Doppler shifts in the quiet-sun transition region and corona observed with SUMER on SOHO

New observations of systematic red shifts of transition region and coronal lines obtained with SUMER (Solar Ultraviolet Measurements of Emitted Radiation) on SOHO (the Solar and Heliospheric Observatory) are presented. With the extensive wavelength coverage of SUMER it is possible to extend the measurements of the red shifts to much higher temperatures compared to previous instruments. We find lines formed in the upper transition region (e.g. O V, S V, and S VI) to be red-shifted similar to lower temperature lines (T less than or equal to 1.8 x 10(5) K). Even hotter lines such as O VI, Ne VIII and Mg X show systematic red shifts on the order of 5 km s(-1) in the quiet Sun. This is a new and significant result since previous measurements of the red shifts were less well constrained. The behavior of the red shifts above T = 10(5) K has been somewhat controversial. In some earlier investigations the magnitude of the red shift has been found to increase with temperature, reaching a maximum at T = 10(5) K and then to decrease toward higher temperatures. Thus, our results will put new constraints on theoretical models. The measured shifts are compared to recent observations of red-shifted emission in stellar spectra obtained with the Hubble Space Telescope.