Abstract

Radio images and spectra of an eruptive prominence were obtained from simultaneous multifrequency observations at 36 GHz, 89 GHz, and 110 GHz on 28 May 1991 with the 45-m radio telescope at Nobeyama Radio Observatory (NRO), the National Astronomical Observatory, Japan (NAOJ). The ratio spectra indicated that the optical depth is rather thick at 36 GHz whereas it is thin at 89 and 110 GHz. The H alpha data, taken at Norikura Solar Observatory, NAOJ, suggest that the eruption of an active region filament was triggered by an H alpha flare. The shape and position of the radio prominence genearally coincided with those of H alpha images. The radio emission is explained with an isothermal cool thread model. A lower limit for the electron temperature of the cool threads is estimated to be 6100 K. The range of the surface filling factors of the cool threads is 0.3-1.0 after the H alpha flare, and 0.2-0.5 in the descending phase of the eruptive prominence. The column emission measure and the electron number density are estimated to be of the order of 10(exp 28) cm(exp -5) and 10(epx 10) cm(exp -3), respectively. The physical parameters of a quiescent prominence are also estimated from the observations. The filling factors of the eruptive prominence are smaller than those of the quiescent prominence, whereas the emision measures and the electron densities are similar. These facts imply that each cool thread of the prominence did not expand after the eruption, while the total volume of the prominence increased.