First Results from 5-Element Observations with the OVRO Solar Array

Astronomy and Astrophysics – Astronomy

Scientific paper

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Scientific paper

We report the first synthesis imaging results using the 5 antennas of the newly expanded solar array at Owens Valley Radio Observatory. The observations were made on 1991 Oct 24 and give the spatial and spectral structure of the complex active region NOAA 6891 as well as the spatial, spectral, and temporal structure of three flares that occurred during our observations. We show aperture synthesis maps of the active region from 1.2 to 7 GHz, with spatial resolution from 60'' to 9'' over the same range, and plot brightness temperature spectra for various points in the maps to show the region of dominance of free-free emission versus the region of dominance of gyroresonance emission. From the free-free dominated spectra we can deduce the coronal column density and temperature as a function of position over the active region. Where the source is dominated by gyroresonance emission, the spectra can be used to determine the magnetic field strength at the base of the corona (see the paper by Lee, Gary, and Hurford also being presented at this meeting). We also investigate the three flares that occurred during our observations, using frequency synthesis to map the spatial structure over relatively broad frequency ranges. We find several interesting results, including a radio emission source with no accompanying Hα emission and motion of the radio source along the spreading Hα ribbon. These results represent the first, but not necessarily the best-suited, observations of active regions and flares with the new OVRO Solar Array. They serve to show the tremendous capability of the instrument to resolve the ambiguities that for so long have plagued radio studies because simultaneous spatial and spectral observations were not available.

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