"First Allen Telescope Array (ATA) observations of the Sun"
Abstract: We present the first observations of the Sun with the
Allen Telescope Array (ATA). We used up to six frequencies, from 1.43 to
6 GHz, and baselines from 6 to 300 m. To our knowledge, these are the
first simultaneous multi-frequency full-Sun maps obtained at microwave
frequencies without mosaicing. The observations took place when the Sun
was relatively quiet, although at least one active region was present
each time. Outside of active regions, assuming optically thin
bremsstrahlung (free–free) coronal emission on top of an optically thick
≈10 000 K chromosphere, the multi-frequency information can be
condensed into a single, frequency-independent, “coronal bremsstrahlung
contribution function” map. This technique allows the separation of the
physics of emission as well as a measurement of the density structure of
the corona. Deviations from this simple relationship usually indicate
the presence of an additional gyroresonance-emission component, as is
typical in active regions.