MG IX EMISSION-LINES IN AN ACTIVE-REGION SPECTRUM OBTAINED WITH THE SOLAR EUV ROCKET TELESCOPE AND SPECTROGRAPH (SERTS)

Theoretical electron-temperature-sensitive Mg IX emission line ratios are presented for R1 = I(443.96 angstrom)/I(368.06 angstrom), R2 = I(4 39.17 angstrom)/I(368.06 angstrom), R3 = I(443.37 angstrom)/I(368.06 a ngstrom), R4 = I(441.22 angstrom)/I(368.06 angstrom), and R5 = I(448.2 8 angstrom)/I(368.06 angstrom). A comparison of these with observation al data for a solar active region, obtained during a rocket flight by the Solar EUV Rocket Telescope and Spectrograph (SERTS), reveals excel lent agreement between theory and observation for R1 through R4, with discrepancies that average only 9%. This provides experimental support for the accuracy of the atomic data adopted in the line ratio calcula tions, and also resolves discrepancies found previously when the theor etical results were compared with solar data from the S082A instrument on board Skylab. However in the case of R5, the theoretical and obser ved ratios differ by almost a factor of 2. This may be due to the meas ured intensity of the 448.28 angstrom line being seriously affected by instrumental effects, as it lies very close to the long wavelength ed ge of the SERTS spectral coverage (235.46-448.76 angstrom).