Photoelectric spectrophotometry of the Cygnus Loop

Photoelectric measurements of line and continuum intensities at three places in the Cygnus Loop are presented. It is shown that the Balmer decrement can be interpreted as being produced by recombination with a small contribution of collisional excitation. The. continuum intensities indicate an additional source of continuum beyond that produced purely by radiative recombinations, and it is suggested that collisional excitation of the hydrogen 2s level is a likely mechanism for production of the additional continuum. Temperatures derived from [0 iii] line intensities are in the range of 39,000 to 49,000 K, while [0 ii], [N ii], and [S ii] line intensities give temperatures from 8400 to 17,400 K. Electron densities derived from [0 ii] line intensities are 100275 cm - , and from [S ii] line intensities are 5201500 cm - . Comparison with theoretical calculations of the structure of a radiating shock by Cox shows excellent quantitative agreement for two of the positions observed, but for the third the agreement is poorer. Subject headings: nebulae - spectrophotometry - supernova remnants