The quiet-sun differential emission measure from radio and UV measurements

In the present work we combine UV and radio observations of the quiet Sun to determine the differential emission measure (DEM) of the average quiet solar atmosphere from the photosphere ( 5600 K) to the corona. UV line intensities have been used to constrain the DEM above 30,000 K, and the radio spectrum from 1.5 to 345 GHz has been used to extend the DEM determination down to 5600 K. Radio observations are shown to provide a much more reliable diagnostic tool for DEM determination than UV and EUV lines at T < 30; 000 K. The resulting average quiet-Sun DEM that we found is in excellent agreement with curves from the literature for temperatures larger than 60,000 K, but is lower than previous determinations by more than 1 order of magnitude in the 10,000-30,000 K temperature range. The present work determines the DEM below 10,000 K for the first time, in a temperature region where UV and EUV lines cannot be used.