Addition of a polarization analysis capability to the Fan Mountain near infrared camera

摘要

A small research grant from the AAS has enabled the addition of a pair of MgF2 Wollaston prism polarization analyzers to the Fan Mountain Near Infrared Camera (FanCam). FanCam is a HAWAII-1 (1K x 1K HgCdTe) near infrared camera attached to the 0.8m Cassegrain reflector at Fan Mountain Observatory, 15 miles south of Charlottesville, Virginia. It images an 8.5 x 8.5 arcmin field of view with 0.51 arcsec pixels through a variety of broad band and narrow band filters, including JHK_s, Brγ, and H_2. The polarizers are mounted in one of the two camera filter wheels in the cold collimated beam near the re-imaged pupil and are oriented such that the direction of the separation of the split polarized images from one prism is rotated 45° relative to that from the other prism. The linear Stokes parameters of uncrowded point sources over a 7.5 x 7.5 arcmin field of view may be measured by aperture photometry of pairs of images acquired through the two prisms. Initial obervations of polarized and unpolarized standard stars show that measurements of the degree of polarization are repeatable to within a few tenths of a percent, consistent with photon counting statistics. More standard star observations will be necessary to determine precisely the instrumental polarization and position angle offsets, but they appear to be stable and reasonably small.