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O. Titov, S. Lambert, B. Soja, F. Shu, A. Melnikov, J. McCallum, L. McCallum, M. Schartner, A. de Witt, D. Ivanov, A. Mikhailov, S. Yi, C. Wen, B. Xia, M. Ishigaki, S. Gulyaev, T. Natusch, S. Weston:
"Observations of radio sources near the Sun";
Talk: 24th Meeting of the European VLBI Group for Geodesy and Astrometry, Gran Canaria, Spain; 2019-03-17 - 2019-03-19.

Geodetic Very Long Baseline Interferometry (VLBI) data are capable of measuring the light deflection caused by the gravitational field of the Sun and large planets with high accuracy. The parameterγ of the parametrized Post-Newtonian (PPN) formalism estimated using observations of reference radio sources near the Sun should be equal to unity in the general relativity. We have run several VLBI experiments tracking reference radio sources from 1 to 3 degrees from the Sun. The best formal accuracy of the parameterγ achieved in the single-session mode is less than 0.01 percent, or better than the formal accuracy obtained with a global solution included all available observations at arbitrary elongation from the Sun. We also present the resulting electron density model of the solar corona. The strong coronal signal contained in the observations allowed for a determination of the electron density with unpreceded precision. It was for the first time possible to estimate both power-law parameters (hypothetical electron density at the Sunīs surface and the radial falloff parameter) at the same time. We are planning more experiments starting from 2020 using better observing conditions near the minimum of the Solar activity cycle.

http://www.oan.es/evga2019/EVGA2019_PDF/O210_EVGA2019_Titov.pdf