Preliminary Results of Optical Solar Flare Spectra Studies Using a 40-Channel Densitometer

Abstract

Multi-channel CCD receivers are available for solar spectral research in the Astronomical Observatory of Shevchenko University of Kiev. The observational material considered here are 24 echelle spectrograms of the flare of July 15, 1981 and certain other disk and limb flares. Some temporal aspects of flare development are discussed, as well as properties of metal lines and the structure of the flare region. Disk and limb flare photometry indicate the full spatial coincidence of the emission volumes for all emission lines. No signs of altitude stratification for the lines of H and K Call, hydrogen, and other metals are detected. Metal flare emission is revealed in the cores of Fraunhofer lines, providing that a compact emission source is present in the active region and that broad wings of H and K CaII and hydrogen have formed. No broad wings are observed for metal lines. Two types of lower-intensity strips in the photospheric emission spectrum are detected; the first is the result of the lower temperature in sunspots, while the second is due to the weakening of photospheric radiation after it passes through the flare volume. No new spectral lines are observed in the spectrum of this second type of strip, which may be associated with a condensed layer of relatively cold plasma at the chromospheric level. Four components are always spatially coincident in the spectrum: (1) a compact source of higher intensity with broadened hydrogen and H and K Call line wings; (2) higher intensity in metal lines, but without broadened wings; (3) emission or absorption in helium lines; (4) a lower-intensity strip of photospheric emission due to its weakening after it passes through the flare volume.