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SUMER observations of Doppler shift in the quiet Sun and in an active region
D. Banerjee and
Received 26 March 1999 / Accepted 21 June 1999
The UV spectral lines formed at transition region temperatures in the solar atmosphere, show a prevailing redshifted emission. Using the Solar Ultraviolet Measurements of Emitted Radiation spectrometer flown on the Solar and Heliospheric Observatory spacecraft, we measure the amount of line shift as a function of the temperature for several spectral lines formed in the range between and K. We analyze spectrograms relative to the quiet Sun and to the active region NOAA. The velocities derived are increasing from a redshift of at K to at K for the quiet Sun, and to at K for the active region. At higher temperature an opposite behaviour is observed. In the quiet Sun a blueshift of is observed at the Ne VIII formation temperature (K), while in the active region, a blue-shifted value around is observed for the same spectral line. The finding of blueshift in Ne VIII is due to the adoption of a new rest wavelength of 770.428 Å. By K the blueshift is in the active region as measured by Fe XII 1242.
Key words: Sun: atmosphere Sun: transition region Sun: UV radiation
Send offprint requests to: L. Teriaca
Online publication: September 2, 1999