Recently, Grossi et al. (1971) have studied the line excitation in a flare of 3b Importance which occurred on March 12, 1969 near the western limb (N 12, W 78). Their spectra were taken in the H and K lines region from 23920-3975 A, with the vacuum spectroheliograph of the San Miguel observatory (Paneth and Seibold, 1969). One of the most interesting features of these spectra was a remarkable continuum emission in the region studied. Unfortunately the plate had no photometric calibration, so it was not possible to make a spectrophotometric study of that interesting spectrum.
Continuous emission is not often recorded in flare spectra, and it is best observed in flares which occur near the limb. The origin of this emission is still controversial, many authors have proposed different mechanisms. These mechanisms can be divided according to the location of the layers in which the emission has its origin; some mechanisms such as synchrotron and Compton radiation situate the emission in high levels of the chromosphere and in the corona. The other kind situates the phenomenon in the photosphere, and in this type we may mention some overheating or a penetration of the flare into the upper layers of the photosphere. All these possibilities have been summarized by Svestka (1966).
As the spectral study of this kind of phenomenon is very important, we have tried to do some further work with the material obtained at San Miguel. For this purpose we have compared the behaviour of the spectral lines of different elements with the variation of the excitation potential. In this way we should be able to decide about the location of the continuum because if the emission originates in the upper layers of the flare all the spectral lines should be affected in the same way, but if the location is very low in the atmosphere the lines of different excitation potential should be affected in a different manner.
Therefore we have studied separately the part of the flare spectrum showing the continuous emission and that outside it, and we have classified the emission increase in the continuum in the following way: 0. No change inside and outside the continuum. 1. Change uncertain. 2. Little change. 3. Moderate change.