Spatial distribution of XUV emission and density in a loop prominence

Abstract

We have studied the spatial distribution of XUV emission in the 14 August, 1973 loop prominence observed with the NRL spectroheliograph on Skylab. The loop prominence consists of two large loops and is observed in lines from ions with temperatures ranging from 5 × 10⁴ K to 3 × 10⁶ K. The loops seen in low temperature (≲10⁶K) lines such as from He ii, Ne vii, Mg vii, Mg viii, and Si viii are systematically displaced from loops seen in higher temperature lines such as from Si xii, Fe xv, and Fe xvi. The cross section of the loop, particularly in cooler lines is nearly constant along the loop. For hotter loops in Si xii, Fe xv, and Fe xvi, however, emission at the top of the loop is more intense and extended than that near the footpoints, which makes the loops appear wider at the top.

There is no evidence that the 14 August loop prominence consists of a cooler core surrounded by a hot sheath as in some active region and sunspot loops reported by Foukal (1975, 1976). Rather, the observed spatial displacement between cooler and hotter loops suggest that the 14 August loop prominence is composed of many magnetic flux tubes, each with its own temperature.