RELATION BETWEEN COOL AND HOT POST-FLARE LOOPS OF 26 JUNE 1992 DERIVED FROM OPTICAL AND X-RAY (SXT-YOHKOH) OBSERVATIONS

We have analyzed the physical conditions of the plasma in post-flare l oops with special emphasis on dynamics and energy transport using SXT- data (hot plasma) and optical ground-based data from Pic du Midi, Wroc law, and Ondrejov (cool plasma). By combining the H alpha observations with the SXT images we can understand the relationship between cool a nd hot plasmas, the process of cooling post-flare loops and the mechan ism which maintains the long duration of these loops. Using recent res ults of NLTE modeling of prominence-like plasmas, we derive the emissi on measure of cool H alpha loops and this gives us a realistic estimat e of the electron density (2.2 x 10(10) cm(-3)). Then, by comparing th is emission measure with that of hot loops derived from SXT data, we a re able to estimate the ratio between electron densities in hot and co ol loops taking into account the effect of geometrical filling factors . This leads to the electron density in hot loops 7 x 10(9) cm(-3). We also derive the temperature of hot X-ray loops (similar or equal to 5 .5 x 10(6) K), which, together with the electron density, provides the initial values for solving the time-dependent energy balance equation . We obtain the cooling times which are compared to a typical growth-t ime of the whole loop system (similar to 2000 s). In the legs of cool H alpha loops, we observe an excess of the emission measure which we a ttribute to the effect of Doppler brightening (due to large downflow v elocities).