N ON-THERMAL k - DISTRIB UTIONS AND THE CORONAL EMISSION

1. NON-THERMALk-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, 28. 05. 2009

3. 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. k–distributions Why k–distributions? Definition and basic properties Ionization and excitation equilibrium III. TRACE EUV filter responses Definition and construction Synthetic spectrum for the k–distributions Continuum and the missing lines Response as function of temperature and electron density Temperature diagnostic from observations Future work

4. Solar corona I. Highest “layer” of the Sun’s atmosphere • Highly structured: – in white-light: coronal streamers (radial and helmet) – in EUV andX-rays: coronal loops, coronal holes, brightenings (open and closed structures)

5. Solar corona - properties Hot and tenuous plasma (Edlén, 1943) Tcor 106 –107 K ne,cor 108 – 1010cm–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)

6. Coronal EUV emission Emissivityeijof a spectral line line – transition from the level ito leveljin ak-times ionizedelement x is given by: Coronal abundances of elements with lower first ionization potential lower than 10 eV are significantly higher than photospheric abundances – FIPeffect

7. 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

8. k-distributions: why II. 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 kandT, enables to explain the observed O VII / O VIII line ratios Maksimovic et al. (1997): solar wind velocity distribution is better approximated by one k-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 thek-distribution

9. k-distributions: definition Owocki & Scudder (1983), Dzifčáková (2006a): k   Maxwellian distribution

10. Fe Ionization equilibrium Dzifčáková (2002): Changes in the Fe IX – XVI ionization equilibrium for the k-distributionswith respect to Maxwellian one are significant:

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

12. 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

13. Filter response to emission optically thin environment – integral along the line-of-sight l f (l) –filter + instrument transmssivity (instrumental spectral response) G(l,T,ne,k) – contribution function log10(EM) = 27 [cm–5] You can compute Fwith SolarSoft, but many people: Use wrong abundances (photospherical, not coronal) Assume of constant pressure, not separate dependence onTandne Maxwellian distribution (always)!

14. Continuum + missing ions Maxwell distribution only He II 304 Ǻ, log10(T) ~4,9 Dudík a kol. (2009, subm. to A&A)

16. F(T, ne,k) :Width Width of a function? Two ways to define: FWHM - Full Width at Half–Maximum – findFmax a Tmax – findFmax/2and corresponding T1,T2; FWHM = T2 – T1 Equivalent widthW: Area divided by the maximum value

17. F(T, ne,k): Width, Tmax shift

18. Dependence on ne

19. Temperature diagnostic

21. 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

22. Summary Conditions in solar corona allow for non-thermal distributions. k-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!

23. Thank you for your attention