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J. W. Brosius (Raytheon ITSS), R. J. Thomas, J. M. Davila (NASA/GSFC)
We used slit spectra from the 1995 flight of Goddard Space Flight Center's Solar EUV Rocket Telescope and Spectrograph (SERTS-95) to measure wavelength shifts of coronal emission lines across the core of NOAA active region 7870 relative to its immediate surroundings (its ``edge"). This method circumvents the absence of reliable laboratory wavelengths for the observed lines by using lines from the edge spectrum as effective standards. We derived the SERTS-95 wavelength calibration from measurements of a post-flight laboratory spectrum containing 28 He II and Ne II EUV standard wavelengths known to high accuracy. Wavelength measurements for lines of He I, Ne III, and additional lines of Ne II in the laboratory calibration spectrum provide more accurate values than were previously available, enabling these lines also to serve as future calibration standards. Six solar lines were chosen for this study because they are free from known blends and are either intrinsically strong or near the SERTS-95 peak sensitivity: He II at 303.78 Å, Fe XII at 193.51 Å, Fe XIII at 202.05 Å, Fe XIV at 211.33 Å, Fe XV at 284.15 Å, and Fe XVI at 335.41 Å. The iron ions are the hottest ions ever used for this type of analysis. All six lines reveal statistically significant variations in their measured wavelength shifts across the active region core, including mixtures of blueshifts and redshifts, indicating a dynamic, turbulent corona. For each line we calculated weighted-average Doppler velocities, obtaining 3.3 ±1.1 km s-1 for He II, 5.2 ±1.6 km s-1 for Fe XII, 0.7 ±1.5 km s-1 for Fe XIII, -2.1 ±1.4 km s-1 for Fe XIV, 1.0 ±1.1 km s-1 for Fe XV, and -1.1 ±0.8 km s-1 for Fe XVI. This suggests a net upflow of heated material cospatially and cotemporally with a net downflow of cooler material. We acknowledge NASA support for this research.
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s follows:
http://orpheus.nascom.nasa.gov/serts/