Radio Emission from Solar and Stellar Coronae.

Several problems in radiophysics are explored utilizing new and unique observations. Polarization measurements of two types of solar bursts--Reverse Drift Pairs and Type V bursts--allowed identification of the radiation as due to fundamental plasma emission for RDPs and harmonic plasma emission for Type Vs. Two other types of solar radio burst--Type II (shock related) and Type IV--observed at Culgoora, Australia, are studied with the aid of Coronagraph/Polarimeter (C/P) observations. Together, the radio and C/P data indicate the presence of two separate shocks in the coronal transient event of 1980 June 29. One shock, without radio emission, led the transient and was driven by it. Estimates of the density enhancement caused by the shock give Mach number l.2 < M(,A) < 3 and, hence, magnetic field strength in the ambient corona 0.05 < B < 0.12 gauss. The second shock, which gave rise to the radio emission, was associated with the loops. The Type II sources appeared to lie behind the leading edge of the loops, and a measurement of the density from the C/P images showed that only behind the loops was the density high enough to account for the plasma emission. The second shock is interpreted as a blast-wave, initiated by the impulsive flare, which traversed the transient material and weakened when it encountered the faster moving, upper part of the transient. The Type IV burst observed at 80 MHz in the same event showed slight outward movement in association with a rising of the relevant plasma level as transient material entered the corona. The characteristics of the sources observed at 80 and 43 MHz suggest that plasma radiation at the second harmonic was the probable emission mechanism. The possibility of gyro-synchrotron emission is explored, and it is found that the sources could have been due to this mechanism only if the magnetic field strength at 2.5R(,0) was > 2.8 gauss. Finally, the discovery of quiescent microwave emission from solar-type stars is discussed. Two sources, (chi)('1) Ori and UV Cet, were detected. The emission is interpreted as gyroresonance emission from hot extended coronae; free-free emission is shown to be unlikely.