Improvement of Corona Temperature and Velocity Determination Method Using a Coronagraph Filter System

We have developed a methodology to determine the coronal electron temperature and solar wind speed using a four filter coronagraph system. The method developed so far have been applied to total eclipse observation and have yielded plausible results. The current methodology starts from the assumption that 1) coronal free electrons are isothermal and 2) coronal free electrons have spherically symmetric distrubution. However, the actual solar corona differs significantly from the two assumptions above. The coronal electron density is not spherically symmetric due to streamers, plumes, and coronal loops, and the electron temperature is also expected to increase rapidly with distance from the sun. We will discuss how to determine the temperature and wind speed of the corona in the case of corona with thermal structures and non-spherical symmetric electron density.