OBSERVED REDSHIFTS IN THE SOLAR TRANSITION REGION ABOVE ACTIVE AND QUIET REGIONS

摘要

Solar UV spectral observations show a redshifted emission at temperatures between the chromosphere and the corona. We have measured the magnitude of the redshift as a function of the temperature using solar spectrograms from the High Resolution Telescope and Spectrograph—HRTS. The velocity derived from the average redshift is found to increase up to a temperature T ≈ 1.35 x 10~5 K in both quiet and active regions, then decrease with increasing temperature, with the rate of decrease depending critically on the laboratory wavelengths adopted for the transition region lines. This result illustrates the need for improved laboratory measurements. We find that the differential redshift between an active region and the surroundings increases smoothly with temperature, reaches a maximum velocity difference of 7 km s~(-1) at 1.35 x 10~5 K and falls abruptly to zero at 2.3 x 10~5 K. This observation is independent of the laboratory wavelengths. Suggestions regarding the origin of the redshift are confronted with the results.