Two types of solar active region feature prominent at transition region temperatures are identified in Hinode/EIS data of AR 10938 taken on 2007 January 20. The footpoints of 1 MK TRACE loops are shown to emit strongly in emission lines formed at log T = 5.4-5.8, allowing the temperature increase along the footpoints to be clearly seen. A density diagnostic of Mg VII yields the density in the footpoints, with one loop showing a decrease from 3 × 109 cm-3 at the base to 1.5 × 109 cm-3 at a projected height of 20 Mm. The second feature is a compact active region transition region brightening which is particularly intense in O V emission (log T = 5.4) but also has a signature at temperatures up to log T = 6.3. The Mg VII diagnostic gives a density of 4 × 1010 cm-3, and emission lines of Mg VI and Mg VII show line profiles broadened by 50kms-1 and wings extending beyond ± 200kms-1. Continuum emission in the short wavelength band is also found to be enhanced, and is suggested to be free-bound emission from recombination onto He+.
Publications of the Astronomical Society of Japan
- Pub Date:
- November 2007
- Sun: transition region;
- Sun: UV radiation;
- 11 pages, 9 figures, submitted to PASJ Hinode first results issue