Observations of Active Prominence and Coronal Magnetic Fields.
Abstract
The magnetograph of the High Altitude Observatory was used to obtain more than 200 measurements of the longitudinal magnetic field in limb prominences in and near active regions with the Ha line. A few additional observations were made with the D2, D3, and Hfl lines. Seven measurements of the coronal field with the N5303 line were attempted. Noise in the observations was generally less than 5 gauss. Field strengths in active prominences ranged from undetectable to about 150 gauss. The observed fields tend to decrease with increasing height unlike the field of quiescent prominences (Rust, Astrophys. J. 150, 313,1967). The field frequently appears to be oriented predominantly along the axis of both active and quiescent prominences. Simultaneous radial velocity recordings show periodic oscillations in about 15% of the active prominences and about 30% of the quiescent prominences observed; no evidence for a corresponding magnetic field oscillation was found. A few surges showed strong longitudinal fields (100 gauss) but most had fields less than 30 gauss. Large surges are usually associated with weak fields and strong fields with small surges. Field strengths from 10 to 60 gauss were observed in loop prominences. The spatial characteristics of the loop fields are similar to those of the fields inferred from potential theory but the observed strengths are about ten times greater. Coronal magnetic fields are not easy to observe. Our best measurements of the longitudinal field strength in the corona about 30,000 km above two moderately active regions are 1.5 and 2.0 gauss. Nearby prominences showed fields two to three times stronger.
- Publication:
-
The Astronomical Journal Supplement
- Pub Date:
- 1968
- Bibcode:
- 1968AJS....73R..62H