Flare Stars and Solar Bursts: High Resolution in Time and Frequency,
TUFTS UNIV MEDFORD MA DEPT OF PHYSICS AND ASTRONOMY
Pagination or Media Count:
Coronal loops on the Sun and nearby stars are investigated using observations at 20 cm wavelength with high resolution in time and frequency. Observations of the dwarf M star AD Leonis with high time resolution using the Arecibo Observatory have resulted in the discovery of a quasi-periodic train of circularly polarized spikes with a mean periodicity of 32 or - 5 ms and a total duration of 150 ms. The individual spikes had rise times of or 5 ms, leading to an upper limit to the linear size L or 1.5 x 10 to the 8th power cm for the spike emitter. This size is only 0.005 of the estimated radius of Ad Leonis. Provided that the emitter is symmetric, it has a brightness temperature of T sub B or 10 to the 16th power K, suggesting a coherent burst mechanism such as an electron cyclotron maser. Coronal oscillations might modulate the maser output, producing the quasi-periodic spikes. Observations at closely spaced wavelengths, or high frequency resolution, using the Very Large Array have revealed narrow-band structure Delta nunu or 0.01 in solar bursts and in the slowly varying radiation of the dwarf M star YZ Canis Minoris. The narrow-band emission cannot be explained by continuum emission processes, but it might be attributed to electron cyclotron maser radiation. Maser action at the second or first harmonic of the gyrofrequency implies magnetic field strengths of 250 and 500 G, respectively. Thus, observations with high resolution in time and frequency suggest coherent processes in the coronae of the Sun and dwarf M stars. The scientific potential of these discoveries may be best fulfilled by the construction of a solar stellar synthesis radiotelescope.