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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 !