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Session 15 - The Sun and Solar Wind.
Display session, Monday, June 08
Faraday rotation measures the path integral of the product of electron density and line of sight component of the magnetic field from the observer to a source of linearly polarized radio emission. For our observations, the line of sight passes through the solar corona. These observations were made with the NRAO Very Large Array at frequencies of 1465 and 1635 MHz. Observations at two frequencies can confirm the \lambda^2 dependence of position angle rotation characteristic of Faraday rotation. We observed the extended radio source 0036+030 (4C+03.01) on March 28, 1997, when the source was 8.6 R_ødot from the center of the Sun. Nearly continuous observations were made over an 11 hour period. Our observations measure an average rotation measure (RM) of about +7 radians/m^2 attributable to the corona. The RM showed slow variations during the observing session, with a total change of about 3 radians/m^2. This variation is attributed to large scale gradients and static plasma structures in the corona, and is the same for two source components separated by 30 arcseconds (22000 km). We have also detected RM variations on time scales of 15 minutes to one hour, which may be coronal Alfven waves. We measure an rms variation of 0.57 radians/m^2 for such fluctuations, which is comparable to previous reports.
Program listing for Monday