Revisiting the determination of the coronal heating function from Yohkoh data

Results on the coronal heating function seem to strongly depend on the employed type of multitemperature modeling along the line of sight. Instruments with broadband temperature filters cause more temperature confusion than those with narrowband temperature filters. A possible bias of broadband filters is the hydrostatic weighting of multitemperature loop systems, which mimic a temperature increase with altitude and thus yield a preference for looptop heating. In this Letter we revisit a loop system previously analyzed by Priest et al., for which they found that the coronal heating is likely to be uniform in the temperature range between 1.6 and 2.2 MK. As an alternative scenario, we use standard hydrostatic solutions here (with vanishing conductive flux in the transition region). We show that hydrostatic solutions with a uniform heating function throughout the corona and transition region lead to unphysical solutions for the column depth and the altitude of the loop footpoints, while a footpoint-heating model yields acceptable physical solutions for a heating scale height of s(H) approximate to 13 +/- Mm. The positive temperature gradient with height (which is also found in filter- ratio temperatures of other Yohkoh data) can be explained by the hydrostatic weighting bias resulting from hot loops (T-max approximate to 2.6 MK) embedded in a cooler (T-max approximate to 1.0 MK) background corona.