The polarization of the D3 emission line in prominences

International audienceOver 1,000 polarization measurements pertaining to about 90 distinct solar prominences were taken on the D 3 triplet lines of helium at 5876 A. Most of the measurements were made on quiescent prominences at the polar latitude. A typical D 3 polarization measurement in a quiescent prominence yields a degree of polarization of about 0.020 and a polarization deviation of plus or minus 15 deg. Average height variations of the degree of polarization and angular deviation of polarization were also obtained. The observed polarizations fall below the theoretical maximum, and it is believed that in some cases one is dealing with prominence regions in which there is no nonmagnetic depolarization or no magnetic depolarization. Several possible nonmagnetic depolarization effects are likely to decrease in the uppermost part of prominences, so that magnetic depolarization must be larger at the top of quiescent prominences