Investigation of the Mg XII 8.42 � doublet in solar flare spectra

Abstract

The intensity ratio of the components of the Mg xn 8.42 ~ (ls 2S1/2 -2p 2P1/2. 3/2) doublet in solar flare spectra has been investigated using observations recorded from the Intercosmos 7 satellite. The observed values of the ratio fall within the interval 0.38-0.66 and have been compared with recent theoretical predictions based on an optically thin collisional-radiative model. It has been found that for the flare plasma the low values of the ratio cannot be explained since they fall below the smallest theoretical value. The highest values on the other hand require that an unacceptably high electron density be postulated. It is suggested that both high and low values may be caused by the resonance line scattering of the Mg xH quanta in the flare volume, provided that the volume is elongated and not spherical.The intensity of the nearby satellite lines is also investigated. Good agreement between the theoretical and observed intensities is found.

A further investigation of the Mg xii 8.42 � doublet in a solar flare spectrum

“…The results of this study confirm the previous results of Sylwester et al (1986) and show that there is a persistent tendency for the intensity ratio between the components of the Mgxn doublet at 8.42 ~ to exceed 0.5, the value predicted theoretically. This is shown most clearly in the histograms of Figure 3.…”

“…This is shown most clearly in the histograms of Figure 3. The explanation for these results is probably non-negligible opacity in a non-spherical source, as suggested by Sylwester et aL (1986). Because the opacity is non-zero, radiation is more likely to escape from the source in the direction along its shortest dimension, and less likely along its greatest dimension.…”

“…The explanation for these results is probably non-negligible opacity in a non-spherical source, as suggested by Sylwester et aL (1986). This possibility is discussed by Sylwester et al (1986). This effect will be more evident in stronger lines, so that B will be larger than its predicted value.…”

“…In a recent paper Sylwester et al (1986)reported an analysis of some early observations of the intensity ratio of the components of the L e ( 1S -2P) transition in Mg xII at 8.419 and 8.425 A. They found that the value of the ratio (for which they used the symbol B) was significantly different from the value of less than 0.515 predicted by theory and suggested an explanation in terms of the effect of the trapping of resonance line radiation (opacity).…”

“…They found that the value of the ratio (for which they used the symbol B) was significantly different from the value of less than 0.515 predicted by theory and suggested an explanation in terms of the effect of the trapping of resonance line radiation (opacity). It is of good quality and has yielded a set of results of comparable significance to that of Sylwester et al (1986). For this reason we decided that it was important to seek confirmation of the result using the Flat Crystal ~Spectrometer (FCS) on the Solar Maximum Mission spacecraft (Acton et aL, 1980).…”