The centroids of the emission lines that were analyzed in the spatially resolved SERTS-93 slit spectra exhibited variations with position along the slit. In order to determine whether these shifts are manifestations of real mass motions, we derived lower limits V_min on statistically significant velocity shifts by the following method: we used spatially averaged spectra from the longest two exposures to determine two values of the centroid wavelength of every line (so that the differences provide estimates of the repeatability of line wavelength measurements), and we added to this the standard deviation of the wavelength shifts for each different line in the spatially resolved spectra. (For every one of the spatially resolved spectra, the relative wavelength scale was fixed so that the wavelength of the strong He II line in the spatially averaged spectrum is at a wavelength of exactly 303.782 Å.)
The Figures below show the measured velocity shifts for (a) He II 303.8 and (b) Fe XVI 335.4, in km/s, along the SERTS-93 slit in NOAA region 7563. Negative values correspond to upflows, and positive to downflows. The solid horizontal line in each frame shows a zero shift for reference. For Fe XVI 335.4, the horizontal dotted lines indicate V_min. For the He II line, no repeatability uncertainty measurements were available since this line's wavelength was defined to be exactly 303.782 Å in each spatially averaged spectrum; the horizontal dotted lines in the He II frames indicate 1, 2, and 3 sigma. It is evident that wavelength shifts are quite small, <10 km/s, and do not provide statistically significant detections of Doppler shifts due to mass motions. A similar analysis of the Mg IX 368, Fe XIII 348, Si XI 303, Fe XIV 334, and Fe XV 284 lines yields the same conlculsion: We do not detect Doppler shifts due to mass motions in the hot EUV emission lines in either the active region or the quiet-sun.
"The Structure and Properties of Solar Active Regions and Quiet-Sun Areas Observed in Soft X-Rays with Yohkoh/SXT, and in the Extreme Ultraviolet with SERTS," J. W. Brosius, J. M. Davila, R. J. Thomas, J. L. R. Saba, H. Hara, and B. C. Monsignori-Fossi, Ap. J. 477, 969 (1997).
Last Revised: Wednesday, 29-Nov-2006 07:36:52 EST
Responsible NASA Official: joseph.davila@gsfc.nasa.gov
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