Temperature and Density Structure of Hot and Cool Loops Derived from the Analysis ofTRACEData

Abstract

We study the transversal structure (in particular the filamentation) and the longitudinal plasma stratifica- tion in two sets of solar coronal loops observed with TRACE in the 171 and 195 Apassbands. The density stratification and the thermal structuring of the plasma along the fibrils that form the loops are derived using two techniques simultaneously: (1) a filter ratio diagnostic (195/171 A ˚ ) and (2) modeling intensity profiles along the fibrils with hydrostatic models; in both techniques we remove the background flux. We find consistent values of temperature and density with both methods in the coronal structures selected. We find evidence of a very warm fibril (T � 5 � 10 6 K) and of rather cold ones (T � 2 � 10 5 K). The hot fibril appears to have a thermal structure with a maximum at the apex compatible with temperature and density stratification, dictated by energy balance, typical of a nonisothermal hydrostatic loop. The cold fibrils appear to be isothermal and are probably in dynamical conditions. Subject headings: Sun: corona — Sun: UV radiation On-line material: color figures