Emission measures and structure of the transition region of a sunspot from emission lines in the far ultraviolet

Abstract

Absolute intensities of emission lines in the wavelength range from 1200 A to 1817 A from the large sunspot in McMath region 12510 near Sun center are presented. The intensities are averaged across the umbra and penumbra of the sunspot. The observations were made with the NRL slit spectrograph on Skylab. Emission measures are derived from the measured intensities. Assuming a balance between the divergence of the conductive energy flux and the radiative energy losses, a self-consistent model of the lower transition region in the sunspot is constructed. The model gives a constant pressure of about 0.19 dyne cm-2, and a conductive flux which decreases approximately one order of magnitude between 2 × 105 K and 4 × 104 K. The temperature gradient is relatively constant, increasing slowly with decreasing temperature.