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Modern Solar Facilities – Advanced Solar Science, 277–280 F. Kneer, K. G. Puschmann, A. D. Wittmann (eds.) c  Universitätsverlag Göttingen 2007 On the thermal and non-thermal excitation effects as studied in the Hα, Hβ and Ca II 8542 Å line profiles in a solar flare P. Kotrč1,* and L. K. Kashapova2 1 Astronomical Institute AS CR, Ondřejov, Czech Republic 2 Institute of Solar-Terrestrial Physics, Irkutsk, Russia * Email: pkotrc@asu.cas.cz Abstract. Spectral observations of the 26 June 1999 flare (Kotrč et al. 2004) presented a unique opportunity to compare effects of thermal and non-thermal mechanisms of excitation on profiles of Balmer series and Ca ii 8542 Å lines. The radio spectra and HXR flux demonstrated indirect evidence of the non-thermal beam effect on the chromosphere during the flare (Kashapova et al. 2005). We compared the line profiles in the flare kernel associated with the influence of non-thermal electron beams with the ”only thermal” kernels. Results are discussed both from their observational and theoretical aspects. 1 Introduction Nowadays it is accepted that the solar flare energy is initially released in the corona and then transported by various means from the primary release site to chromosphere. The high-energy particle beams are the fastest and effective transportation agents. This type of emission excitation is called non-thermal. However, diagnostics of the lower atmosphere response to the particle beams still remains an unsolved problem of solar flare physics. Many of the investigators (Fang et al. 2004; Heinzel 2003) considered the hydrogen and Ca lines as dominating diagnostic tools to study the energy mechanisms in the solar atmosphere. However, the obtained results are not based on any well-defined method. Thus, simultaneous observations in Hα and in Ca ii 8542 Å revealed the fact of opposite asymmetries at the same moments of the flare (Mein et al. 1997). The theoretical simulations (Ding & Fang 1996) showed that under downwards motion the Hα line profiles will be sensitive to the location of the moving region (from top to deeper layers) while the Ca ii K line will not. The deeper the moving region the more significant was the effect. The solar flare on 26 June 1999 consisted of three phases. The fact that we found an indirect evidence of accelerated non-thermal particle beams for only the second phase of the flare, allowed us to distinguish the emission kernels according to mechanisms of excitation and compare the characteristics of profiles of the Balmer and Ca ii 8542 Å lines observed by the Ondřejov Multichannel Flare Spectrograph, hereafter MFS. 278 P. Kotrč and L. Kashapova: On the thermal and non-thermal excitation effects in flares Figure 1. Position of HXR source obtained by Yohkoh Hard X-ray Telescope (from 07:17:12.214 to 07:17:39.714 UT) and the Hα slit-jaw image of the flare taken at 07:23:18 UT (shaded area) as projected on images in the 1600 Å band at 07:17:15 UT and 07:28:45 UT (from left to right). The L band (13.9 - 22.7 keV) and the M1 band (22.7 - 32.7 keV) are marked by dashed and full lines, respectively. Figure 2. Top: Composed Hβ line spectrogram, Hα slit-jaw filtergram, Hα line and Ca ii 8542 Å line spectrograms (from left to right) taken by MFS at 07:08:53 UT (the first phase of the flare - thermal). Bottom: Hα, Hβ and Ca ii 8542 Å intensity profiles. The type of line corresponds to the scan position as marked on the top panel. The solid and dashed lines are the quiet region and tabulated profiles, correspondingly. 2 Effect of non-thermal electrons: discussion and preliminary conclusions As can be seen in Figure 1 at the 1600 Å image the emission kernels associated with the HXR source were compact and bright at 07:17:15 UT (the moment of HXR flux rising). But at 07:28:45 UT the intensity of the kernel decreased and the structure became diffuse. We can see only one bright point in this kernel. Possibly, this point corresponds to the real location P. Kotrč and L. Kashapova: On the thermal and non-thermal excitation effects in flares 279 Figure 3. The same as in Figure 2 at 07:40:37 UT (the third phase of the flare - thermal again). Figure 4. The same as in Figure 2 at 07:23:42 UT (the second flare phase - non thermal). of...

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