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P. S. Kortenkamp, S. R. Spangler, R. L. Mutel (The University of Iowa)
We report on very long baseline interferometer (VLBI) observations of 15 extra-galactic radio sources viewed through the inner solar wind at heliocentric distances from 6 to 38 solar radii. The observations were carried out on September 10, 2002 with the Very Long Baseline Array (VLBA) of the National Radio Astronomy Observatory at frequencies of 2.3, 5.0, and 8.4 GHz. The analysis technique utilizes interferometer phase fluctuations caused by turbulent density irregularities along the line of sight. The power spectrum of the phase fluctuations contains information on the level of the density fluctuations and the speed at which the irregularities move relative to the antennas. The technique is most sensitive to irregularities with sizes of order the interferometer baseline length. The current observations differ from previous ones in three ways. (1) The observed “constellation” of radio sources provides nearly simultaneous measurements over a much larger range of both heliographic latitude and heliocentric distance than previous VLBI observations. (2) LASCO images of the Sun’s corona are available from the period of observation. These white-light images document the coronal density structure and dynamics at the time of the observations and aid in understanding the results of the power spectra analysis. Specific information of interest includes the position of streamers with respect to observed sources and the documentation of flares or coronal mass ejections which may have occurred during the observing session. (3) Contemporaneous coronal models have been created (through collaboration with Pizzo & Odstrcil) which provide three dimensional bulk density and velocity characteristics of the environment traversed by the lines of sight. Such knowledge allows for improvements to the simple, though appropriate, approximations used in previous analyses. This research was supported by grants ATM99-86887 and ATM03-11825 from the National Science Foundation.
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Bulletin of the American Astronomical Society, 36 #2
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