The Relationship Between UV and X-Ray Brightenings

Abstract

The relationship between structures in the transition region and corona is not well understood, and this knowledge is vital for a complete understanding of the heating of active region plasma. There have been many previous studies of active regions in the UV and X-ray using the XUV spectroheliograph onboard Skylab. Cheng et al.(1980) discuss the relationship between X-ray emission at 2–3×l0⁶ K and UV emission at 6×l0⁵ K of active region loops. They found that while hot coronal loops are lowlying and closely packed, the cool loops are fewer in number and large with smaller aspect ratios. Dere (1982) found that the transition region emission exists in loops or in segments of loops whereas the coronal emission is always found in loops. Transition region loops and coronal loops were found not to exist coaxially. Feldman & Laming (1994) conclude in their study that the cold and hot loops sometimes appear to occupy the same location, and also frequently the cool and hot loops emerge in different locations. They do not observe the cool plasma being part of a large structure which extends into the corona.