Nonpotential Broadening of UV Lines Observed at the Limb of the Quiet Sun
Abstract
We have done a spectroscopic study of the solar transition region using high resolution UV & EUV data obtained by SUMER) on board SOHO. Optically thin and conspicuous emission lines observed at the solar limb are carefully selected to acquire average values of physical parameters for the quiet region as a function of radial distance. Our main results found from the present study can be summarized as follows. 1) Nonthermal velocities estimated from various UV lines do not decrease with height at least within one total line intensity scale height above the limb. 2) Nonthermal velocity distribution with temperature is very similar to that of the disk center, in the sense that its peak is located around 2E+5 K, but the value is systematically larger than that of the disk. 3) It is found that nonthermal velocity is inversely proportional to quadratic root of electron density up to about 10 arc seconds above the limb, i.e. ~ Ne**(-1/4), implying that the observed nonthermal broadening can be attributed to Alfven waves passing through the medium. 4) Electron density estimated from the O V 629/760 line ratio is found to range from about 1e+10 cm-3 to 2e+10 cm-3 in the transition region.
- Publication:
-
Journal of Korean Astronomical Society
- Pub Date:
- April 2000
- Bibcode:
- 2000JKAS...33...57L
- Keywords:
-
- SUN: TRANSITION REGION;
- SUN: UV;
- SPECTROSCOPY: SUMER;
- NONTHERMAL VELOCITY