Observations of a flare spray at the solar limb on July 11, 1966

Abstract

A brief description is given of a spectacular flare spray that appeared outside the west solar limb on July 11, 1966. Observations were made at the Swedish Solar Observatory in Anacapri with (a) a 0.7 Å Hα filter combined with the flare patrol instrument, and with a 5 Å Hα filter attached to the 8 cm coronagraph, (b) in white light and with a polarization measuring device attached to the 12 cm coronagraph, (c) in the helium D₃ and Hα spectrum regions with the 20 cm solar telescope and a Babcock grating in fourth order.

During the brilliant phase the intensity of the object measured with the 0.7 Å Hα filter was 1.6 times that of the undisturbed solar surface near the centre of the disk. The object could be faintly traced even in white light outside the solar image when projected on a screen. The brilliant area had an apparent size of about 30 square degrees of the solar surface. When classified as a flare it should probably be given the importance 4n therefore.

Already a preliminary examination of the exposures secured by one of us (Stiber) for the purpose of measuring polarization, gives clear evidence of strong effects of radial polarization (vibration tangential to the limb) suggesting Thomson scattering as the main source of the continuous spectrum.

The spectra obtained show great Doppler shifts and mainly towards shorter wavelengths, corresponding to velocities of as much as 500 km per second. In the later development a rapid outflow of matter could be observed and particularly with the 5 Å Hα filter.