 |
Akademie věd České republiky |
 |
|
Akademie věd České republiky |
|
Pravidelný seminář 19. 6. 2006
|
který se koná v pondělí dne v zasedací místnosti Kosmické laboratoře AsÚ v Ondřejově PROGRAM: 13:00 odborná část V odborné části vyslechneme informace ze slunečního oddělení: Diagnostics of the EUV
filaments using the non-LTE modelling of profiles of the hydrogen
spectral lines
Pavol Schwartz It was found recently (Heinzel et al. 2001; Schmieder et al. 2003, 2004) that filaments are more extended when observed in EUV spectral lines with wavelengths below the hydrogen Lyman continuum head (912 A) than in the H_alpha line. These extended dark structures visible in EUV are called EUV filaments. EUV filaments consist of very dark parts which are co-spatial with the H_alpha filament (i.e. H_alpha filaments) and of less dark so-called EUV extension. In the H_alpha filament all EUV radiation with wavelength below 912 A is absorbed. The EUV extensions are visible in H_alpha only faintly or even not visible at all due to low contrast - the optical thickness is lower than 1 in the center of the H_alpha line. Howerver, the optical thickness of the Lyman continuum can produce, for the same column density, a well observable contrast. The intensity depression of the EUV lines is caused by two processes: absorption and volume blocking. These both processes can contribute together to the intensity depression. The first mechanism concerns the absorption in the hydrogen Lyman continuum within the cool filament plasma of the EUV-line radiation emitted from beneath the filament. Then only the radiation with wavelength below 912 A emitted from corona or transition region is affected. The second mechanism – volume blocking – can influence only intensities of coronal lines (assuming that the EUV filament is situated in the heights above the transition region). This mechanism is based on the fact that hot coronal lines cannot be emitted from the volume occupied by cool filament plasma. To study the nature of the EUV extensions and the relative contributions of the absorption and volume blocking to the intensity depression we fitted hydrogen spectral lines with synthetic ones computed using a non-LTE one-dimensional slab model. We found that absorption dominates only in the H_alpha filament. In the vertically large EUV extension the volume blocking is important process throughout whole this structure. Srdečně zve Vladimír Karas vedoucí semináře |