A&A Supplement series, Vol. 122, April I 1997, 181-192
Received September 23, 1995; accepted June 8, 1996
R.W. Komm, G.J. Hurford, and D.E. Gary
Send offprint request: R. Komm
Solar Astronomy 264-33, Caltech,
Pasadena, CA 91125, U.S.A.
We present first results of applying a Maximum Entropy Method (MEM)
algorithm that acts in both the spatial and spectral domains to data
obtained with the frequency-agile solar interferometer at Owens Valley
Radio Observatory (OVRO) taken at 45 frequencies in the range
. The traditional MEM algorithm does not exploit the spatial
information available at adjacent frequencies in the OVRO data, but
rather applies separately to each frequency. We seek an algorithm that
obtains a global solution to the visibilities in both the spatial and
spectral domains. To simplify the development process, the algorithm
is at present limited to the one-dimensional spatial case. We apply
our 1-d algorithm to observations taken with the OVRO frequency-agile
interferometer of active region AR 5417 near the solar limb on March
20, 1989 (vernal equinox). The interferometer's two 27 m antennas and
40 m antenna were arranged in a linear east-west array, which at the
vernal equinox gives a good match to the 1-d algorithm. Our results
show that including the spectral MEM term greatly improves the dynamic
range of the reconstructed image compared with a reconstruction without
using this information. The derived brightness temperature spectra
show that for AR 5417 the dominant radio emission mechanism is thermal
gyroresonance and we use this information to deduce the spatial
variation of electron temperature and magnetic field strength in the
corona above the active region.
keywords: Sun: corona -- Sun: magnetic fields -- Sun: radio radiation -- techniques: image processing -- techniques: interferometric