The new HiVIS spectropolarimeter and spectropolarimetric calibration of the AEOS telescope.
HARRINGTON D.M., KUHN J.R. and WHITMAN K.
Abstract (from CDS):
We have designed, built, and calibrated a new spectropolarimeter for the HiVIS spectrograph (R ∼ 12,000-49,000) on the Advanced Electro-Optical System (AEOS) telescope. We have also conducted a polarization calibration of the telescope and instrument. In this paper, we introduce the design and use of the spectropolarimeter, in addition to a new data-reduction package we have developed, and then discuss the polarization calibration of the spectropolarimeter and the AEOS telescope. We used observations of unpolarized standard stars at many pointings to measure the telescope-induced polarization and compare it with a Zemax model. The telescope induces polarization of 1%-6%, with a strong variation with wavelength and pointing, consistent with the expected altitude and azimuth variation. We then used scattered sunlight as a linearly polarized source to measure the telescope's spectropolarimetric response to linearly polarized light. Finally, we made an all-sky map of the telescope's polarization response to calibrate future spectropolarimetry.