Spectral analysis of sunspot flares

Abstract

We have qualitatively analyzed, in the H and K lines spectral region, 31 flares covering part of umbrae or penumbrae of sunspots. A strong narrowing of the emission lines has been observed over the umbrae, and the lines are, in general, much weaker than in common flares suggesting that the optical thickness is quite low in these parts. We have calculated the Stark broadening of the He line from the general theory, and it has been applied to obtain the electron density in 9 flare spectra. In all cases it has been found that n~> 1013 cm -3. Goldberg's method has been applied to find the kinetic temperature from the H and K lines of Ca II, and from the ratio between the central intensities of the lines we have calculated the optical thickness in the K line. Much evidence supports the assumption that the flare emission is highly diluted* * in the cases considered, and we propose a two-component model for the calcium emission lines.

Analysis of the August 7, 1972 white light flare: Its spectrum and vertical structure

“…We next plotted the classification given to the iron lines against the excitation potential of the line itself as in a previous paper (Machado, 1971). We found the same kind of relation as in the March 12, 1969 flare; that is, the lines of high excitation potential are less affected than those of low excitation potential.…”

“…In this way we may determine whether lines formed deeper in the atmosphere are more affected in the continuum emission region, and we may also infer an approximate depth of penetration of the flare. We used the same classification scheme as Machado (1971):…”

“…Lacking evidence to the contrary, we suggest, therefore, that that is probably the normal behavior in white light flares. Machado (1971) took the correspondence between the classification given to the Fe I lines with their excitation potentials as evidence of flare penetration to deep layers of the solar atmosphere and of the probable photospheric origin of the continuum. We now have estimates of the depth of formation of several iron lines.…”

“…We subtracted the background spectrum from the flare emission line spectrum in the same way as described by several authors (e.g. Svestka, 1965 and references therein, and Machado and Seibold, 1973). The only difference is that in our case we also had to subtract the continuous emission produced by the flare itself.…”

“…Ellison was the first to observe the spectrum of the continuous emission. Recently, another white light flare spectrum was obtained by Grossi et al (1971), and Machado (1971) showed that the continuum probably originated deep in the atmosphere. Svestka (1970), Najita and Orrall (1970) and Hudson (1972) have proposed that the white light emission originates in photospheric layers overheated by accelerated particles precipitating from the corona (Svestka, and Najita and Orrall), or by free-bound emission of hydrogen atoms at higher levels in the atmosphere (Hudson).…”