NON-THERMAL   DISTRIBUTIONS AND THE CORONAL EMISSION J. Dudík 1, A. Kulinová 1,2, E. Dzifčáková 1,2, M. Karlický 2 1 – OAA KAFZM FMFI, Univerzita Komenského, Bratislava 2 – Astronomický Ústav Akademie Věd ČR, v.v.i., Ondřejov Zářivě MHD Seminář, ASÚ AVČR Ondřejov,

Outline I.Solar corona, coronal loops and the coronal heating problem Temperature, density and spatial structure of the corona FIP effect, Coronal heating problem II.  –distributions Why  –distributions? Definition and basic properties Ionization and excitation equilibrium III.TRACE EUV filter responses Definition and construction Synthetic spectrum for the  –distributions Continuum and the missing lines Response as function of temperature and electron density Temperature diagnostic from observations Future 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) T cor  10 6 – 10 7 Kn e,cor  10 8 – 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

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 ~ 10 1 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 Owocki & Scudder (1983), Dzifčáková (2006a):   Maxwellian distribution  

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

Fe XV excitation equilibrium Dzifčáková (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  optically thin environment – integral along the line-of-sight l  f ( ) – filter + instrument transmssivity (instrumental spectral response)  G(,T,n e,  ) – contribution function  log 10 (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 n e  Maxwellian distribution (always)!

Continuum + missing ions Dudík a kol. (2009, subm. to A&A) He II 304 Ǻ, log 10 (T) ~ 4,9 Maxwell distribution only

F(T, n e,  ) : Width Width of a function? Two ways to define:  FWHM - Full Width at Half–Maximum – find F max a T max – find F max /2 and corresponding T 1, T 2 ; FWHM = T 2 – T 1  Equivalent width W : Area divided by the maximum value

F(T, n e,  ) : Width, T max shift

Dependence on n e

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 !