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C. W. Engelke (Boston College), S. D. Price (Air Force Research Laboratory), C. Paxson, T. L. Murdock (Frontier Technology, Inc.)
The MSX program calibrated the SPIRIT III responsivity on orbit with six calibration experiments that tested the various operating modes or the sensor. On the average, two of these experiments were conducted each week over a nine month period before the end of the mission. Usually, each experiment observed two out of nine standard infrared calibration stars and each observation nominally consisted of 20 to 80 individual measurements. A residual variation of SPIRIT III response with focal plane temperature was found and corrected. The corrections were normalized to the absolute in-band fluxes from Sirius specified by Cohen et al., which scales the SPIRIT III calibration to this star. The MSX photometry on the infrared calibration stars agrees well with that predicted from the absolute spectra of Cohen and his colleagues if the flux from Sirius is increased by about 1%. Discrepancies were observed for \beta Peg, which MSX found to be variable, and \alpha Lyr, for which MSX observed a flux excess at wavelengths longer than 14 \mum that is consistent with emission from the circumstellar dust shell known to surround this star. MSX validated the absolute flux for eight of the Cohen et al. infrared standard stars with measurements errors of a percent or less and requires a statistically significant increase of 1% in the infrared flux of Sirius.
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Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.