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Session 9 - Instruments, Techniques.
Display session, Monday, June 09
South Main Hall,

[9.10] Ultraviolet Interstellar Linear Polarization. IV. Cross-Calibration Between the Wisconsin Ultraviolet Photo-Polarimeter Experiment and the Faint Object Spectrograph

M. J. Wolff (SSI), G. C. Clayton (LSU), R. G. Allen (Steward Obs.), B. L. Babler, M. R. Meade, K. H. Nordsieck, C. M. Anderson (SAL/U. Wisconsin), P. G. Martin (CITA/U. Toronto), D. C. B. Whittet (RPI)

The Wisconsin Ultraviolet Photo-Polarimeter experiment (WUPPE) and the Faint Object Spectrograph (FOS) started gathering UV spectropolarimetry from space in 1990. Although both instruments are no longer operating, each observed a wide range of polarimetrically interesting objects before being retired. We examined the polarimetric calibration of each instrument and compared the absolute calibrations through the use of the limited sample of ``standard stars'' observed by both instruments. We found:

\bullet The internal polarization calibration of FOS for the pre- and post-COSTAR eras are consistent within the estimated statistical and systematic errors. The much higher post-COSTAR instrumental polarization is stable and correctable.

\bullet The internal polarization calibration of WUPPE for Astro-1 and -2 are consistent within the estimated statistical and systematic errors. However, there appears to be some variation in region to the red of 3.5 \micron^-1, where the unpolarized star data show a larger dispersion. This may be related to focus issues.

\bullet The systematic errors are estimated to be 0.1%+ 0.02p(%) and 0.1%+0.1p(%) for pre- and post-COSTAR datasets, respectively. For WUPPE, the systematic error is 0.05%+0.05p(%).

\bullet The observations in common between FOS and WUPPE for HD 197770, 161056, and 161961 show that the data can be compared on same basis. Each calibration produces consistent results.

This work was supported by NASA grants NAS5-26777, NAG5-3032 and NAG5-3032.

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