Emission in Hydrogen Balmer Lines and Continuum in Flash Spectrum of 1952 Total Solar Eclipse at Khartoum, Sudan.

Abstract

Analysis of the spectrograms of the chromospheric flash obtained at the 1952 solar eclipse in Khartoum, Sudan, presented serious photometric problems. Standardixing exposures made at Khartoum were not successful because of a posteclipse failure of the film-advance mechanism. Characteristic curves obtained from standard lamp exposures made in Boulder after completion of the expedition could not be trusted to represent the photometric properties of the eclipse films and were principally useful as a first approximation to the curves representing the eclipse spectrograms. Methods were developed that, in spite of these problems, allowed entirely reliable determinations of the characteristic curves of the eclipse films. A thorough, independent check on the consistency and accuracy of the final curves was possible, and its result was entirely satisfactory. Change with wave length of fiim sensitivity, atmospheric absorption, and optical constants of the spectrographs were evaluated and included in the photometry. The integrated intensities of the hydrogen Baimer lines from H8 to H31 and at four wave lengths in the Balmer continuum were measured at two points on the east limb on seventeen ultraviolet spectrograms; and the intensities of Hp, H , and H were measured at one of these points on nineteen visible spectrograms. The observations extend from 100 to 6300 km, with a height resolution of 108 1cm throughout most of the low chromosphere. Preliminary interpretation of the line intensities revealed that the effects of self-absorption were pronounced and also demonstrated that there were large departures from thermodynamic equilibrium, in the sense that the b ' s were greater than 1 at 1000 km and increased with height. A preliminary mterpretation of the continuum data gave a chromospheric model characterized by a large increase of temperature with height and a relatively low electron-density gradient. A more detailed analysis of the data is in progress.