He

e e

2, e e( , , , , )

kij i

ij ij i xk xij ij

x ij x ij

A n nhc hc nA n A n

n nn n

G T n A n

Coronal heating problem

Corona is ~ 100-times hotter than the upper chromosphere, and is significantly less dense

In the absence of an energy source, the corona would cool down during ~ 101 hours due to the radiative losses

Coronal heating problem

(might be a paradoxical misnomer: chromospheric heating & coronal loops filling problem)

The only way to identify the heating mechanism is to study the coronal emission

distributions: whyII. Study the emission = need to know the microphysics Suprathermal component (“high-energy tail”) present during flares and

also in solar wind Some emission line ratios are not consistent with the assumption of

Maxwellian (thermal) distribution Owocki & Scudder (1983): two-parametric distribution characterized by

parameters and T, enables to explain the observed O VII / O VIII line ratios

Maksimovic et al. (1997): solar wind velocity distribution is better approximated by one distribution than with one or sum of two Maxwellians

Collier (2004): if the mean particle energy is not held constant, the entropy is not maximalized by a Maxwellian distribution.

If the order of the mean energy conserved is, entropy is maximalized by the distribution

distributions: definition

B

1/ 2

3/ 2 1B

( 3 / 2)

1( , )

1E

k T

E dEE dE A

k T

F

Owocki & Scudder (1983), Dzifčáková (2006a):

Maxwellian distribution

B3

2E k T

B1 3/ 2

2 1/ 2pE k T

Fe Ionization equilibriumDzifčáková (2002): Changes in the Fe IX – XVI ionization equilibrium for the distributions with respect to Maxwellian one are significant:

Fe XV excitation equilibriumDzifčáková (2006a): Changes in the exictation equilibrium for distributions with respect to Maxwellian one are dependent on the collisional cross-section, type of transition and the energy of the transition

Synthetic spectra CHIANTI (Dere a kol., 1997; Landi a kol., 2006) version 5.2 – free

atomic database and software for computation of synthetic spectra in UV and X-ray spectral domain

Dzifčáková (2006b; 2009, in preparation): Modification of the CHIANTI database and software to compute the synthetic spectra for the non-thermal distributions

Ionization equilibrium only for C, N, O, Ne, Mg, Al, Si, S, Ar, Ca, Fe, Ni

No continuum

Should be available in the next version of CHIANTI

Filter response to emission

2e e e( , , ) ( ) ( , , , )F T n f G T n d n dl

optically thin environment – integral along the line-of-sight lf () – filter + instrument transmssivity (instrumental spectral response)

G(,T,ne,) – contribution function

log10(EM) = 27 [cm–5]

You can compute F with SolarSoft, but many people:

Use wrong abundances (photospherical, not coronal)

Assume of constant pressure, not separate dependence on T and ne

Maxwellian distribution (always)!

Continuum + missing ions

Dudík a kol. (2009, subm. to A&A) He II 304 Ǻ, log10(T) ~ 4,9

Maxwell distribution only

F(T, ne ,) : Width

Width of a function? Two ways to define:

FWHM - Full Width at Half–Maximum

– find Fmax a Tmax

– find Fmax/2 and corresponding T1, T2; FWHM = T2 – T1

Equivalent width W: Area divided by the maximum value

10

10

log ( ) 8,0

e e 10max e log ( ) 4,5

1( , ) ( , , ) ln(10) log ( )

( , )

T

T

W n F T n T d TF n

F(T, ne ,): Width, Tmax shift

Dependence on ne

Temperature diagnostic

Future work

XRT (X-rays): higher temperature span, unambiguous determination of T by the CIFR method (Reale et al., 2007)

Continuum important in X-ray spectral domain

There are no works dealing on the X-ray continuum for non-thermal distributions

If its not important, we’ll try to do the XRT filter responses

Summary

Conditions in solar corona allow for non-thermal distributions. distribution is a likely candidate

Emission is the only way to study the environment: careful analysis is needed if the coronal heating problem is to be constrained

Filter responses are strongly dependent on the assumed distribution: wider range of observed T !