RADIOMETRIC CALIBRATION OF SUMER - REFINEMENT OF THE LABORATORY RESULTS UNDER OPERATIONAL CONDITIONS ON SOHO

The radiometric calibration of the solar telescope and spectrometer SU MER was carried out in the laboratory before delivery of the instrumen t for integration into the SOHO (Solar and Heliospheric Observatory) s pacecraft. Although this effort led to a reasonable coverage of the wa velength range fi-om 53.70 to 146.96 nm, uncalibrated portions of the sensitivity curves remained before SUMER became operational in early 1 996. Thereafter it was possible to perform extrapolations and interpol ations of the calibration cut-yes of detector A to shorter, longer, an d intermediate wavelengths by using emission line pairs with known int ensity ratios. The spectra of the stars alpha and rho Leonis were also observed on the KBr (potassium bromide) photocathode and the bare mic rochannel plate (MCP) in the range from 120 to 158 nm. In addition, th e sensitivity ratios of the KBr photocathode to the bare MCP were dete rmined for many solar Lines as well as the I-I I Lyman and the thermal continua. The results have been found to be consistent with published laboratory data. The uncertainty is +/-15% (I sigma) in the wavelengt h range I from 54 to 125 nm. (C) 1997 Optical Society of America.