High-resolution observation and detailed photometry of a great H? two-ribbon flare

Abstract

A great Hα two-ribbon flare of 12 October, 1981 was observed with the Domeless Solar Telescope at the Hida Observatory and its detailed photometry was made with a two dimensional microdensitometer. The principal results are as follows: (1) The impulsive phase of the flare started with the progressive brightenings of flare points forming the front lines of the Hα two ribbons at both sides of the magnetic neutral line. These are followed by the explosive expansion of Hα two ribbons at the main impulsive phase. (2) Three typical shapes of Hα light curves were found. The type 1 light curve is characterized by the primary impulsive rise and rapid fall of intensity. The light curve of type 3 has no impulsive component but has a very gradual maximum. The type 2 profile attains the main gradual maximum with a few small impulsive peaks. These different types of light curves are made by different heating mechanisms, those are electron precipitation, heat conduction and soft X-ray radiation respectively. (3) The light curve of total intensity, which was made by integrating Hα - 1.0 A intensities of the whole main Hα flare region, shows a primary impulsive peak and a later gradual maximum. The former peak coincides in time with that of the hard X-ray emission. The latter maximum is well correlated with the soft X-ray maximum. (4) The brightest flare points with time profiles of type 1 are closely related to the impulsive hard X-ray emissions of highest energy.