Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004aas...205.4304k&link_type=abstract
American Astronomical Society Meeting 205, #43.04; Bulletin of the American Astronomical Society, Vol. 36, p.1412
Astronomy and Astrophysics
Astronomy
Scientific paper
I report on very long baseline interferometer observations of extra-galactic radio sources viewed through the inner solar wind. The turbulent interplanetary medium induces phase fluctuations in the incident radio waves resulting in a scatter broadened source. The observations were carried out on September 30, 1999 and September 10, 2002 with the Very Long Baseline Array of the National Radio Astronomy Observatory at frequencies of 2.3, 5.0, and 8.4 GHz. The 1999 observations were of the two strong sources 3C273 (at a heliocentric distance of 18 RSun) and 3C279 (30 RSun), viewed above the north solar pole and in the ecliptic plane respectively. The 2002 observations employed a "constellation" of 15 somewhat weaker radio sources to provide nearly simultaneous measurements over a large range of both heliographic latitude and heliocentric distance (6 RSun to 38 RSun). The main 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. This technique is most sensitive to irregularities with sizes of order the interferometer baseline length. A second analysis technique investigates the visibility function of the broadened sources in an attempt to characterize the size and shape of the scattering function. In addition, contemporaneous coronal models have been created (through collaboration with Dusan 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 some simple, though appropriate, approximations used in the above analysis. The results, which compare well with previous observations, reveal radially aligned anisotropic scattering for some sources and show relatively significant temporal and spatial variations in turbulence parameters. This research was supported by grants ATM99-86887 and ATM03-11825 from the National Science Foundation.
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