The three-element interferometer of the National Radio Astronomy Observatory was used to observe the Sun at 3.7 and 11.1 cm wavelengths during the period June 5-9, 1973. The baselines of the interferometer were 900, 1800 and 2700 meters, with maximum angular resolution of 3" at 3.7 and 9" at 11.1 cm wavelengtt s. The objective of the observing program was to look for the Sun's fine structure at the limb, in active regions and in flare-associated burst sources. In this note, we present the results of observations of fine structure in an active region located at N14 W19 on June 8 (see Figure 1).
The observations consisted of tracking an active region from sunrise to sunset. The NRAO interferometer tracks sources only at the sidereal rate. Therefore, it was necessary to update pointing frequently in order to track the Sun. Also, in order to obtain consistent information of the fringe phase (phase computed from the position c~, 6 assumed for the source) it was necessary to use the exact position e, 6 of the region at any instant. For these reasons, the position of the source was updated every 3 rain, taking into consideration the difference between sidereal and solar rates, the solar rotation and parallax. The accuracy of the source position at any instant used in this manner was better than 3".
The interferometer was operated in dual mode taking data alternately at 3.7 and 11.1 cm wavelengths every 30 s. The parametric amplifier was turned off for the solar observations. The fringe amplitude and phase were obtained by fitting a sine curve to the correlator output over an interval of 30 s. Since the interferometer takes a data point every 30 s, allowing for the time to update the telescope position, 5 data points were taken every 3 min. Obviously, during the three minutes between position updates the Sun drifts relative to the beam. In order to correct for this, the phase for each 30-s record was adjusted during data reduction to compensate for the drift. No adjustment was necessary for the amplitudes of each 30-s record. Small systematic error in the phases are possible for sources away from the center of the beam due to solar rotation. This effect was not corrected for, since the region studied was only 1'.5 arc away from the center of the beam, and this effect was not significant.
The observed fringe amplitude and phase were used to obtain the synthesized map of the region. The synthesized maps of the region at 3.7 and 11.1 cm are shown in Figures 2a and2b. The map coordinates are given in right ascension and declination. They are provided only to indicate the scale of sizes and do not, of course, denote the